Heatermeter v4.3 Temperature Reading without Probes


 
H

HansvanHorne

New member
Hi All,

I just finished assembling the heatermeter kit and seems like I am running into a problem.
Without any of the probes connected, I have temperature readouts on all four channels.

Pit probe: 287
Food1: 258
Food2: 266
Food3: 304

They fluctuate as well.

What I understood is that with no probe connected it should read "no pit probe connected"..

Anyone have an idea what could be wrong?
 
Did you go into the HM Config and select the proper probe type for each probe? That should be your first stop.
The next thing you should do is make sure there isn't a bunch of solder flux left on the board around the probe jacks and the resistors that are standing up and the caps over there. If there's a lotta flux there clean the area with a soft brush and some isopropyl alcohol (and let dry completely before you power up). Also, make sure you have good soldering on the above mentioned components.
 
Last edited:
RalphTrimble said:
Did you go into the HM Config and select the proper probe type for each probe? That should be your first stop.
The next thing you should do is make sure there isn't a bunch of solder flux left on the board around the probe jacks and the resistors that are standing up and the caps over there. If there's a lotta flux there clean the area with a soft brush and some isopropyl alcohol (and let dry completely before you power up). Also, make sure you have good soldering on the above mentioned components.
Click to expand...
Hi, sorry for the late reply (bit of an understatement haha), but due to the birth of my 2 sons (twins) and Corona this hobby was unfortunately paused for some time. Now I am back at it :) Thanks for the reply, and I did some research using the forum already.

I did the following (observations):

1) all probes are set to the proper type
2) wiped the EEPROM and flashed the latest firmware
3) enabled AC filtering

*with heatermeter powered off and probes removed:
4) checked the impedance of the resistors. The 10K ones were OK, but the 100K ones were off by large. All of them would read values around ~60K.
5) I cleaned the board with alcohol and a toothbrush: no improvement

6) now this is where it gets interesting. I re-soldered all the 100K resistors, and then measured the impedance. Now all of them they measured around ~97K. This in itself is weird to me, but perhaps I dont have the proper understanding of electronics. I mean, how can re-soldering change the measured impedance of a resistor when I am measuring directly on the resistor leads?

Either way, I was happy to measure them ~100K, so I figured this would have solved it. So I put everything back together, and for a short while the problem was solved. The heatermeter was displaying -no pit probe- and all other probes were not showing anything when I did not have any probe inserted. And when inserting a probe, the correct temperature would appear.

However, after a few minutes, the initial problem would re-appear.. All probes were again showing readout (now around 150F) without having any probes connected. Also, when measuring the resistance, I would measure around ~60-70K.

Each time I would re-solder, the problem would go away for a minute or 2.
And another interesting fact to mention is that the problem would re-appear instantly, if I would re-solder, and then clean the board with alcohol.

I am thinking that somehow the flux? is aiding to the conduction. And when it dissipates (if thats even possible) or when I wipe it away with alcohol, that conduction is lost. Although then you should still measure ~100K when measuring at the leads right?

I'm lost on what can be the issue, can someone help here? Thanks.
 
What flux did you use? If the flux was conductive then that would cause what you're experiencing and if that was the case then it will be almost impossible to clean off.

The only thing you can test really is to power it up and one side of the 100K resistor (the side connected to the jack) should be very close to 3.3V and the other side should be about 3.2V (the side connected to the ATmega) when you're measuring it. That's with no probes connected at all. If when you see weird temperature values appear on the HeaterMeter it corresponds to different voltage readings, then that's a problem but if the probe temperature is changing but you've got the right 3.3V voltage then that something on the ATmega connection isn't right.
 
I used Velleman SOLD100G6 which has a resin core, but I also believe I might have used S-39, which I understand now is not to be used on a circuit board..

I made the following measurements (moving from probe towards ATmega):
All measurements were made with ATMega powered up and no probes connected.

100K (probe side lead) -> Ground
0: 3.24 V
1: 3.21 V
2: 3.23 V
3: 3.24 V

100K (ATmega side lead) --> Ground
0: 3.14 V
1: 2.84 V
2: 3.00 V
3: 3.12 V

ATmega --> Ground
0: 3.08 V
1: 2.78 V
2: 2.96 V
3: 3.05 V

and the resistance I measured across the resistors:
0: 90kOhm
1: 72kOhm
2: 75kOhm
3: 91kOhm
 
Yeah the "100K (ATmega side lead)" seems bad to me. The voltage should not be pulled down that much on measurement. If you did use S-29 then there may no way of fixing it short of some industrial cleaning procedure with the proper solvent and an ultrasonic bath.
 
Fixed :)

I think ultimately what fixed it was using the right solvent. I previously used ethanol and turpentine, which did not do the trick.

Today I used 96% alcohol ketatonus. First I used a tooth brush and scrubbed the circuit board and components, then I applied a liberal amount top and bottom, basically soaking the circuit board, and let sit for 15 minutes or so.
After that, I used compressed air to remove the alcohol.

End result is that all probes now have 0 reading without probes, and the proper reading on the display with probes connected.

Now it's time to make good use of it.
 
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