When I first brought my transistor clock kit, I wasn’t entirely sure how it’s timing circuit worked. Assuming it was some type of internal crystal oscillator, I soon discovered that it runs off of the 60Hz sine wave present on 110V AC power. This posed two important questions:
- Will it work in Australia, where we use 50Hz 220V power, and if not …
- How do I make it work?
The KABtronics manual shows the following diagram on page 25:
You can see the 60Hz signal coming from the wall, then dividing by 10 to get 6Hz, then dividing by 6 to get 1Hz. In the case of a 50Hz input, it’s divided by 10 (giving 5), then divided by 6 to incorrectly arrive at 0.83Hz. This means the clock effectively runs 17% too slow. Not great. If we modify the divide by 6 into a divide by 5, we’ll be all set:
Making the modifications
After cutting four traces and adding three links, the clock will work correctly, as described below.
On the front
1. Towards the bottom right of the board (where the prescaler is located), I cut two small traces, marked below with yellow dots:
Be careful with the cut between the diodes – there are two traces in there – you want the top most trace! Don’t cut them both. I could also have removed the diode (D52 to be precise) to the left of the yellow dot, but I didn’t want an empty space on my board.
On the back
2. I cut two more traces on the back, marked below with yellow dots:
3. Finally, I added three new traces to the back. The points you want to link are marked below with green dots:
The final circuit is shown below. Green lines are new traces, yellow dots are trace cuts.
After I made these changes, I fired up my clock and it was now timing correctly. You can see in the video below it’s not much more accurate compared to previously:
Tens of seconds are next. All the hard steps are now complete – I just need to power through soldering the 1,000+ remaining components and I’ll be done.