ESR Meter – What went wrong.

Posted by on November 6, 2010

Current PCB layout for the ESR Meter

Continuing with the ESR project, I’d like to enumerate the various issues I encountered during layout design, fabrication and finishing of the project.

I believe some people only show their “good side” and bury deep down each and every failure they suffered, however you don’t learn from winning and that’s why I thought it would be a good idea to write this.

These are some of the problems diagnosed during troubleshooting in no particular order:

  1. PCB Layout error, first revision circuit had a trace that was mistakenly connected to another component, this rendered the detector phase useless.
  2. Bad ceramic capacitor, the 470pF was damaged. Replaced with two 1nF in series to approximate the value.
  3. The transformer displayed losses at high frequencies, it was replaced with another transformer. (I still worry about the output level, it’s way under 100mV)
  4. Negative supply “biasing” potentiometer had one of the wires broken by the PCB end, most likely due to the amount of handling involved during the troubleshooting phase: always hotglue your wires!!
  5. Power supply wasn’t providing enough voltage for the opamp used, turns out 5v input is a no-go for TL082 due to manufacturing tolerances, etc. I had to go for 12V. The final unit uses 13.8V — I would like to go up to 15V but that calls for a different regulator.
  6. Deflection issues due to the 100uA meter, feedback gain was changed and a potentiometer was added for convenience.
  7. One of the test leads had a high resistance due to severed wires by the connector, this was a cheap DMM set of leads and I regret using them!
  8. The only TL082s I had were in SMD packages, so I had to etch a dip adapter board!
  9. My PCB layout was lost, well — the source file at least, this meant I had to redraw the entire layout from scratch, based on screenshots.
  10. Several placement and power issues during the last phase of the project were encountered, all of which have been fixed ever since — Although I’m not entirely happy with the placement of the potentiometers, they’re at a slight angle and this means their values will shift due to the slight pressure they’re under.

So, I wasn’t kidding when I said this wasn’t a simple project! — Probably the most problematic one thus far. However I didn’t give up and I could probably say I succeeded.

Special thanks to Lee and everyone in ##electronics @ freenode  for the invaluable help and support!

Have fun!

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