Category: Uncategorized

It was the travel day of our two week vacation. Time was getting short before we had to leave to catch our flight. I put full propane tanks on our Defender and Patriot traps, replenished the Octenol attractant, and restarted each trap. I was relieved to see the Patriot start, as it was sometimes balky starting, especially with a newly filled tank in which there is sometimes trapped air requiring bleeding and perhaps several restarts. I was surprised that the Defender didn’t start, but less concerned, as this trap was modified to use a NodeMCU ESP8266 chip with WiFi supporting remote control, so it could be restarted from anywhere in the world having an internet connection.

This Defender was placed in a critical location between a wetland area and the pool. Its job is to intercept mosquitoes before they can attack pool goers. This season, it has caught enough mosquitoes to pack and overflow the catch basket three times. That’s a lot. The Patriot is behind a patio area to catch mosquitoes coming from other locations. The Patriot catches disappointingly few mosquitoes (a few hundred this season so far).

I tried to start the Defender twice before leaving, but was willing to sacrifice the evening’s catch in order to not miss the flight, given that we would have internet after we landed.

I tried to start the trap perhaps 8 times the next day, but the combustion chamber temperature reported by MQTT refused to go up by more than a few degrees Celsius, so each time the trap shut down in a fault condition. In the past, trapped air was generally purged after maybe 4 or 5 starts at the most. I started to wonder. Before I left, I had made sure the tank gas valve was open (after a couple of incidents during the past years). The on/off switch indicated on. There was a reported 3-5°C temperature rise during each start, indicating that at least the igniter wasn’t burned out, and that the fan had blown the hot igniter heat through the catalytic converter to the thermistor probe.

I tried running the igniter during the warm up phase, where it normally would be off. At one point, it ran for 600 seconds (10 minutes), to no improvement. Later attempts failed to yield much or any temperature rise. I had to give up and hope the Patriot would take up the slack.

Day 1

Back home after two weeks, the Defender still didn’t start. The power cord was intermittent, kept falling out. Closed and reopened the gas valve, restarted again, no effect. Later I started charging a spare sealed lead acid battery to run my tire pump for blowing out the nozzle. Could not find the clips to cigarette lighter adapter. Attached the tire pump with clip leads, set the tire pump to max (119) psi, run for a bit, and the leads begin to smoke. Scrounged some heavier duty wiring, tried again. The pressure eventually drops, but so does the compressor speed.

(The “modern” tire pumps use a digital display to set the desired pressure, then, when the pump is turned on from being off, display the pump pressure as it fills the tire. Better for this purpose is the previous generation that has a simple power switch and an analog gauge. The modern pump will not start unless the battery is connected with the switch off, and then the switch turned on, very inconvenient, especially for projects that require automatic pump operation, such as keeping an old, brittle, leaky top ring of an above ground pool inflated.)

I lifted off the case top cover (no screws) and took a look. It was disturbing to notice a dark spot on the controller PCB under the igniter MOSFET. Running a cycle, the igniter remained cold. Disconnecting and taking the Defender “power unit” inside, washing out a (3 overflowing baskets) season’s worth of dead mosquitoes and mosquito parts, and removing the controller PCB assembly, revealed PCB charring around the igniter MOSFET, and heat damage to the adjacent fan connector. The igniter Molex pin connectors were mottled with some yellowish corrosion-looking spots.

Measuring the igniter LR2703 MOSFET showed a defective source to gate junction. Removing the MOSFET caused the drain pad to detach from the charred circuit board (should have used the hot air station). Scraping the board to clean it removed most of the charred material, but the woven layer below was black in color, indicating a chemical change.

The use of the PCB as a heat-sink was in this case inadequate to handle 10 minutes of igniter operation on a hot day, especially given that the gate was driven by a 3.3 volt logic signal from the ESP8266, not 5 volts from the PIC controller. The LR2703 really needs that 5 volts to give a low on resistance, current limiting at 20 A. But at 3.3 volts, that figure is close to only 4 A, and the Rds is about 1.5 ohms instead of about 0.1 Ohms. When hot after 3 seconds, the installed 12 volt silicon nitride igniter resistance is 7.5 to 5.25 Ohms, and draws 1.6 to 2.3 Amps. (When cold, it is about 5 times that, but this is limited by the power supply transformer and line cord, and the MOSFET.)

No spares were on hand. Just as well, as this MOSFET type is unsuitable for 3.3 logic level drive, and the PCB was ruined for use as a heat sink. Searching for a better alternative yielded the TO220 IRLZ24N Power MOSFET, which was ordered (next day!) along with some high temperature silicone adhesive to attach the lifted pad and the TO220.

Day 2

The MOSFET(s) and adhesive arrived the next day, but too late for any work.

Day 3

Attaching the pad with the high temperature silicone adhesive was a complete mess, I wished I had used high temperature epoxy instead. However, the pad could not be used for contact to the TO220 anyway, so the adhesive was used to attach the TO220 on top of the PCB MOSFET location. Because TO220 leads are thick and stiff, the concern was that they would rip up the existing PCB source and gate pads. The leads were carefully attached with a short loop of fine stranded wire that could flex and not put excessive pressure on the pads. The drain was attached directly to the Molex connector pin. The adhesive gave the TO220 some additional flexibility so that temperature variations would not rip the source and gate pads off the circuit board.

The circuit failed bench testing. Examination of the wires connecting the NodeMCU to the original controller board revealed that the red ignition drive wire had come loose from the PCB. This was attached, tested, and the new MOSFET worked. Powering the igniter, the MOSFET got warm, but not too hot, so a heat-sink was not added.

The intake temperature and humidity sensor had not worked all season. There was no obvious sign of of damage or contamination. Fortunately there was a new sealed HTU21 module, to which a connector was added. The sensor was connected, and the trap displayed valid temperature and humidity. No idea why the old one failed, it is marked and saved for “future investigation.”

The battery and tire pump were brought inside, connected, and the pressure measured at 98 psi, a high value, but this inaccurate measurement is not comparable to previous measurements using an older style analog pump.

I disassembled the trap, cracked the case, and cleaned the nozzle first in mineral spirits, then in brake cleaner in a plastic cup in an ultrasonic cleaner for 30 minutes. Reassembling the nozzle, I saw something that looked like plastic in the ring around the nozzle. I don’t know how these work, but guessing that the propane comes out of that ring, picked the white material (from the plastic container?) from the ring. The nozzle was reinstalled in the combustion chamber. Having long ago decided that the existing adhesive seemed to be sufficient, no adhesive was removed or newly applied.

Connected an auto tire air compressor set to 119 psi, and blew air through the nozzle. Apparently the pump has been damaged as it displayed only 888 and not the nozzle air pressure – another project.

The three Richco PCB standoffs were in bad shape, so they were replaced. I had purchased a bag of 100, so why not? Not so fast! Remnants of the old standoffs were stuck in the case, requiring a drill to clean out. Regrettably, the drill apparently damaged a second thread (the first was damaged years earlier, some people never learn), and two of the clips aren’t tight when threaded into the case. But they don’t fall out!

Heat damage to the fan connector was cleaned up, but the fan failed to start. This new fan issue was treated by extracting, with great effort, pins 1 and 3 of the female Molex connector, then cleaning and re-bending them to make tighter contact. (Too bad pin 2 was not treated, as it is the active pin, not pin 3!) The fan worked better, but was not perfect. There was a not fully inserted position in which it worked, so it was left partially inserted, therefore intermittent, deferring a complete repair to “the future.”

The trap was reassembled, deployed, and started. Of course it didn’t work. But at least the trap was back to where it was before I smoked the LR2703 from afar.

Was the ignition somehow degraded? Applied DeOxit to the AC connector terminals. No effect. Rain started to fall. Inside I made a list of possible issues: 1) power supply “weak” (many players here), 2) nitride igniter defective, not hot enough (and no new spares!), 3) Nozzle still obstructing (but just cleaned!), and 4) No gas flow (but the gas valve clicks!).

Day 4

Swapped power supplies (transformer and low voltage line cord). No change.

In the past, there had been examples of igniters that get hot connected to a battery, but don’t work in the trap. The Mosquito Magnet spare parts bag includes 6 igniters: 1 original open circuit, 1 open circuit silicon nitride, and 4 silicon nitride igniters that somehow stopped working and were replaced by new ones. That’s a lot of partially failed igniters, especially given that these are supposedly more robust than the originals. Two new silicon nitride igniters were ordered from different sellers (as if that would matter). Delivery times were on the order of 2+ days.

In the meantime. The igniters were measured using a hand held infrared temperature probe designed for areas larger than the small tip of an igniter. Temperatures indicated from 323-392°C, way too low. Propane’s ignition temperature in air is 493–604ºC. Igniters run much hotter, 1180-1330°C. The igniters were connected to a 12V sealed lead acid battery, and they glowed hot enough (but not white hot) to ignite propane from a torch (but the flame went out as the torch was removed from the igniter, why is that?).

Other time was spent inventorying the other spare parts. There were lots of nozzles, including expensive 6 WDA (water use) nozzles, at one time mistakenly believed to be correct replacements for the trap.

I really wanted to run the trap to catch some mosquitoes. For this, manual lighting would be OK. I tried lighting the trap twice using a wooden kitchen match, but this is nearly impossible as the wind from the fan just blows the match out before it can be inserted into the combustion chamber.

Day 5

The first new igniter arrived, was tested with results similar to the others above. The igniter was deployed, and the trap didn’t start, just exhibiting the normal 3-4°C temperature rise. Bench tested the removed igniter. It performed nearly identically to the new one.

Was it the new MOSFET, the power supply, or the full-wave bridge rectifier? The igniter connector was disconnected and placed outside the case, an adapter wired, and the battery was used to power the igniter during a cycle. The trap still didn’t start.

It had to be the gas. The original regulator had failed a few years back, causing strange combustion behavior. The new regulator was the same as that now on my much newer Patriot, only even yet newer. Was it the nozzle?

Day 6

The spare parts did have a new nozzle, never used. The case was cracked, the nozzle installed, the trap assembled, and cycled but I forget to open the propane valve. After a while, I realized this and tried again. Still nothing. The trap didn’t start. Getting tired of this.

 

Was it the tank or the regulator? I remembered there was no “pop” when removing the regulator from the tank like when removing a full tank from a trap. Switching tanks with the working Patriot, the trap was cycled, but didn’t start.

Day 7

Was there any gas flow? Finding the remains of the hand made pressure test fixture that screwed into the Schrader valve, the BMP180 pressure sensor having been fried by mis-wiring on another project and removed, leaving an open slit in the plastic bottle. The fixture was screwed into the Schrader valve, allowing any propane to escape, and the trap started. There was no hint of propane from the bottle, and a spark failed to detect any propane. No gas flow!

What about the “gas reset tool?” This was located and tried, but did not fit either Defender or Patriot regulators, which have a much smaller center hole for some purpose.

This leaves the regulator and valve. I had another regulator from the regulator bake off a few years ago, and a spare valve assembly used for nozzle pressure testing. Taking the spare apart revealed that it was missing the internal plunger and spring. If the valve were defective, the plunger could be bypassed by opening the valve and covering the stopper part with wide package sealing tape. The regulator output pressure of 11 inches water column is quite low, so the tape could temporarily contain the gas. This obviously unsafe practice is not recommended.

While contemplating unscrewing the regulator, a weary snap decision was made to bypass the valve instead. A T10 screwdriver removed the actuator, the parts not lost in the yard (amazing!), and ordinary clear sealing tape (unrated for sealing propane valves, so not recommended) applied. The trap was started, and in due time the satisfying ignition pop was heard. Success!

But then smoke started pouring out of the exhaust port. What was this? Not really concerned about fire in the combustion chamber, I wondered as to its cause. Was the trap started so many times that something built up inside like a car that doesn’t start then backfires? How could that be given that there had been no gas flow? Was some contaminant added to the combustion chamber? Some unlucky insect (but no organic burning odor)? Loose adhesive sealant? What? It took several minutes for the smoke to stop.

The smoke stopped, but then the combustion chamber temperature kept rising. Normally, this Defender runs at about a 92°C temperature rise above ambient. At 23°C, that would be 115°, maybe 120°. The NodeMCU high temperature cutoff had been set to 140°C, and the trap was getting close to that. The command to set the limit to 150°C came too late, and the machine entered an over-temperature state, the software shutting off the gas until cooled, then fan off, and fault indication. But the valve was bypassed, so the gas stayed on! Manually closing the tank gas valve started the cooling. It took a surprisingly long time to get to a reasonable temperature. The high temperature cutoff was set to 160°C, the gas valve opened, and the trap restarted, and the temperature again took off.

After 3 hours operation the trap was still at 146°C (see MQTT Legend below):

Temp=145.9C (0) at 5:13655 F=1 I=0 G=1 S=1 E=0 T=23.4C H=50.4% M=26584 (142/1024:3031) R=70~160 W=-81.85 B=0.0 V=3.5

I have no explanation for this hot running mode. It remains to be seen if this trap catches any mosquitoes.

Day 8

Check the Defender, running:

Temp=148.3C (0) at 5:66690 F=1 I=0 G=1 S=1 E=0 T=27.1C H=48.5% M=26568 (135/1024:2858) R=70~160 W=-82.85 B=0.0 V=3.5

Shut down to remove the tape and install the valve actuator without losing the actuator or damaging the very thin O ring. Start the trap. Fan does not operate. Notice that the power connection is intermittent, then no fan even with power. Multiple system failures. Remove the power head and take it to the lab.

Printed the schematic and troubleshot the 12V supply and connections, hard to do with conformal coating preventing probing. Soldered foil side pads to burn through the acrylic to get a test connection, 12V measured 12V. But still no fan, although the NodeMCU drive pin was high. Removed the PCB from combustion chamber, and discovered that the blue fan wire was disconnected from the PCB via that connects the original PIC controller to the Fan MOSFET, the second broken wire this round. Unplugged all connectors, and reconnected the wire. Then, in a fit of pique, used acrylic glue to attach that wire plus the red ignition lead to the PCB for strain relief. (Click the 2019 before picture twice for a closeup, and to get an idea of the workmanship described here.) The other wires connect to pads or terminals that should withstand some wire movement. The acrylic puddle would take some time to set.

Waiting for the acrylic to set, examined the now completely non-functional attachment points for the AC connector. Decided to rebuild these!

The quick way is to cast new plastic, but all the casting materials had long ago expired, and where were they, anyway? Found some epoxy putty in the basement with no expiration date. Cutting a chunk and mixing it was rather difficult. The material was quite stiff and not sticky. Applied it but then immediately removed it and cleaned up. Considered Shoe Goo, a marvelous material, but decided it would not be rigid enough. This left JB Weld, which takes a day to cure, and several hours to set enough to maintain a shape. Without materials to make a mold or fence to contain a viscous liquid, I mixed the material anyway, here goes!

Initially applied the epoxy to the three chamber mounting posts, which had stripped many tear-downs ago. Applied the rest to the AC connector posts. Working this material took hours. After about 3 hours, it was the consistency of a thick putty, perhaps too thick. I kept working it into a solid around the original posts. Several incidents of dripped epoxy on clothes, the rug, etc., necessitated emergency measures involving alcohol and soap, while the material continued to flow. The most ruined post just would not be reformed until a small twist drill was positioned and the material stuck to that. This formed the basis of a structure to which the flowing material could be attracted. There was clay that may even still be good around somewhere that could have been used to create a form to contain the epoxy, but the clay, although vividly remembered, has not actually been seen in a few years. Anyway, after a few punishing hours, posts were formed, and the whole thing left overnight to cure.

Day 9

Checked the JB Weld, looks solid. Drilled pilot holes, and larger holes in the new posts. Cut threads with screws. Use an end mill to clean up splatter from case, but this made a mess. Used a wire brush to clean that up. Vacuumed and blew out chips and residue. Checked the main chamber support posts. Try a screw in the post by the gas line, hear a crack as it breaks from a horizontal piece, not essential. Drill pilot and tapping holes in this and other posts. Vacuumed and blew out the case bottom. Mounted the combustion chamber assembly using 3 screws, which are solid in the posts for the first time in years. The #2 Philips screwdriver has some difficulty turning the screws. They are all tightened to flush, but not more.

Oops: what about the PCB foil coating exposed for testing? Sprayed acrylic coating for artwork on the PCB circuit side. Dries in 15 minutes. Let sit for an hour.

Mount the dried controller PCB in trap. Oops: forgot to wash some acid flux from the PCB before spraying the acrylic. Oh, well. Scrape the AC connector male contacts with file to remove oxide. Screw the AC connector into the new posts. Solid. A big success.

Test run no gas. MQTT temperature reads -43.7°C or so, a symptom of no thermistor connection. Remove the acrylic from the thermistor male connector, remove the contacts from the female connector to clean, difficult. These are gold plated contacts. Measure the thermistor at 100 kOhms, Ok.

Bring a nearly but not completely empty propane tank to the lab, connect it, and start a run. 10-15°C temperature rise. The valve works. Deploy to the outside location, connected, and started, The trap is working.

The ambient temperature sensor is currently incorrectly positioned above the intake air flow, where it is much hotter from the combustion. This will be adjusted after a day or two of catching mosquitoes.

Day 11

The dreaded offline MQTT message shows up. Go to the Defender, the power connection is intermittent in the sunlight and hot day. Wrap the power cord around the gas line to press the connector into contact. Go to the office and order a contact burnishing tool (plus some quick setting epoxy putty!). Positioned the ambient temperature and humidity sensor to be more in the air intake. Very few if any mosquitos caught so far, perhaps the air temperature is still too hot.

Temp=150.8C (0) at 5:7920 F=1 I=0 G=1 S=1 E=0 T=34.1C H=48.5% M=26680 (128/1024:2689) R=70~160 W=-78.85 B=0.0 V=3.5

Discussion

The pressure to repair the Defender quickly is a major impediment to quality work. A lot of this effort is the “chickens coming home to roost” result of shortcuts taken in the past, plus countless dis- and re-assembly cycles.

How odd it was the gas valve. It was the next to last thing to check. How lucky to have tested this before replacing the regulator, which would have a chore. Clicking when turned on, it seemed to be working. Disassembled, there was no apparent damage or fouling. However, the trap now runs hotter, so maybe something was dislodged during disassembly.

Currently the Defender combustion temperature is running at indicated 150°C, which was the temperature with the propane valve wide open (just sealing tape where the actuator is). This is substantially hotter than in the past, where it has run at about 90-100°C above ambient. This temperature rise means that there is more fuel or a more favorable mixture present. Previously the trap had collected three completely full catch baskets of mosquitoes prior to failure, so I do not believe the previous mixture (fan output) was too low, as unburned propane or carbon monoxide repels mosquitoes (or so they say). This implies that there is more fuel flow either from more fuel pressure from the regulator, or the new nozzle is allowing more flow, or there was some now removed obstruction in the valve.

The 150°C combustion temperature may not be a bad thing, other than for propane consumption, as long as it catches mosquitoes. Unfortunately, the weather has turned cool and dry here, so fewer insects are expected. We will just have to wait and see.

If the catch is poor, then it may be because of a too-high combustion temperature. Troubleshooting the nozzle will require repairing the analog tire pump, which suffers from a worn-out seal, and lasts for only a few minutes, and reviving the pressure sensor, which, will require some reprogramming and liquid plastic (or Shoe Goo) to seal the sensor inside of a bottle.

I do not believe I can just let the higher temperature issue go, given that the Defender has caught more (three packed-full baskets) mosquitoes this year than it has ever done in the past, and so many orders of magnitude times more than the newer Patriot.

Stay tuned for updates.

Defender MQTT Legend

Temp=145.9C (0) The combustion temperature measured by a thermistor connected to a rod placed in the exhaust just after the catalytic converter, and the change since the last reading.
at 5:13655 State (5 is running), and seconds in that state.
F=1 I=0 G=1 S=1 E=0 Fan on, Igniter off, Gas on, Switch on, Error none
T=23.4C Air intake temperature, a bit warmer than ambient
H=50.4% Relative humidity
M=26584 Number of bytes of free memory
(142/1024:3031) thermistor voltage, reference, calculated resistance determines combustion temperature
R=70~160 Under and over temperatures to cause a fault.
W=-81.85 WiFi signal strength, last digits of the internal IP address
B=0.0 Web server status (idle)
V=3.5 Defender NodeMCU software version.

You can access the Defender (currently MMD/esp8356707) using an MQTT client  on broker.hivemq.com. Subscribe to MMD/# to get this and other devices.

 

For the first time in several years, I was standing in my driveway a few days ago during the day, and found myself attacked by a mosquito. Other family members had been reporting mosquito bites, but it seemed too early in the season for that, so I ignored them. However, after 2-3 more attacks plus two bites, that was enough. Time to fire up the traps!

My 16 year old daughter has taken an interest in machines, including small engines and legacy computers, so I invited her to help me set up my un-trusty circa 2002 Defender, modified a couple of years ago with the substitution of a ESP32 WiFi module to replace the Defender’s PIC controller, which I had stupidly blown up troubleshooting the trap’s many problems. The modification was done in a slipshod manner, and has not and was not expected to withstand the elements for prolonged periods of time. Compared with my newer unmodified Patriot, this unit is far more interesting and complicated, more can go wrong, so it was first, with the other on deck.

She plugged it in, and the fan started to spin. I opened my MQTT snooper app, and there was the Defender reporting its status. Nothing wrong with the electronics! I asked her to then attach the propane tank, and turn on the gas.

After a few minutes, the temperature rise was only 4°C or so. I waited for a while for the trap to enter the error state and turn off the gas, and restarted. I remembered that a new tank of propane in which the air is not bled after filling can take several attempts until the air finally bleeds out into the trap, and the propane is sufficiently pure to sustain combustion.

Well, I tried that 4 times, with the same result: only a very modest temperature rise. I then decided to try to bleed the tank like I saw my local hardware store (which charges a fortune for a tank refill), so I went to the tank. The bleed valve looked like it took a standard slot screwdriver, nothing fancy. However, finding a slot screwdriver took some time; it seems they are very popular with the tool “borrowing” crowd. Finally, I returned to the tank, inserted the screwdriver, and turned it to release the air.

Nothing! Nothing came out, not air, not propane. What? I used the screwdriver on an adjacent tank, which spitted air and propane, just like at the store. What could be wrong? I decided to substitute the propane tank. Picking up the Defender’s tank, I suddenly realized that it was empty! My (now long deserted) daughter followed my directions and connected the tank without mentioning that it was very light. I wanted her to do all the steps, so I never touched the tank. I thought that I had filled all the tanks at the end of last season, and could not imagine that there was an empty tank in line to be used. Moral of the story and new rule of thumb: you cannot start a trap with an empty tank.

This now highlights the need for an additional sensor to weigh the propane tank and hose so that a trap can have a new tank before it goes stop (with quick replacement action, the trap can keep going without restarting). Such a sensor would have alerted me immediately to the empty tank. Or I should follow my standard practice of weighing every tank before putting it on a trap. But the mosquitos were biting. I am ashamed to say I still haven’t weighed the tanks… Fear? Laziness? Both?

I had made some weighing scale design progress, but have not solved the issue of weatherproofing the strain gauge sensors on which the tank would sit. Any recommendations (via the forum) would be appreciated. How can we reliably weigh the tank in real time?

A few days ago, while acquiring data, I inadvertently interrupted the AC power to the old Defender, resetting the trap. Power interruptions happen all the time here, but this one somehow changed something, I don’t know what, and the normal operating temperature rise from the intake to the exhaust increased dramatically from ~85°C to ~94°C. Surprised, I tried cooling the trap to near ambient and restarting, but the thermistor temperature rose and stayed high, in the 130° range, close to the 140° limit I had set.

Puzzled, I reviewed my notes and blog entries, and discovered that this was a very typical range 2 years ago. I might have been using the wrong nozzle at that time. Since the change, during the last two days, the trap had caught only 20 mosquitos (although I didn’t see any around), compared with several hundred in the previous day (although just after a rain). The trap was running at about 128° with an ambient of ~34°, for a 94°C rise.

I then tried the electric tire pump on the Schrader valve, and it read 105 psi, which is very high. I ran the pump for several minutes, but there was no change in pressure – nothing was dislodged. Restarting the trap, the temperature rose even higher to almost 135°C. I had made it worse. It may not be a good idea to use an flaky auto tire pump to clear out a hot trap. Perhaps the contaminants from the worn-out oil-free pump have really clogged the nozzle, although the pressure went up high and stayed there. In any event, the nozzle had to be cleaned or replaced.

I found an old nozzle that had been cleaned and had a like-new 40 psi test fixture result. I was determined to change the nozzle as quickly as possible, no frills. Fortunately, I have a high torque electric screwdriver, so with that plus 2 large slot screwdrivers to open the combustion chamber, and nothing else, away I went.

Fortunately, the awful top case screws are long gone to a better place. Power off, remove the basket and top cover, unzip the 3 sheet metal screws into stripped plastic supports, unscrew somewhat the two hose clamp screws, remove the power jack, remove the solenoid from the valve, and it all lifts out. Turning the assembly on its side, remove the 3 machine screws holding the plastic exhaust port from the combustion chamber, then the last 5 screws holding the chamber together. Taking care to not break the circuit board, NodeMCU and other stuff, I used the two large slot screwdrivers to pry the case apart, and it popped open without too much effort. (I had a few times back in the past given up on applying new gasket sealer to the case, the old stuff seemed to work just fine, and nothing looked like it was leaking out, so there.) The nozzle assembly came out with some rotation, and then I replaced the nozzle. Reassembly occurred, but not before using the hose to spray the awful remains the last couple of year’s catches.

A bit of DeOxit on the power connector to try to address the intermittency, and, amazingly, the trap started without issue. The connector is still intermittent, however, but this was not the time to fix that. The mosquitos scored 2 bites, maybe real, perhaps imaginary bites. Not bad.

The trap with the cleaned nozzle went up to 127°, a 96° from 31°C rise, but has since calmed down to 124.6 – 33.1 = a 91.5°C rise. I don’t know whether this is a better operating point or not, only the catch rate can tell this, but at least a clogged nozzle has been changed. I have been measuring tank weights and catches for 3 days now, another post will provide some results.

After getting the Defender up and running then failing on Thursday, restarting, and failing again Friday morning, after repositioning the NodeMCU and restarting, by mid-day it had caught about 10 or so mosquitos, not too bad. These mosquitos convinced me it was time to start the Patriot, and perhaps get cracking on the Liberty conversion.

At the end of last season, the Patriot was suffering some failures during a run. Normally, a failing trap fails to start, but stopping in mid-tank was rare. I tested the pressure last year with the auto tire pump, and it was high. I decided to test again and clean it if necessary before deployment.

My test pump, a Viair P70 purchased in 2015, had suffered after being used to keep a ring-type above ground pool ring inflated. After two seasons, the ring had become brittle, and had several large tears, and several small leaks, which I had patched, and was able to inflate, with a slow leak. This required the shop vac to be applied every day, and after a few times when the plastic bag covering to the vacuum blew aside and let the rain in, the vacuum bearings started making a screaming noise, adding to the experience. When I was not perfectly diligent, a few times during the cool of the night, the ring deflated to the point where a cascade of about 1000 gallons of water escaped over a partial collapse on the pool’s low side. I dreaded waking to see this out the window or on the pool cam in the morning.

So I took the Defender software and adapted it to a pool ring inflater. This required a 12 volt battery, pump, trickle charger, 5 volt auto adapter, a solid state relay, and a pressure sensor, plus additional temperature and humidity sensors connected to a NodeMCU on an interconnect breadboard. The pressure sensor had to measure very low relative pressures absolutely. I made on using two paint mixing sticks and a 100 g strain gauge. The ends of the sticks were taped to the ring about 30″ apart, and the ring pushing against the strain gauge deflected it enough to measure. The previous and now backup visual measure was provided by leaning the pool skimmer handle at about 45° against the ring. If it sank less that 1/4 handle width, the ring was ok. Full scale was about 2-3 rings sunk into the ring. Water would flow soon after.

The system worked beautifully. However, as time passed, additional leaks developed, one or two every few days. Unless these were identified and repaired, the system would be pumping so much that the energy removed from the battery could not be replenished by the trickle charger in time for the next inflation, and the system would enter a downward spiral eventually ending in failure and excessive battery discharge, and the lost 1000 gallons.

The first pump, $10 from Harbor Freight, was quite small, and took several minutes to reinflate the pool ring. This wore out right away, and I had “repaired” the pump once or twice before (the pump piston seal if overheated looses its flexibility and does not seal effectively). So I use my “good” pump, the Viair P70, and it was very effective, until it too started failing, with the same issue. After a few repairs, trying various things like silicone grease to improve the seal, which was a disaster, the pump would last only a few days before not pushing any more air, or worse, leaking air from the pool ring. I tried to purchase a new piston seal, but was informed by the Viair rep that the pump was obsolete, no parts were in stock, and I would be better off buying a new pump. This was very disturbing news, as I hate planned obsolescence.

Back to the Patriot. I had ordered two pumps with analog meters and no digital on/off to replace the Viair. That in itself was a problem, since the replacement pump for the automobile has a digital set point, and requires toggling the on/off switch to activate the pump, which prevents turning the pump on by applying power (as in the inflater), and also prevents its use to measure the Mosquito Magnet valve orifice conductivity as inversely proportional to the pressure with a given pump output.

Anyway, the working-for-now Viair pump showed 102 psi, pump A, 89-86 psi, and pump B 83 psi. This was much higher than the Defender good nozzle pressures in the mid 30s, so the trap had to come apart. This was easy because the case screws were removed last year when the trap started failing. The Patriot nozzle is held in by a single Philips bolt, although three screws must be removed to raise the assemble above the case bottom to remove the nozzle.

The nozzle had no markings, and the orifice consisted of a single hole in the center of the head. This hole is about 0.010″ in diameter, or about a #87 drill bit size. I don’t have this size, but a #30 wire wrap wire fits perfectly. I could see some black material in the orifice, and holding the nozzle up to the light, it looked blocked, so I tried to use the wire wrap wire to dig it out. This caused the wire to break and lodge in the hole. A variety of stiff, sharp objects later, the blockage was gone, and the hole clean looking. Hooking it up to the pump showed pressures on 80 psi for the Viair, and 60 psi for pump A (pump B was disqualified for its clunky digital pressure gauge). This is still higher than a Defender, but the hole blew air perfectly, and I reassembled, and started the trap. The trap worked! I put in an octenol cartridge and left it running.

When checked today, both traps are running and catching mosquitos, even though we have not noticed mosquitos in the evenings. The mosquitos in the Patriot seem particularly agitated, angry even, don’t let one escape! No explanation for this other than perhaps the more spacious Patriot basket with its clear top prompts the mosquitos to fly up into the hard plastic.

So begins the 2021 mosquito season.

What a miracle. I replaced last year’s NodeMCU software with a latest and greatest tech version now released on the wiki, patched accordingly, started it up, and it is running. You can see it working (or not), using an MQTT client connected to broker.hivemq.com. Follow the MMD/esp8356707 topic, or MMD/# topic wildcard to follow any and all other units in development. Here was the one of the initial messages:

Temp=120.8C (0) at 5:465 F=1 I=0 G=1 S=1 E=0 T=34.5C H=17.6% M=26920 (243/1024:5857) R=70~140 W=-73.85 B=0.0 V=3.5

(Kindly refrain from sending commands to the Defender, thank you. We are testing the new board and software.)

I should mention that we are suffering from wireless connectivity issues caused by the proliferation of poorly designed wifi-6 and mesh routers and access points, however, the NodeMCU recovers fairly quickly, so a short duration MQTT “offline” message every now and then is to be expected until the router manufacturers update their products to not interfere with low band IOT devices.

We will see how long this lasts. It is amazing to me when things like this “just work.” As I was writing this as a reply on the forum, I was forced to type:

“… Well, I spoke too soon. While typing this post, the system went off line, and restarted.

Temp=124.8C (0) at 5:779 F=1 I=0 G=1 S=1 E=0 T=34.7C H=18.9% M=26920 (223/1024:5241) R=70~140 W=-72.85 B=0.0 V=3.5
Offline
Offline
Temp=118.6C (-0.2) at 1:3 F=1 I=0 G=0 S=1 E=0 T=34.9C H=19.6% M=27440 (255/1024:6242) R=70~140 W=-74.85 B=0.0 V=3.5…boot

The unit is going offline periodically for periods of ~22 and ~45 seconds. It is rebooting.”

That was the end of that post. I copied the text, canceled the post, and continued investigating.

The system would not stay running, repeatedly rebooting. Worried about the igniter failing because of too many cycles, I sent it the MQTT command to cool down with error. The error transitions the trap into an error state after the cool down. The idea was to see if a cool trap had issues with connectivity and rebooting. The previous hardware was able to function to 35°C without issue, and this was close to that. However, the ambient intake temperature is not the same as the temperature experienced by the NodeMCU, which is adjacent to the combustion chamber, nearly touching it.

After several hours, the intake (and combustion) temperature dropped to 17°C, quite a bit cooler, and I restarted the trap. It ran all night, but failed at 9AM, with last words:

Temp=124.8C (0) at 5:39647 F=1 I=0 G=1 S=1 E=0 T=38.7C H=21% M=26800 (223/1024:5241) R=70~140 W=-74.85 B=0.0 V=3.5

The ambient temperature of 38.7°C is pretty hot. This suggests that the NodeMCU was getting too hot for reliable operation. Downstairs, case off (Not difficult: I removed the screws several seasons ago and put them in a safe place, or did I?). The new NodeMCU was fairly deep inside the case, nearly touching the combustion chamber. I was thinking of inserting a fiberglass cloth, or some sort of heat shield, when I noticed the rather stiff wires to the “power” switch. “Maybe I could use these stiff wires to push the NodeMCU away from the combustion chamber” I thought. So I re-routed the wires to do exactly that. What a proud boy I was. Not only was the board further away from the chamber, there was no restriction to any air flow (what?) from a heat shield, not to mention being a low cost solution, although it does require “tuning” in the form of wire bending. It has been several minutes now, and it is still working:

Temp=120.8C (0) at 5:2476 F=1 I=0 G=1 S=1 E=0 T=29.1C H=36.3% M=26688 (243/1024:5857) R=70~140 W=-73.85 B=0.0 V=3.5

2476 seconds and still running! However, it does seem odd that the ambient temperature sensor is reading much lower than before. This Add-On is lacking certain mechanical sophistication. Perhaps the wire bends positioning the ambient temperature/humidity sensor may be a bit too imprecise.

Another issue is that the switched voltage divider scheme is giving a too-high value of 1024 for the open circuit state. The other hardware (boards) have had the open value of 1015 or so. The circuit (see the wiki) switches the ThermLo net between ground and open circuit. When grounded, the analog-digital converter (ADC), measures the voltage from +5C (connected to 3.3 volts from the NodeMCU regulator) into the divider with R5 (20k0) on the top, and the thermistor on the bottom into the ADC input (a ~330 kOhm divider). When ThermLo is open, it measures just R5 to the 330 kOhm input. This scheme allows the software to calculate the thermistor resistance by a ratio, and not depend on the imprecise 3.3 volt regulator as a voltage reference. However, the open circuit measurement must not exceed the full scale value of 1023 (or 1024), doing so will lose precision. Evidently the NodeMCU +3.3 is a bit too high, or the resistors into the ADC inaccurate, or both. Another issue to investigate.

Still, even without the added precision, the combustion chamber temperature probe does its job. Maybe I can forget about switching the bottom, and just rely on the kindness of the circuitry as it is and use the values as they are, and it will work sufficiently. This would free up a pin to use for something else, some other feature, for example, an additional indicator light for the Liberty, or some such.

Well, while I was writing this, the unit went off line again, last words:

Temp=121C (0) at 5:2674 F=1 I=0 G=1 S=1 E=0 T=29.5C H=39% M=26688 (242/1024:5825) R=70~140 W=-72.85 B=0.0 V=3.5

That was just after its triumphant report a few paragraphs above! Gotta go, see what happened, see you later!

… (Passage of time)

Back again. Mechanical iffy-ness includes the draping of the power cord from the house to the Defender across a walkway, with a loose coil at both ends. This is insufficient to handle a hose pulling the cord forcibly away from the Defender. Fortunately, the 2002 design used a connector that will release with excessive cord pull without too much damage. The new Patriot, with its screw-on connector, will be less forgiving. Anyway, the unit is back on the air, and happy times are here again, again, at least for right now:

Temp=120.3C (0) at 5:735 F=1 I=0 G=1 S=1 E=0 T=30.2C H=28.2% M=26856 (246/1024:5952) R=70~140 W=-74.85 B=0.0 V=3.5

Welcome back to the Mosquito Magnet blog after a long off season. The forum has started to stir, a user has prodded me into releasing the source code to the NodeMCU software as a complete package, another user introduced me to a smaller but just-as-capable NodeMCU, the WeMos D1 Mini, and in preparing a release, updating the system software, etc., I needed a test machine, so I am finally starting the Liberty Add-On project. Check the wiki and forum, and stay tuned for more details.

On the forum, a discussion started regarding CO2 cartridges, and my reply started to veer off into blog land, hence this entry.

CO2 Cartridges

I think we have established that a clean nozzle is vital to the trap’s reliable operation, and that the CO2 cartridges are woefully inadequate (although I haven’t tried using one after each tank change!) to clear a clogged system. The problem is that the trap may fail to start because of some other issue, and using 3-4 of these irritatingly sort-of expensive and short lived capsules would drive anyone batty. Plus, the original directions of backing off and letting the CO2 flow for ?several seconds? when in fact it comes out in one quick “whoosh” adds an unacceptable dimension of doubt to the whole enterprise.

I should mention a few more details about cleaning here. I use brake cleaner, and haven’t tried MAF (perhaps more effective). After removing the filter, place both into a 4 oz glass jar, cover with solvent, and place the covered jar into a small ultrasonic cleaner filled with warm water, and run for about 30-45 minutes. This seems to work.

I then test the nozzle(s). I was fortunate enough to acquire a used Mosquito Magnet valve from ebay. I block the propane line intake port, screw the nozzle into the valve, and connect a prior generation electric automobile tire pump with gauge to the Schrader valve input. With the pump on, the cleaned nozzle reads 35-45 psi vs the >60 psi from an obstructed nozzle. If the nozzle reads high, it gets another round of cleaning.

Prior to starting the trap, the tire pump connected to a trap also gives the same indication of the nozzle’s condition. I have experienced pressures up to ~110 psi this way. My criteria for cleaning is trap failure, but this policy results in failed traps at inopportune times. For example, my “newish” Patriot trap was having trouble staying lit at the end of last season, but will I clean it before trying to put it in service? Nah. “Millions for Defense, Not One Cent for Tribute ‘No, no, not a sixpence, sir!'”

Actually, thinking about it, I probably should test the trap first, it’s just that I have to repair my prior generation electric tire pump(s) that have failed from overuse first. We shall see.

The Patriot survived the day and night on the patio, and was running this afternoon. i decided to deploy it to its operating location away from the patio. However, I didn’t dare to shut it down and restart it, only to find it not starting. So I moved it while running, set it down, and it has been running since.

They tell you to turn the machine off and let it cool before moving it. But this is undesirable for many reasons, chief of which is that the igniters have to cycle as the trap is restarted. These devices are just horribly unreliable, and now I have no spares. I had just replaced the igniter, and I didn’t want to cycle it, and I didn’t want to have to come back, possibly repeatedly, to make sure the trap was running. Plus, I had become adept at moving a running trap over the years.

The disadvantage is that the trap restart has not been tested. There is something wrong with this trap. It is only marginally working. The consequence is that I don’t know when the trap will fail again. Tomorrow? Next week? Next month? The next time it fails, it will be time to figure out why the tire pump pressure reading is so high, and why this uses less gas than the Defender and catches fewer mosquitos. Could the combustion chamber really be so clogged? It will be time to open it up and take a look.

In June, 2018, I was facing a new mosquito season with an old 2002 Mosquito Magnet Defender and a worse-looking Liberty. I needed a reliable trap to intercept the mosquitos on their way from the adjacent wetland to the house and yard, so I purchased a new Mosquito Magnet Liberty. Certainly, in the years since 2002, the company through its transitions and maturation, had been able to make their traps more reliable by fixing the problems that have been so often mentioned on these pages and elsewhere. I hooked it up, turned it on, and it “just worked.” Until the end of July, where it stopped with a flashing light, a fault. Tried restarting it, again a fault.

I hooked up the tire pump compressor to the Schrader valve, and the pump pressure gauge went to 140+ psi. This was way high. I let it run for a minute or so, but the pressure never fell, this must be a clogged nozzle. The Patriot disassembly videos showed that the Patriot was just an updated Defender, with a few improvements, and who knows how many cost saving measures incorporated. Anyway, one improvement is that the Patriot nozzle just fits into the metal case and is fixed with a single screw. There is no need to open the case to remove the nozzle, a great improvement!

The nozzle was also different. Instead of having a cone pattern, it has one single orifice right in the middle measuring about 0.31mm or about 12 mils. It has the removable sintered fuel filter that unscrews. I soaked them in mineral spirits for 1/2 hour, then into a carburetor cleaner (acetone and toluene) placed into the ultrasonic cleaner for 1.5 hours. The orifice was basically clean before and after, the fuel filter brightened up quite a bit, and passed air quite easily. I tested the nozzle using my test fittings and the tire pump, and the pressure read about 35-40 psi, which is very good (low). I also hooked up the tire pump to the Schrader valve again, and again, it read about 140 psi. Was the Schrader valve somehow blocked?

I re-assembled the Patriot after cleaning out all the awful detritus that had accumulated over two years. It started right away, and ran for almost a day before failing. I then replaced the propane tank, although it weighed ~20 lbs with a fresh one ~35 lbs. I remembered that this trap has been running for much longer than the Defender, which lasts 21 days, but perhaps the almost empty tank was causing problems. The Patriot ran again for two days. It had caught just 3 mosquitos.

This afternoon in the heat of the day (fewer mosquitos), I moved the trap to the patio and opened it up. I removed the thermistor assembly and the igniter. Amazingly, the nylon or plastic screw that holds the thermistor did not break, although it was severely darkened. What an improvement! The thermistor metal probe had some deposits that might cause a slight amount of thermal insulation, not good for a probe. I used a steel brush to clean that off, and measured the resistance while heating it with a hot air soldering station. It seemed ok, or at least it wasn’t broken. I watched the igniter during a start cycle, it turned red a bit, but not as much as I would have liked. The voltage across the igniter was 9.02 volts measured with a Fluke DVM, which is typical. I replaced the igniter with the last of my new ones, which lit up a bit hotter looking, although the new igniter was not suffering the deposits of the old one. Time to order more igniters, although these gadgets are not nearly as reliable as they are cracked up to be. This would be the second igniter that was not open but suffered from “not hot enough,” and this one came from the original trap.

Suspecting the regulator or valve, I removed the solenoid during startup and heard the clicking sound of the valve closing – the solenoid was working. Being too hot and lazy to remove the nozzle and check the flame there, I took the valve apart to expose the intake and exit. Opening the tank valve, I heard gas escaping. I lit the gas with a match, and there was plenty of flame, more than out of the Defender valve. The Patriot valve must constrict the flow additionally to reduce the gas flow, but it seems that trap delivers propane to the nozzle, I hope.

I started the trap, the thermistor assembly bracket got fairly hot to the touch, indicating combustion, but the trap went into an error code anyway. The case was not hot at that time, which is amazing to me. This makes me think the combustion and resulting temperature rise is marginal, or there is an under-value measurement issue like in the Defender. Evidently, there is a marginal condition there.

The trap has been running for an hour on the patio. Don’t sit outside near the trap! If it lasts the night, I will put it back where it protects the patio. Otherwise, I will have to investigate the “marginality” issues. Why is the temperature sometimes too low? Is it really too low, or is it a problem on the controller (like in the Defender)? Could it be too low because of an constriction in the combustion path, which would also cause high pressures with the tire pump test? I wish I had measured the trap when new for a base line. I can’t imagine that deposits would so completely clog the exhaust path to prevent free exhaust flow, but I have never been able to imagine the things that go wrong with these machines until discovered by myself or others. Stay tuned.

Another 3 weeks, another tank. It ran out yesterday, but I was too busy to replace the tank, so the mosquitos got a reprieve. Plus, I was amazed that moving my other Patriot to just outside the back patio seemed to be effective at making the patio usable for outside dining. My eldest, 16, was on the patio last week and complained of multiple mosquito bites around the ankles. Additionally, the above-ground pool was hard to use at night because of mosquito attacks. The Defender is between the pool and the (downhill) wetland. The Patriot was between the Defender and the wetland, but I moved it to outside the patio to address these problems. After moving the Patriot, the patio was mosquito free for dining. The patio dining success lulled me into slacking off the propane patrol.

Today we got over 1/2 inch of rain, but the rain has stopped, and that means joy for mosquitos. I finally decided to replace the tank, but the trap didn’t start! I forgot to turn the tank valve on. Silly mistake. I turned it on, and it still didn’t start. What now, another igniter problem?

No, the explanation is easier than that. When I was paying $20 (too much) to refill the tank, the operator used a screwdriver to turn a screw on the tank to “let out air.” She said this was necessary, especially for those mosquito trap users that run the tank down to zero. She was right. The no-nonsense Tractor Supply people will have none of this. Turn the screw yourself. I dare not. But the result is that the initial flow of gas is mostly air, and not propane. The trap will not start the first time within the starting time limit. This requires multiple starts until the air is bled out of the tank.

That’s all there is to it. If at first you don’t succeed, try, try again. That was easy.