For the most part I was very happy with my Wanhao 3D printer. I performed all the usual upgrades of beefier MOSFETs, better cooling shroud, magnetic bed, Octoprint etc., but one thing always annoyed me; the constantly running cooling fan.
It was hard wired to turn on with the machine itself, and it’s not quiet. To some extent this is a classic first world problem – when the printer isn’t printing it’s switched off anyway, so it’s not really a big deal. On the other hand, when iterating a part there are times when there some minutes when I was making CAD adjustments before starting a new print and in this instance it wouldn’t make sense to power down only to switch it back on. Having the fan buzzing in my ear was quite irritating. I resolved to fix this in some way. What I came up with a simple (and classic) 555 timer based circuit that activated the fan when the filament heater was switched on, but kept the fan running for a couple of minutes after the heater went off. There were experiments and prototypes.
Honestly this had taken me quite a while, having needed to reawaken decades old analogue electronics knowledge. What I probably should have done is cut my losses and just use a microcontroller, doing it much more simply in software (simple is a matter of perspective here, I guess), but I’m stubborn and I persevered. To complete the old school look, I used a bit of stripboard, ending up with a daughter board for the print head’s connector block.
It ended up working pretty well, and hasn’t given me any trouble since.
Here’s the circuit.
