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PCB v0.1 design and errata

A project log for Simple Thermal Camera

A thermal camera using a 32 * 24 pixel sensor. Designed to allow lots of substitutions due to the parts shortage!

nrwestnrwest 09/12/2021 at 04:350 Comments

Before I send a new PCB design for fabrication, it's good to double check a few items:

Back when PCBs cost over $10 per square centimetre, it was important to minimise their size. Now that they are cheaper, I think improving usability of the PCB is usually a good trade off. Of course there will be exceptions!

During the present chip shortage, it's often a good idea to provide accommodation for component substitutions, if possible. This might include:

So, when I got the shiny v0.1 PCBs from the factory, I noticed that I had made one mistake and somehow swapped the SCK and MOSI lines for the screen on the schematic! Stupid. I had to mend this on the v0.1 PCB by manually soldering wires at R6 and R7. After a bit of testing, I also noticed that the readout for battery voltage is quite noisy. My oscilloscope shows ~230mV of ripple at ~150Hz on the input side of the DC-DC converter. The noise seems similar regardless of whether the unit is running from batteries or a lab power supply. Regardless of the cause, a capacitor between the ADC pin and ground helps smooth out some of this noise.  To fix the v0.1 board I added a 1µF SMD capacitor (the first value I had at hand) in parallel with R9. Before I added the capacitor, ADC readings would fluctuate by ~50, the capacitor reduced them to ~3. It’s probably better to use a couple of caps of different values to remove different frequencies of ripple, but the 1µF is definitely "good enough."

There may be other mistakes that become apparent as I do more testing. There will definitely be features I want to add, and the community might have suggestions too! at some point I would like to do a second revision of the PCB, but at this stage I don't have enough information to commit to a v0.2. The v0.1 is more than sufficient for testing.

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