More ET-732 blues


 
C

C. W. Robertson

New member
Greetings:

I have one of the Linkmeters put together. I ran into some probe problems, so I took a broke probe and attached a Vishay Thermistor. That worked great, and it worked on all four channels. No problems. But when I use the ET-732 probes (and pull them back so they make contact correctly) the probles are all turned off.

I did connect a 1M linear pot aross the pit input the probe, but it still couldn't see it. Even when I made slow changes.
So that make me think that maybe the coefficents were off for the ET-732 probes.

This is the table of temps and resistance I've got for my ET-732 probes:
82 F 0.891 Mohms
104F 0.488 Mohms
145F 181.7 Kohms
165F 116.5 Kohms

and the coefficients loaded are
5.36924e-4
1.91396e-4
6.60399e-8

I'm using 10K resistors on the heat monitor board. And based on a search on the fourm, I've checked the resistance values on the board, it looks good.

So, couple of questions.
Is the restance table reasonable for the ET-732 probes? They do work in my et-732 meter, so I'm thinking that are correct.
Are the coefficients correct?
What elese should I check?

-Thanks.
 
the T/R numbers look good to me.

Did you use the ET-732 presets for the coefficients? I don't remember them off hand. Even if they are off you should still read some temperature.

dave
 
Can you copy and paste the info below the 'Full configuration URL' line? Those settings are correct, I just want to see if they applied correctly.
 
Yes, I used the presets. I was thinking I should see some temps, unless they were out of range. Can you point me to the equation the coefficients are used in?
-C. W.
 
al=40,200,40,200,40,200,40,200 &fn=10,95,0 &lb=100,255 &ld=6,240 &pc0=0.00053692398,0.00019139599,6.6039896e-8,10000,1 &pc1=0.00053692398,0.00019139599,6.6039896e-8,10000,1 &pc2=0.00053692398,0.00019139599,6.6039896e-8,10000,1 &pc3=0.00053692398,0.00019139599,6.6039896e-8,10000,1 &pidb=4 &pidd=5 &pidi=0.005 &pidp=3 &pn0=Pit%20%20West &pn1=Pit%20East &pn2=Food%20West &pn3=Food%20East &po=0,0,0,0 &sp=175

And I just plugged the coeffients into the S&H equations and they gave me the temps within a degree:
A 5.37E-004 5.37E-004 5.37E-004 5.37E-004 5.37E-004 5.37E-004 5.37E-004 5.37E-004
B 1.91E-004 1.91E-004 1.91E-004 1.91E-004 1.91E-004 1.91E-004 1.91E-004 1.91E-004
C 6.60E-008 6.60E-008 6.60E-008 6.60E-008 6.60E-008 6.60E-008 6.60E-008 6.60E-008
R 891000 488000 375000 225000 181700 132000 116500 110900
“1/T 0.0033288839 0.0031922405 0.0031330552 0.0030192686 0.0029720383 0.0029018349 0.0028745235 0.0028637723
T (K) 300.4009855073 313.2596099264 319.1772705737 331.2060433721 336.4694161866 344.6095466699 347.8837453372 349.1897752143
T ( C) 27.4009855073 40.2596099264 46.1772705737 58.2060433721 63.4694161866 71.6095466699 74.8837453372 76.1897752143
T (F) 81.3217739131 104.4672978676 115.1190870326 136.7708780698 146.2449491359 160.8971840057 166.7907416069 169.1415953858

Actual (F) 82 104 115 136 145 160 165 169
 
Yep, configured correctly. You've got me stumped. The test probe with the vishay works fine with the correct parameters so the circuit appears ok, The 732's are providing the correct resistance. Don't know what it could be.
 
You can try setting the probes to Resistance mode and see what numbers you're getting.

Plug the probe into any jack besides the Pit jack, and enter "0R" for the setpoint on the configuration page. Now when you go back to the home screen the probe value will be in ohms.
 
I just built my heatermeter this weekend as well and was using ET-732 probes and having similar problems where it wouldn't register the probes as plugged in. Interestingly, if I powered it through the Raspberry Pi via the USB cable they worked mostly, they would drop in and out at room temp. If I powered it from the power supply recommended in the list then it said no probes however the voltages at the probes matched up on each. Sometimes if I touched the ethernet jack, plugged in an ethernet cable, or touched the HDMI housing it would then come on and others it wouldn't. The power supply was putting out 12.4v so it appeared to be fine. I even desoldered/destroyed the optional 3.3v regulator to take it off thinking somehow that was related but it's removal didn't make any difference. Seemed like there was some odd grounding issue somewhere. Ended up switching it out with a 12v 2A power supply I had laying around and it worked more often then. Needless to say I pulled a probe from my old OXO thermometer and it seemed to work with the Radio Shack settings so I used that for my smoke instead. I've now ordered some ET-73 probes from Amazon hoping those will work better.

Do your probes have continuity between the shielded cable and the shield on the jack, it's the section on the jack that's not the tip. Mine did not and I saw posts from others claiming there's do so that may have something to do with our problems.
 
Thanks for the help. Here are a few more pieces to the puzzle....

I did replace the 10K R17 to the pit input with a 100K pot. One leg to gnd, the other to 3.3, the center tap to pin 28. I wanted to see what voltage would be converted to what temp. And to see what the temp range was that could be displayed using the et-732s.

I ended up with the following table:
temp voltage
254 2.3
400 0.74
245 2.40
269 2.13
252 2.33
307 1.656

Since the HM board uses 10K, if the probe is at 10K, the voltage should be 1.656 at pin 28, which should give a temp of 307. Which it does.

The odd thing here is if the voltage going to pin 28 was less than 0.074 ( >400F) or greater than 2.40 (<245F), the display says -No Pit Probe-

I did change the setpoint to 0R and plugged in a probe to Food1, Food2, Food3, and all I got on the LCD was Pit: 0 (degree symbol) R^ 0%^
The web page says they are all off.

Any ideas?
 
That's a great test you came up with there. I'm stumped though. I can't imagine why it wouldn't be able to measure any value >2.4V. The only thing I can think of with any significance is that that's close to VCC - forward voltage of a diode (@0.5A though).

Have you tried running the HeaterMeter in standalone mode? Just disconnect it from the rPi and wedge the 3.3V regulator into the IC4 holes. That could eliminate some parts of the equation at least.
 
I have 2 normal et-732 food probes and 1 et-732 pit probe. Here is my result:

3probes_zps1d4f74ba.jpg


The ambient is the internal temp sensor.

I have a 12v 1A power supply connected to the HM4 board.
 
Last edited:
Thanks for the responses.

It's not working yet, but I'm seeing some signs of life. Re-checked the diodes and the caps. Touched everything with a soldering iron, Everything looks gook. IC4 is not populated cause I'm using it with the pi. I did populate the FET, but I don't plan on using it. Re-imaged the cf card. I did swap AVR chips and another pi. No change. I used an old Weber probe and figured out the S&H constant, put them into the web interface. No change.

But I did notice something odd. Cycled power (unplugged the adaptor from the HM for a while, and then plugged in back in). And, for just a about half a second, it gave me the temp the Weber was reading before it said -No Pit Probe- or blanked the display on Food1, 2 or 3. This happens well before the IP address is displayed on the LCD. And it never comes back unless you cycle power.

I'm sure something else is wrong, but it's like the code is displaying the first result, checking to see if it is in range, determining that it isn't and then blanking the displays, except for the -No Pit Probe-.

I'm starting building number two now, but I was wondering about diagnostics. Is there a way to put this into a diagnostic mode to simply display on the LCD or web the voltages going to the AVR from the probes or disable the limits to turn the probes "off"? I think it would be very helpful.

Thanks.
 
The debug mode is setting the 0R setting that you tried. When you did that it looks like you go a zero ohm reading, if I read your post correctly. It is easy enough to download the code and edit it if you're into that. You need to have the Arduino IDE installed first.

dave
 
The Voltage is never calculated, which is why the resistance is output instead. If the Resistance is 0 (the ADC is reading MAX or 0), then it won't be shown. Note that the Pit probe will not switch to resistance, only the food probes do (the pit probe switches to celcius in resistance mode).

I would suggest again disconnecting the HeaterMeter from the rPi, take IC4 and put it in the IC4 holes (don't solder it) and power up the HeaterMeter. See if it works ok standalone. If you have an FTDI cable you can power up the HeaterMeter without IC4 if I remember correctly, so there's another option.
 
Thanks. Disconnect rPi, insert IC4, power up. Same behavior. Didn't see the temp flash, just went right to No Pit Probe. With the 0R setpoint, the LCD says Pit :0 degrees F.

No change. 2nd build complete with the same issue (so at least it's repeatable).

Thanks.
 
PS Just for grins, I went back and checked the expected voltage at the AVR for the et-732 probes given R18, R17, R16 and R5 of 10K and room temp (~1.29 e6 ohms) . It looks like it would be hanging close to the 3.3 rail, so I changed R18 to 100,000 ohms, changed the R on the web configuration page. Saved and powered everything back up. I still have No Pit Probe, but I have 2.8 V between 28 and 22 on the AVR.
 
I got my et-73 probes in today and they work like a charm not to mention being able to plug them in all the way. Were you able to find one to test C W? Got a 2 pack on Amazon for $20.
 
Hi There. I got the Maverick ET-72/ET-73 High Heat 6ft food probes, plugged them in and it took right off. All four channels, no problems. I'd like to understand what the issue is with the 732 probes, but "that's another problem for another day". What a cool project!
 
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