Thermocouple Board Success (sort of)


 

Bryan Mayland

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Ideally it would be an addon to the HeaterMeter v4.1 board that somehow fits in the same footprint as the existing board. That's why my design is so constrained, because the 4 input version would need to be 0.5" x 1.4" and also not short out any of the connections on the board below it. The big holes on my TC board overlay the big holes on the HM board and make connections to the HeaterMeter.

I'd like to see what you come up with though!
 

Alan Erickson

TVWBB Fan
Yeah I'm aware of the different types of junctions. You don't get much of a choice though. Check Thermoworks's and Auber's web sites for their list of thermocouple probes and tell me which are grounded and which isolated. You just sort of get what you get.

They make them. It's just a matter of whether we can get them for a price that we think is reasonable (if that's what's needed) . Also, the choices for the protective braid over the wire get limited with the higher temperature rating. Typically some kind of glass cloth instead of nice clean ptfe. Here are a couple of undergrounded probes that are around $50. Not sure if it's possible to find something in the $25 range or not.

http://www.coleparmer.com/Product/Type_K_High_Temperature_12_L_040_diameter_thermocouple_probe_with_stripped_ends_ungrounded_junction/EW-93631-42

http://www.omega.com/pptst/TJ36-XCiB_chb.html

I'm assuming that the pit probe would be the only thermocouple and that the meat probe(s) would still be thermistor?
 

Bryan Mayland

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It could be however you want to set it up. Probes are a personal choice I know but I'll probably be happy with my ~$10 exposed junction deals. I might put a tiny blob of thermal epoxy on the tip just to protect it. For a pit probe anyway.
 

Frank Giacinto

TVWBB Member
I was not aware of the stacking and the space constraints, I will order a pi and a 4.1 board and take some measurements.
Are the 4.1 boards available in singles?
Meanwhile I will work on a single channel board and then expand to a multi channel board.
 

Bryan Mayland

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They're not yet available in singles, but you can get all the dimensions you might need from the EAGLE board layout in github. Space constraints aside, creating a thermocouple to analog voltage conversion board is as simple as following the datasheet reference design it seems. It's squeezing it into a tight place that makes it fun, like using the cutout from the HM4.1 board to actually hold the optional thermocouple board, making it an all-in-one setup, apart from wiring it to the panel connector.

EDIT: Also the issue of cost. I didn't want the thermocouple circuit to end up costing more than the whole device.
 

RalphTrimble

TVWBB Diamond Member
Bryan, have you done any work on adding the filter components to the thermocouple board yet? I was thinking of ordering 3 boards from OSHPark and would be glad to sell one to Frank, but would prefer to get the gen2 thermocouple boards with them if possible....
 

Bryan Mayland

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It is on the schematic, an AD8495 and 0806-sized caps and a resistor from just about anywhere. The resistor isn't needed if your probe is grounded I'm told, but yet to verify.
 

Tom Kole

TVWBB Pro
It is on the schematic, an AD8495 and 0806-sized caps and a resistor from just about anywhere. The resistor isn't needed if your probe is grounded I'm told, but yet to verify.

0806? On mouser's site I'm finding 0805 or 0808 depending on in or mm but no 0806.
 

Bryan Mayland

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Hurp typo. Yeah, 0805 is the right size.

I will also say that Frank and I are going back and forth over email about a more complete solution if you're looking to go all-thermocouple. The current boards work ok for single channel, but you have to run a few wires to the panel connector and to power and output.
 

Tom Kole

TVWBB Pro
Hurp typo. Yeah, 0805 is the right size.

I will also say that Frank and I are going back and forth over email about a more complete solution if you're looking to go all-thermocouple. The current boards work ok for single channel, but you have to run a few wires to the panel connector and to power and output.

I figure since I have the boards, I'll try it out. Besides, I don't see why I would need a thermocouple for my food unless I was trying to burn it. However, if a more complete solution is designed I'll probably make one of those too just to try it out.
 
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RalphTrimble

TVWBB Diamond Member
Bryan, I had asked a while ago but don't recall getting a reply.....

Does that Model: 113-420/425 Thermoworks Thermocouple I linked you to a while ago mate up with the connector you have chosen for the Heater Meter?

I burned up my LAST Maverick High Heat probe last night while cooking some pizza, I am so sick and tired of dealing with these probes melting and freaking out from getting wet.... I need to make the move over to a thermocouple so I can put an end to this nonsense. In the summer I do high heat cooks a couple times a week and want to be able to do this without worrying about burning up the pit probe. Otherwise I will be doing my high heat cooks without using the Heater Meter, which would be a shame...

Also, what do you think of the idea to add a "DISABLE" option for Probe0 in the Heater Meter config? I think that would be the easiest way to do it "right". It's a simple, clean, easy to understand solution to allow choice between running the pit via thermocoule or standard probes. When Probe0 is disabled you could have it indicate "Probe1 is now the Pit Probe", which would make it exceedingly clear so you don't hear from people asking what's going on. You wouldn't have to rearrange the probes in software other than to make the Pit Probe read from Probe1 rather than Probe0.

I ask this, again, because once I install the thermocouple board onto my Heater Meter I lose the ability to run the pit over my CAT5 cable, which I do a LOT. If I could disable the thermocouple (Probe0) that would be a good solution.

Otherwise, the only other solution I can come up with is to rig in a regular switch between the probe0 trace that I cut and wire the thermocouple to one side and probe1 to the other... and then I would have to also wire in the pullup resistor to switch in and out as well... and I am not sure if having the switch inline with the thermocouple will play hell on its readings??? I would much rather have the "DISABLE" function available via software....
 

Bryan Mayland

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Yeah the connector is a standard "mini" thermocouple connector so any mini plug will fit. It also works with spade plugs but you have to snip off half the spade with a pair of wire cutters. Still, because the plug is so tight, they stay in just fine. Solid bare wire (like that found on the bare Auber model) also fit but they can fall out kinda easily.

I also have been thinking about the "pit probe" selector as well. I think if I just change all the verbiage to regard them as Probe0, Probe1, Probe2, and Probe3 then have the UI just designate a "control probe" which changes their order by putting that one first, followed by the other 3 in order. That shouldn't be too complicated right? Well crap they'll be misordered on the conf page... I'll keep thinking about it.
 

RalphTrimble

TVWBB Diamond Member
Thanks for the reply, I am gonna order that thermoworks thermocouple with the connector now. I still gotta get a thermocouple circuit together. I have one of the thermocouple boards from HMv4.1, but I think that is outdated and not gonna work? Have your latest set of HM boards arrived yet? Any chance I could get one when they come? I would be glad to build it up and test it out....

I really think just the "DISABLE" option for Probe0 will work fine? It wouldn't require you to reassign any probe names and would be really easy to understand. You could grey out the Probe0 data fields on the config page when it is disabled and have it say "Probe1 is now the Pit Probe" and that should just about cover it...

What do you think about that idea?
 

 

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