Thermocouple Board Success (sort of)


 
The v4.1 thermocouple board isn't used, it's all on the main PCB now so you can save that for some other thermocouple project! The v4.2.3 boards went out on May 19th so figure Jun 2 for them to come in, then 3-5 days shipping. I'd be happy to try and send you one, this time in a padded envelope so hopefully it won't get shredded. I've got a couple of ground plane changes as well as silk fixes and whatever errors I find once I get them so there will probably be another set anyway.

I'm not 100% sure about the DISABLED probe concept. I need to spend some time thinking about how it would affect things all the way through to the webui. I'm kinda weary of it because the "big" probe display (the one on the top of the home page) will read OFF in that situation, and any alarm setup won't follow the control probe which is inconvenient. I just need to think on it some more but don't worry, you've got some time :)
 
Oh, I was kinda thinking when you set Probe0 to disabled then Probe1 would be substituted for Probe0 straight across the board. Meaning it would now be for all intent and purpose Probe0 and show on the big pit temp display and assume all the alarms for Probe0 etc, and it would be Probe1 that actually ends up missing. Don't know if that is a big deal programming wise or not.
 
Initially, because of reading how finicky a thermocouple may be about the connector etc, I wrote off the idea of using it over the CAT5 cable at all. Now that I've ordered the thermocouple and am actually thinking about implementing it, I've got to wondering, if I put the thermocouple circuit in my roto damper and run the output though the CAT5 cable (rather than the raw thermocouple signal), perhaps it might work? What do you think?
 
Bryan Mayland said:
It is possible, but the thermocouple is roughly 3 times more sensitive to noise than a thermistor probe.
Click to expand...

Don't you think the post electronics signal from the thermocouple would be less sensitive to noise than the raw signal, and capable of pushing the signal down a longer wire?
 
It's a low voltage constant signal going down a long wire it's going to pick up noise the same as any other wire. I hesitate to call it a signal because it is just a constant voltage sitting on a wire that changes very little (except over a long period of time). The output impedance of the amplifier doesn't really matter, you can't out "gain" noise by pushing more current, what matters is how much the wire acts like an antenna. It is more sensitive to noise because 1mV of noise on the thermistor is around 0.1F but 1mV of noise is 0.36F on the thermocouple regardless of reference.
 
After having 2 of my 4 probes go belly up this weekend during a smoke, I am ready to build another HM with Thermocouple support. Stupid Maverick probes when they failed on me doubled the temp as opposed to dropping to 0, so I had a good 1.5 hours where I thought my pit was 330F when in reality it was close to 150F and dying. Oof.

In the mean time I stocked up on probes so I don't get caught during a smoke with non functional probes..
 
Yah, I'm in the same boat with you Kyle, sick and tired of burning through Maverick probes. They are just so damn sensitive to moisture and the 700 degree top end limit on their "high heat" probe just isn't enough for my high heat cooking. Last week I burned up a brand new one on a pizza cook during the very brief temperature spike after having the lid open a bit, really P'd me off....
The Thermoworks probes seem more resistant to water but they don't have anything for high heat cooking (the high end on their high heat probe is even less than the maverick). I think once I get the thermocouple in place to control the pit I will be running Thermoworks for food probes and should be pretty happy with that...
 
Have you posted the latest version of the thermocouple driver schematic anywhere yet? Is there any reason I can't use it on a HMv4.0?
My thermoworks thermocouple should be here tomorrow and I would like to start experimenting with it if possible. I guess the high temp thermocouple I ordered through Amazon is a slow boat from china deal, it wont be here for a while yet. I wish they would indicate somehow when items are located off shore...
 
I got the ThermoWorks thermocouple today and it looks really great, I am impressed by the construction and material, it seems like this thing will be able to handle the abuse I will be throwing at it... I see what you mean about it being long though, I think if I end up permanently mounting it in my "FauxMado" I will poke it though a hole in the hood like the regular thermometer and bend a right angle in the probe so it shoots across inside the top of the lid. I got the thinner of the two because I figured I would have to bend it after your comment about the length, the 1/16" thick probe is gonna bend easily and thermoworks says it's bendable, so that should work out pretty good I think.....

...but I need to get a thermocouple circuit built up here and do some testing before I drill any holes in my "FauxMado", so I am anxious to get going on that. I'm planning on doing some tests running the thermocouple driver on the damper end and sending the post driver thermocouple "signal" down the CAT5 cabe to see if that is doable or not. I've done a little searching/reading about thermocouple amplifiers, they do exist, so that is encouraging me to experiment with this concept a bit. I was hoping to get a look at the thermcouple driver schematic and if it's not too complicated I might try to source and order standard size components (as opposed to SMD) and piece together a test circuit without a circuit board that I can use for experimentation.

If that does work out I've been thinking of adding another optional part for the roto damper that would house the thermocouple connector and circuit which would press fit into the wiring cavity opening that is there now. This would close off the bottom side of the roto damper, which a few people have asked about already, and add thermocouple support, so I am pretty excited about the possibility that this may work out...
 
Last edited:
Did you get the email I sent? It has the schematic but you need to add the output filter if you build just the thermocouple part standalone. There is no non-SMD AD8495 component, but the rest of the parts can be had in through-hole. Unfortunately the AD8495 is the only challenging one to solder.
 
No, I never got the email? Just sent a test message to myself and it was delivered, so not sure what happened with yours...
 
Bryan Mayland said:
There is no non-SMD AD8495 component, but the rest of the parts can be had in through-hole. Unfortunately the AD8495 is the only challenging one to solder.
Click to expand...

OK, so maybe I'll grab a couple of these SMD to DIP adapter boards to solder the AD8495 to and can use that as a base to build by experimental circuit onto. Hopefully with a little searching I will be able to source those boards in the USA as opposed to those from Thailand in the ebay link I posted... Or maybe I will just order some extra thermocouple boards of your design from OSHPark? Though I think it might be more experimental friendly if I go the SMD to DIP route and build with normal size components...
 
Check your spam folder I guess. It went the first time but I just sent it again to be sure. The mail server accepted it:
Code: 
Jun  3 18:43:06 nixon postfix/smtp[13777]: 71848600F05: to=<your email>, relay=mx3.hotmail.com[65.55.92.184]:25, delay=2.3, 
delays=0.75/0.01/0.72/0.85, dsn=2.0.0, status=sent (250  <538E4F77.3050601@leoninedev.com> Queued mail for delivery)
I think I might have one of those thermocouple to 3.3V/GND/Signal boards lying around. If I do I can include it. If you can solder the AD8495 to the board the resistors and caps are a doddle. You put some solder on the pad, heat it up and place the component in it. Remove the soldering iron and let it cool and then just touch the other side. Super easy.
 
Last edited:
Bryan Mayland said:
I think I might have one of those thermocouple to 3.3V/GND/Signal boards lying around. If I do I can include it. If you can solder the AD8495 to the board the resistors and caps are a doddle. You put some solder on the pad, heat it up and place the component in it. Remove the soldering iron and let it cool and then just touch the other side. Super easy.
Click to expand...

You're right, I do have the thermocouple board from my HMv4.1, but I thought your current circuit was different?
 
Oh yes, it is different than the v4.1 TC board. I have a v4.2.1 TC board which has all the proper filter components and is in the shape of the TC jack. It is easier to solder because it is like 3x the size or so. The v4.2.3 is a little different as well, because the output lowpass filter is the one that's on all the jacks now (which is through hole and not SMD).
 
I have some of the thermocouple boards that were at one time meant to be added on to the 4.1.2 ? boards, that I worked on with Bryan.
I can send you a couple if that will help, call it a breakout board for the AD8495 with screw terminal and/or the proper themocouple jack.
By removing the pull-up resistor you can add the output of this board to the a/d input.
 
well, damn, too many options at this point, I also ordered some MSOP-8 to DIP-8 conversion boards on ebay cause they were just a couple bucks and should have them by the end of the week.
I guess I want to go whatever way will make it easiest for me to build the circuit Bryan is working on....
 
Bryan Mayland said:
It's a low voltage constant signal going down a long wire it's going to pick up noise the same as any other wire. I hesitate to call it a signal because it is just a constant voltage sitting on a wire that changes very little (except over a long period of time). The output impedance of the amplifier doesn't really matter, you can't out "gain" noise by pushing more current, what matters is how much the wire acts like an antenna. It is more sensitive to noise because 1mV of noise on the thermistor is around 0.1F but 1mV of noise is 0.36F on the thermocouple regardless of reference.
Click to expand...

The noise you talk about should be taken out in the AD8494. Looking at the spec for the amp, it says "For best accuracy and CMRR performance, the setpoint voltage should be created with a low impedance source. If the setpoint voltage is generated with a voltage divider, a buffer is recommended." I looked everywhere for the schematic to see how you are creating the setpoint voltage but couldn't find it. Maybe I need more coffee, then I'll find it.:confused:

The CMRR is noise, so, the better the setpoint voltage, the better the noise filtering should be.
 
You must log in or register to reply here.

 

Back
Top