Thermocouple Board Success (sort of)


 
yes, it is odd, cause during the slow initial warm up of the grill it went up to 700 smoothly without issue, but when the fire was smoking hot and I closed the lid the temp SHOULD have shot up rapidly and overshot 700 by a bit, but it never even showed the upturn on the graph. Maybe the rapid transition from bandgap to full 3.3v reference freaked the HM out somehow? I don't really know what is going on under the hood with all this but it seems it was only reading the thermocouple in the bandgap range going up and coming down, everything above the ~400 degree range was missing... even though it did register temps up to 700 degrees when the temp was rising slowly....
 
The transition between the two is always "rapid" and switches back and forth every second in normal operation. That's the only software thing I can think of that happens around your problem area. The only thing I can suggest is that you measure the voltage leaving the thermocouple amp when it happens and measure the voltage at the atmega ADC input and see if they are saying it is 300F or 700F.
 
OK, well, using the onboard amp at this time, so I would have to pull the HM out of the case to measure when this happens, but that's no problem.

"see if they are saying it is 300F or 700F" Exactly how will it be saying that? I assume in the over 400 degree range it should be reading 3.3v and under it should be reading something else? I really don't know what I am looking for here so a little more guidance would be helpful....
 
Ah gotcha. I thought it was over the cat5 extension cable or with your breakout board.

The expected voltage you should see is the temperature in Celsius * 5mV.
300F = 149C * 5 = 0.745V
700F = 371C * 5 = 1.855V

I'm going to pick up a giant strip steak for dinner tonight for "Testing" purposes.
 
Yah, since the thermocouple amp is the onboard one the voltage at it's output should be the same as at the ATMEGA.... but I will still measure it to get some concrete data on what is going on....

I am still confused about the bandgap vs 3.3v reference though, does that happen in the thermocouple amp or the ATMega?

The only other thing I can think of is possibly the heat radiating from the grill might have increased the temp of the thermocouple to panel jack junction to flake it out, but that is highly unlikely 'cause it is hanging down outside of my roto damper quite a bit and I don't think it would be warmed at all under any condition there, and the timing of when the probe dropped off was exactly when I closed the lid and the thermocouple temp shot up like a rocket.....

EDIT, to be clear, I have been using the thermoworks thermocoupe over the long cat5 cable sending the (+) down one lead and the (-) down another, and using the amp on the HM board. It has worked well for me this way on several lower temoperature cooks (and when the temp went up slowly to 700 degrees).

Next time it happens I will take a voltage measurement at the output of the thermocouple amp, then power cycle the HM, if the thermocouple does not reappear I will move the HM out to the grill and plug the thermocouple directly into the HM to eliminate the CAT5 cable as a possible source of the issue.
 
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I tested high temperature transitions tonight, going up to 650F and opening the lid until it drops to 300F (which requires me to actually put a sheet pan in the way to get it to drop that low) and back up again. I did the test 4 times and never experienced any sort of anomaly even using my highest noise power supply and a thermocouple with a conductive braid. It also worked ok on the slow transition from 600F to 200F as the grill cooled over an hour.

I can't reproduce it at all so unfortunately you're going to have to crack the case next time it happens. I am almost completely certain it isn't a HeaterMeter problem.
 
OK, good thing I have the easy open sliding back case! LOL

I was dealing with HIGHER temperatures when this happened, pit was at 700 (and fine) and the thermocouple flaked out when I would have expected a spike of overshoot above 700 after having the lid open.

I was just about to start another high temp cook to try and reproduce this situation but was also trying to fix up the MOSFET servo booster at the same time but have been unable to figure out what circuit I should have in place there.... see my recent post in the servo booster thread for more details on that....
 
Did another high heat cook tonight, was able to make the probe drop twice more in similar circumstance...
I was running things with my voltage meter on the thermocouple amp output, each time when it happened the voltage output from the amp was right where it was supposed to be (similar to before the probe dropped off), between 1.500 volts and 1.900 volts for pit temps from say 300-700 degrees. I power cycled the HM and both times the probe was registering when it powered back up, so I wasn't able to take the unit outside to test with the thermcouple plugged directly into the HM. (and it was off and on raining so I didn't want to take the HM and my expensive Fluke meter outside)
I will try the next high heat cook on a clear day with the thermocouple plugged right into the HM and try to reproduce this, but since the voltage output from the amp was reading right I'm still wondering if the software is glitching out on something...
 
This seems like it's going to have to be something I'll have to see to understand what's going on. The only other thing I can think of is that there's so much noise or something that it's not flipping to 3.3V reference because the average is artificially below the threshold due to the noise.

1.5V is 572F though, which is way more than 300F and way above the switch threshold of around 1.0V.
 
300-700 degrees for 1.5-1.9 volt was just a ballpark estimate, cause temps are very fluid when closing the lid on a fire that hot. I think 750 degrees was roughly 2.000 volts. At any rate, the HM was reading temps accurately with those voltages at the amp output, and then it wasn't when I ran into the issue. Could be noise, not really sure, the next cook with the thermocouple connected directly to the HM will tell the story.... or perhaps I should get the firmware installed that will show me the noise? What baffles me is why the thermocouple registers fine after I power cycle the HM? You would think if noise was the issue the noise would still be there after the power is cycled?
 
Yeah the reboot thing is what really throws me. On startup, the default reference is 3.3V so if it were "stuck" on the bandgap then that would effectively unstick it. I can't think of any way that's possible though unless the average voltage is below 1000/1024 * 1.1V = 1.074V even though the output should be around 1.5V as you measured. If there's 800mV (288F) peak-to-peak of noise then that's insane.

If you're running the latest LinkMeter package then I can send you an AVR firmware with the noise graph turned on and maybe that will shed some light.
 
Hello!

I have "found" some Transmitters for Thermocouples (http://pma-xtra.de/en/products/ci45.html). They generate e.g. 4..20mA Signal. Together with a shunt it is possible to generate a voltage drop U at the input of the heatermeter. Is it possible to implement coefficence (a and b) for a linear function between temperature and voltage like T=a*U+b. Probably for ur thermocouple board u need more or less the same functionalty!?

BR

Holger


PS: For sure the pullup resistors are not equiped
 
I know you (Bryan) said you thought the Thermoworks High Temp Thermocouple was a bit long (at 7"), and I initially thought that too... but I have been using it at grill level, inserting it so the threaded portion and cable are outside the grill and the long probe sticks into the grill nicely at grate level for nice high temp grate level temp control. Since I ordered the extremely thin 1/16" probe it's even smaller than a typical probe lead and easier for the gasket to seal around, so I've gotten to like the extra length on this thermocouple....

Doing steaks at the perfect 750F temp, without burning up your probes, NICE!
 
I was thinking about trying that one, was not sure how I could mount it center about a inch below grate. I bought the Auber probes that have a clip for easy mounting on the grate
 
John Bostwick said:
I was thinking about trying that one, was not sure how I could mount it center about a inch below grate. I bought the Auber probes that have a clip for easy mounting on the grate
Click to expand...

The clips are easy, but I am unaware of any type of cable that can stand 700F+ heat from a fire directly below it? So, unless I am missing something, the Auber clip probe lead would have melted just like a thermistor probe if used at grate level for high heat cooking?

That was the reason why I was commenting on how the length of this ThermoWorks Thermocouple ended up to be a plus, because it is long enough to extend into the cooking area at grate level while leaving the lead wire outside of the grill... To secure the probe in place I have some small metal clips (that come on the coffee bags my friend sends me from Hawaii), which work for me just about as easy as having the clip built onto the probe....
 
RalphTrimble said:
The clips are easy, but I am unaware of any type of cable that can stand 700F+ heat from a fire directly below it? So, unless I am missing something, the Auber clip probe lead would have melted just like a thermistor probe if used at grate level for high heat cooking?

That was the reason why I was commenting on how the length of this ThermoWorks Thermocouple ended up to be a plus, because it is long enough to extend into the cooking area at grate level while leaving the lead wire outside of the grill... To secure the probe in place I have some small metal clips (that come on the coffee bags my friend sends me from Hawaii), which work for me just about as easy as having the clip built onto the probe....
Click to expand...

Yeah, I too would like to keep the wire part out also. But I want the probe to be in center, and be able to bend it out of the way to remove the charcoal basket. The 7 inch probe would not get to center, a 12 inch would be great, but I believe I saw one but out of my price range.
 
So we are talking apples and oranges then, cause I was commenting on how the 7" probe is good for high heat cooking, and your requirements are obviously not for a high heat scenario if you have your cable inside the grill... I find the 7" probe sticks into the pit far enough to read the grate temp for high heat cooking just fine... and btw, it is bendable if you need that, though I am just setting the probe in place so I can remove it if I need to get at the fire box below...
 
Wow. I started soldering all the parts on my HM v4.1.4 board yesterday as a warm up for tonight... my first attempt at soldering anything as tiny as SMT.

The tiny parts are all on there, but most of the joints look cold and I cant even tell if there is any bridging.
Is it possible to re-flow everything by putting the whole thing in a toaster oven ? (if yes... what temp? how long ?)

Any chance of getting these boards with solder paste applied to the pads ?
If the solder paste was on these, anyone with tweezers, a magni-visor and a toaster oven (and really steady hands) could probably make one.
 
The best way to solder the amp is use lots of flux and putting a dab of solder on one pad to use to help line up the amp and hold it from moving. THen once you have the part lined up add solder to the other side, don't worry about bridging it, in fact its ok to bridge it the more solder the better to a point. repeat for the other side. Then take a solder wick and remove the excess solder form the amp. Only the solder that's between the connectors will be removed and you are left with a perfectly soldered part.

The hard part for me is lining up the part, even with magnification, my eyes get blurry , after a bit.

After soldering check with a multimeter. If you have bridges still then you can try to apply the solder wick and if that does not work adding more solder and flux and then solder wick it again should remove the bridges.
 
I did all my SMD work with a regular old Radio Shack 40W soldering iron, wearing a magnifier visor with flux applied to the board. I would have preferred using a flux pen but the only place local is Radio Shack, they had flux in a tub which I applied to the board with a q-tip. I've done 3 SMD thermocouple amp chips now and haven't had a failure. With the mag-visor I can pretty much see if there is a bridge, then I confirm with a multimeter. The center two pins on one side and outer two pins on the other side have a trace between them (are bridged by design), so you only have to worry about isolating those other pins...
 
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