DIY HarvestRight (Analog - 2015) Upgrades

Additional discoveries - so the controller inside the unit has two pots on it, these set the "window" for the heating cycle once vacuum is achieved, it appears to currently be around 500/625, I see no need to change this as the unit works great, I just want to limit the max tray temp. Just noting things here as I go. 

Update number 2, completed quite a few tasks today after taking yesterday to mow and clean up some more brush on the land that will be my future business. Anyways the updates...

Received the T-Type thermocouples and the new MAX31856 boards (SPI based chip that works automatically with basically every type of thermocouple). The headers had to be soldered but the new station made that easy enough. I also created a mounting platform for all of the components in FreeCAD and printed it (too bad I didnt have screws small enough for the 31856's, had to use mounting tape, thats why they arent perfectly flat.

Once assembled I tested some basic python using circuitpython lib to test the thermocouples and all is well there, resolution is good and accuracy seems spot on compared to other reliable sensors. I also tested running the lead wires along the power cable for a t-shirt press with 600w heater to test ac induced emi on the thermocouple signal - this worked better than expected even wrapping the leads around the power cable caused no issue. My fear was that the heaters operating could cause interference in reading the thermocouple as it uses an extremely low voltage signal, however it doesnt appear to be problematic - worst case we can always interrupt the heater cycle to check temp.

Second major milestone is I recreated the "electric interconnect" that HarvestRight used at this time - a 1/2 MNPT plug drilled for the 2 heater cables inserted in a 1/2->3/4 Stainless NPT bushing. I replaced the components and drilled the new plug for the 2 heater cables as well as the 2 thermocouples pulled through one hole (made the tightest fit due to the cables being flat). Finally I mixed the EA1C epoxy on a scale - something Ive never done before hah, but best to insure accuracy with this. The idea is this "special" epoxy has minimal outgassing and is perfect for vacuum applications. Anyways I started with trying to use a syringe to fill the joint, but it was too viscous. Ended up using a small stainless rod to "dip" the epoxy into the fitting, after a bit it settled down into the bottom and worked pretty well, just had to do some expedient cleanup.

The epoxy recommends a 72hr full cure at room temp, so well be waiting until Wednesday night to do any vacuum testing. For now theres a few things to accomplish, but I should be able to get this done tomorrow.

1) Run freeze dryer through cycles (other than truly running vacuum pump to trigger dry) so that we can capture the serial output and make a loop that detects what cycle its in when it changes, then updates the times remaining and vacuum level when applicable - well have to finish this once I can run full test cycles Wednesday, but can get most of it done now.

2) Develop a small flask app (I have some experience with flask, not a alot, its a good opportunity to learn more) that uses a template to render the current values captured from serial and the thermocouples, as well as a simple form to POST the desired tray temp back to the main python loop as a var.

3) Wednesday test it all and debug the app/webui. 

Some pics of todays work...

Got some free time this afternoon/evening and spent it (all) writing what is now called HarvestRightEnhancer lol. Basically a simple python app that captures the serial data to the display (Time remaining for each cycle, vacuum when displayed) as well as the thermocouple temps, displays it via flask, and logs it in influxdb (so we have a datalog we can look at in grafana). Finally it also controls the heater relay which the target value can be set in the webui. It really probably needs some tweaking, but so far it works pretty smooth. 

Tomorrow Ill get the fittings back in place and wiring cleaned up - then itll just be waiting until Wed evening with fingers crossed before we do vacuum testing!

Once vac testing is underway Ill be able to capture the final mode (Drying) and configure it to display properly - after that the code will be available on my github with instructions here to follow.

Im really not too worried about the seal, it seems to have filled in the fitting nicely, however I am sitll unsure if the control board uses any type of current sensing on the heater output that could trigger a fault when my relay opens the circuit. This seems extremely doubtful, and Ive certainly powered it up with the heaters unplugged, but I wont be able to fully test (send it into drying mode under 500mtorr) until the epoxy fully cures!

Worst case Im feeling pretty confident I understand the logic here and could just do away with their controller entirely 😀 (That may still be a project down the road)

I created an account just to follow this post. Love that you figured it out... inspiration for me to tear more shit apart! How’s everything going with it now? Did you figure out the last piece to the puzzle? Would also love the GitHub repo when you post it, I’m a dev so it’d be interesting to look at. Thanks for sharing your project!

Unfortunately I ran into some other issues with a bad door seal and different flare fittings sending me on a wild goose chase, so I havent updated this in a bit. Everything from the mod side is working smoothly and has been tested for several cycles now, I added some pulse functionality like what the scientific models have in dry, I meant to add those settings into the flask ui and just put settings on a separate tab, was going to try to get that done before I posted it. So maybe this week! And thanks for the interest!

Is this thread still updated?