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:
- PCB Layout error, first revision circuit had a trace that was mistakenly connected to another component, this rendered the detector phase useless.
- Bad ceramic capacitor, the 470pF was damaged. Replaced with two 1nF in series to approximate the value.
- 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)
- 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!!
- 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.
- Deflection issues due to the 100uA meter, feedback gain was changed and a potentiometer was added for convenience.
- 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!
- The only TL082s I had were in SMD packages, so I had to etch a dip adapter board!
- 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.
- 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!