Skip to main content

Running an analog clock backwards

I didn't think it was possible, but recently I came across this YouTube video and its associated blog post (in Japanese, which I was able to understand thanks to Google Translate):

Here's a diagram to contrast the pulses sent to the clock lines to turn the clock backwards, versus driving it forward:


As you can see, during the first time step, instead of sending a single positive or negative pulse, you send a short pulse, wait a little, then send a longer pulse in the opposite direction. Then in the next time step, a mirror image of the pulses in the previous time step is sent. The duration of the pulses has to be experimentally determined for different clock motions.

For example, I was able to use this follow code to move the second hand on my clock in a reverse motion reliably:

int tickpin = 25;

void rtick() {
  digitalWrite(tickpin, HIGH); delay(10);
  digitalWrite(tickpin, LOW); delay(10);
  tickpin = (tickpin == 25 ? 27 : 25);
  digitalWrite(tickpin, HIGH); delay(30);
  digitalWrite(tickpin, LOW);
} 

So the short pulse is 10ms, the short wait is also 10ms. The longer pulse is 30ms.

Here is a video of the clock in reverse motion:


I was able to reverse-drive the clock reliably up to 4x speed using the code above. I pause the second hand after every 60 ticks, and noted where the stoppage point is. Then I let the code run overnight and came back in the morning to check that the second hand is still stopping at the same place.

But once I tried increasing the speed to 5x or 8x, slippages started to occur.

Comments

Popular posts from this blog

Update: Line adapter for Ozito Blade Trimmer

Update (Dec 2021): If you access to a 3D printer, I would now recommend this solution , which makes it super easy to replace the trimmer line. I have been using it for a few months now with zero issue.

Line adapter for Ozito Blade Trimmer

This is an adapter for Ozito 18V battery trimmer (and possibly some Bosch trimmers as well) that uses a plastic blade for cutting. It lets you insert a 2.4mm trimmer line (about 8cm long) and use that for cutting. Simply cut a length of trimmer line and briefly heat up one end with a lighter so that a little bulb is formed. Then insert the trimmer line into the adapter and slot that into the trimmer as per normal. Make sure the trimmer line is not so long that it touches the safety guard. If that is the case, simply trim off any excess with a cutter or scissors. This part is best printed using PETG, which is a tougher and more flexible material. PLA is more rigid and breaks more easily. However, even with PETG, it will still break when it hits something really hard. Since this takes only 0.5m of material and 15 minutes to print, I will usually print a batch of nine at a time at very little cost. The blades that they sell do not break when it hits a hard object, but ...

3D Printer Filament Joiner

I have been looking at various ways of joining 3D printing filaments. One method involves running one end of a filament through a short PTFE tubing, melting it with a lighter or candle, retracting it back into the tubing and immediately plunging the filament to be fused into the tubing: One problem with this method is that you can't really control the temperature at which you melt the filament, so you frequently end up with a brittle joint that breaks upon the slightest bend. Aliexpress even sells a contraption that works along the same line. As it uses a lighter or candle as well, it suffers from the same weakness. I am not even sure why you need a special contraption when a short PTFE tubing will work just as well. Another method involves using shrink tubing/aluminium foil, and a heat gun: But a heat gun is rather expensive, so I wanted to explore other alternatives. The candle + PTFE tubing method actually works quite well when you happen to melt it at the rig...