L/C meter kit

This post is LONG overdue since I didn’t get around taking the pictures. I wrote it on August 22.

A few weeks ago (= early July -ZO) I engaged in a two way e-mail discussion about the details of a circuit with the guy who engineered it. Suddenly he asked: “You do have an L/C meter, right?”. Errr, no? Actually he had a point: it’s hard to get something working without measuring the actual values of coils and self-made caps. I was counting on luck which is of course the worst an engineer can do. You might be lucky and the circuit may work but most circuits don’t and how could I even troubleshoot whatever thing I have on the bench without an L/C meter?

In my defense I must say that I never had to wind coils where the value is critical – if any. And I hate winding coils. Traumatizing experience winding a high N coil for an oscillator in school. Twice! Don’t ask.

So I started looking for an L/C meter. Semi-professional lab models were expensive. No way I would spend a few hundred Euro on that! One vendor even tried to mate me up with an Agilent LCR meter. Hello? There were many DYI designs in the Google results. But I have no tools to program microcontrollers and don’t feel like messing around with perfboard again. But there were kits on sale with programmed CPU’s and silk screened PCB’s. So I settled for the Electronics-DYI.com LC meter kit. It has a nice blue display (love blue!) and it came with a free enclosure.

It took only a few days for the kit to arrive. Thank you mailwoman! No hassle with Belgian customs. They must be on holidays. Seriously: small parcels and envelopes usually get here wihout a problem. Soldering the kit means nothing and instructions are very clear. I hooked the completed PCB up to the power supply and tried some caps. Success. It worked. The only adjustment was turning the LCD contrast potmeter for optimal visibilitiy. Now to get it into the enclosure.

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Disclaimer: my micro-mechanical skills are poor (apart from soldering small parts). I can drill M10 holes through 10mm thick plates. Digging holes in the ground? Not a problem. But the size of the plastic enclosure relative to the PCB + display is on the small size. So I label it ‘micro mechanics’. Not much room left if any. Electronics-DYI.com supplied a richly illustrated two page step by step manual on how to prepare the little plastic box. There were some standoffs in the way that needed to be removed. They suggest melting it away with the soldering iron. I must admit I am familiar with this dirty but fiendishly technique. However it seemed too much plastic in a critical place to melt away. The hot plastic might deform the backside of the case.

Finally I would be able to use my Dremel multi-purpose drilling-grinding-milling tool! Finally since I bought it in 1998 when I graduated and started making PCB’s at home. An activity I soon gave up on. The Dremel didn’t get to dremel until now!* I put up a small thin disk, cranked up the RPM and attacked the plastic parts that needed to go away. Due to the heat generated by the friction the plastic melted anyway. I was able to grind away the blob and smoothen the surface with another accessory but needed to pay attention not to slip through from inside to outside, ruining the case’s view and finish.

So far so good. Now I needed to cut away the rectangle in the lid (LID HI) where the LCD should come. The plan was to use the small high RPM grinding disk. But again the plastic melted which made the cover look all wobbly so after a few centimeters I quit using the dremel and just went over the outline with a heavy cutter knife. After a few times from both sides I was able to squeeze out the window for the display.

A few more holes were drilled for the wires (power, L/C) and buttons (L/C selection and calibration). I printed a paper with ‘ON5ZO L/C meter’ on it, laminated this, cut it to the right size and shape and used double sided adhesive tape to stick it on the cover. There you go: my L/C meter.

* I realize I was wrong about the Dremel. I actually used it about one year ago. Someone asked me to look at a malfunctioning audio amp. Obviously I wasn’t his first choice since a miserable attempt had already been made to open the amplifier. This guy (gal?) had worn out some of the Philips head screws. I tried to open it but made the problem even worse. Which was to be expected: worn out heads are a pain. So I took the Dremel and mounted a small grinding disk to carve a big slot into the screw’s head so I could turn them with a slotted screwdriver. I didn’t even take a shot at the amp: almost every component in the left channel had blown, from bias resistors of the driving stage to final stage transistors and literally everything in between. Including burned copper and skidmarks of missing traces on the PCB. On a cheap ‘no brand’ amp without schematics? Get outta here!