The subject of this analysis is the $2 Ikea Stomma wall clock. Unlike the Rusch wall clock that had been the object of my experimentation all along, this clock uses a sweeping clock mechanism, which means the second hand appears to move continuously instead of every second. This also means it is quieter and does not produce the familiar tick-tock sound.
Note: Both clocks appear to have been discontinued at the time of writing. There is only one $2 clock on sale at their website now, which is the Tromma clock. I don't particularly like this clock, because the second hand is missing, which makes it difficult to tell if the clock is working at any instant.
The hacking process of the Stomma clock is quite similar to that of the Rusch clock, so no suprises there.
I inserted a AA battery into the clock mechanism and hooked up the wires that were just installed to a logic analyzer to check out the signal produced.
- In my test, the power draw is about 10x when driving the sweeping clock mechanism.
- The pulse width cannot be lower than 32ms if the clock is to be driven reliably.
- However, the rest time between pulses can be as low as 8ms (versus the current 62.5ms - 32ms = 30.5ms). This means the maximum rate at which I can fastforward the clock is about 150% (62.5ms / 40ms). In contrast, the maximum rate for a non-sweeping clock mechanism is about a whooping 800% (1sec / 120ms).
- The stay-in-place ticking trick (by pulsing the same tickpin repeatedly) does not work with the sweeping mechanism.