Take a Picture

Learned another lesson today: take a picture.

I've been a photographer since grade school but possibly that hasn't always served me well in the 21st century.   Nowadays once the camera has been purchased each picture taken is essentially free.  In the olden days it cost money to buy film, develop and print it - and I did my own B&W developing.  In addition, it was a certain time sink to process the film.  So maybe I'm unconsciously avoiding picture taking ?

Today I was working on this:

It's the clock module from the old Westclox clock that has been on/off the shame shelf seemingly since the battery leak.

https://wb9kzy.blogspot.com/2023/05/boss.html  

I had ripped out the battery contacts (all corroded) and soldered wires to an external battery holder.  But something just wasn't right.  Sometimes it works, sometimes not - bad for a clock.  It's a shame because the module kept excellent time.

Today I was going to touch up the soldering, just in case old battery corrosion had messed up the joints.  The first wire came off the pad so I proceeded to the second pad and promptly the wire came off that one, too.  Then I got interrupted by the mail and when I returned I realized that I didn't know which pad was which !  At first I tried using the ohmmeter - it was infinite ohms in one direction and several megohms in the other direction - but I wasn't sure what that meant.  Was I just in-effect measuring a reversed biased diode across the leads or ?

Then I realized that I had taken a picture with the leads still connected  - I got out the camera and bingo, I knew the correct polarity.

also, the + symbol is a hint isn't it ?  :)

My memory has always been lousy so I can't chalk forgetting which wire went where to old age.  But from now on I'll be taking more pictures when fooling with projects !

BTW, the module looks pretty simple, it drives the motor with pulses once a second.  However in my experience this relies on either MOSFETs optimized for 1.5 volt operation OR they use bipolar transistors because it is hard to turn on a MOSFET fully with only 1.5 volts on the gate.  I tried subbing my own electronics on an analog clock and it just wasn't reliable enough, the clock would lose time because the second hand wasn't always being actuated - it wasn't due to the crystal frequency being off.  So either it was the pulse timing or the transistors weren't reliably actuating the motor.

However I didn't have a digital scope then so wasn't able to capture the timing that easily - maybe I should revisit the topic ?

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm