TomWhen opening the housing,
there are some eye-catchers:
- The part numbers of the instrumentation amplifiers and of the differential amplifiers are burnished away.
- The white wire which connects the negative supply of the differential amplifiers.
- There is no galvanic insulation between the USB port and the measurement circuit.
The PCB is assembled single sided, probably it is a 4 layer stack-up.
Using a microscope i was able to read the part numbers of the burnished components. You find a list of the key components in the components list!
The clock output of the device is connected directly to the CPLD pin using a 33 ohm resistor.
From the hardware perspective this devices looks well designed with little discomforts:
- The 4mm banana connectors do have a very bad quality
- There is no galvanic insulation between the measurement circuit and USB
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Nice! First thing I looked for was galvanic insulation and thought that maybe U21 was there for that purpose. Then read through it all.
- I think the bad banana plugs are not a "little discomfort". The connection to the outer world should be as reliable as possible with as little resistance as possible... Why cheap out on those parts?! This unit is 600USD!
- Scraping the top of your ICs is just bad. But fortunately they did it like they did their banana jacks :)
- The Kelvin connection of the current sense resistor looks far from how you do it "by the book". Especially those super long traces to the ADC/CSA. Routing would've been possible on the right side too?!
Edit: Please add the designator from the parts on the board when filling your component list. It's much easier for us to see where each part is on the board!
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Hi Jan :)
U21 is a TVS diode.
Several things are solved the cheap way and not the more expensive but elegant way.
You can always do things better ... ;)
I added the designators to the component list.
I just calculated the costs of the key components with about 35€ (30pcs batch).
Are you sure? yes | no