I wanted to share some of the progress on the device I have put way too much time into as as short project this last week.
This is the progression of my discussion over here on reading thermocouple temperatures
🌡️ Thermocouple connectors and adaptors - any to be found?
GOAL Have a custom thermocouple reader that can show me multiple temperature readings as a time series of data points.
It works now, at least the key features are there. It’s still pretty bodged together, as you can see below!
I like that the box does what I wanted it to do in terms o allowing me to see the screen either flat, or upright if I open the box lid and prop it open with a notebook.
PICTURES
Screen mounted to the box lid, showing a time series scatter plot of the temperature off the thermocouple. I grabbed the measuring tip of the thermocouple to show you some deviation in the horizontal line of blue dots.
Side on so you an see how the slot for the screen is created from 3 layers of laser-cut plywood, glued / screwed together
In the lid-propped-up configuration if you want to change the screen viewing angle
One of the thermocouples. The bare wire ends are connected to the Raspberry Pi thermocouple reader device, and then I use a female plug adaptor to connect to the male plug adaptor that is on the same bit of wire as the measuring tip. The male-female adaptor pair is necessary here since the thermocouples I want to read will be glued in place / attached to some device - I want to be able to come along with this box, pick up that male pin connector, and plug it straight in to begin seeing temperature readings.(Pic in the parts list below.)
Looking inside the box, where I have stuffed the Raspberry Pi into a box from a Rasapberry Pi mouse so I have something I can stick down. The Pi connects to the screen via a HDMI <> mini HDMI cable.
PARTS
- Raspberry Pi - I think it’s this model: https://www.raspberrypi.com/products/raspberry-pi-2-model-b/
- Thermocouple HAT reader: https://thepihut.com/products/eight-thermocouples-daq-8-layer-stackable-hat-for-raspberry-pi
- Thermocouples: https://uk.rs-online.com/web/p/thermocouples/3630250
- Thermocouple extension wire: https://uk.rs-online.com/web/p/thermocouple-extension-wire/3630389?searchId=3de26fd8-0871-4b99-9ec6-7b5194dff9e2&gb=s
- Thermocouple connectors: https://cpc.farnell.com/labfacility/im-k-m-lcf/connector-mini-t-c-line-pair-type/dp/SN35948?CMP=e-email-sys-shipping-GLB-Product
- Screen: https://www.ebay.co.uk/itm/196507103794
The box is the box the screen came in, it’s held in place with some glued-together pieces of the SLMS 3mm thick and 4mm thick plywood. I found an old micro USB power cable to power the Raspberry Pi, and the screen draws it’s power off of it in turn via USB C. The fasteners are M5 screws and hex nuts that I bought from Amazon.
INTERESTING MAKING EXPERIENCES
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If you read the other thread linked, about thermocouple reading, you will realise that initially I did not understand how they worked. Later on, I got the point that the metallurgy of the + and - wires matters, hence why I purchased the special wire from RS versus trying to just use some copper from around the space!
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I made the outline to laser cut into the plywood EQUAL to the outline of the screen I had measured. I hoped the laser cutting itself would introduce enough clearance for a nice ‘slotting in place’ fit - unfortunately it was a bit tight, so I had to carefully RE-CUT the pieces of plywood in the laser cutter, trying to line features up by eye. This didn’t work very well, as you can see in the photos.
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Most of the pain was in (1) stripping away insulation on the thermocouple wire, as it is too small diameter to work in any of the wire-stripper hand tools I could find. Instead, I had to use a scalpel and pull away the insulation I cut loose by hand. This was a pain! Also, (2) getting the code that shows the chart to run AUTOMATICALLY on starting up the Pi. Because of the way the HAT device works, it’s associated Python module runs inside a virtual environment. Getting ChatGPT to understand this nuance and to incorporate it into the code suggestions it was giving me took a long time!
WHAT NEXT This thing has taken up too much time as it is BUT I would like to
(1) laser cut some foam to create a neater housing / cavity for the box interior (inspired by Doug’s recent project!)
(2) nicer cable management inside the box (dream - I really want some kind of light cable retraction spring-power piece that is driven by the same devices used with retractable lanyards, so you can pull out the connectors and they will be lightly pulled back when un plugged)
(3) tweak the code to show multiple thermocouple readings (easy)
(4) put a dial-button on the front to use to adjust the X and Y axis scales, and reset the plot. (hard, potentially…)
Right now the X-axis is 120 seconds wide and the Y-axis runs from 20 deg C to 70 deg C, from values that are hard coded.
If I improve this thing meaningfully I’ll update y’all!