Cheap And Easy PCB Agitator From An Old CD-ROM


Instructables user [mzsolt] enjoyed making his own PCBs, but he wanted to speed up the etching process just a bit. While some people put together elaborate bubble tanks and agitators, he wanted to keep his simple and more importantly, cheap.

He looked around the house and discovered an ancient CD-ROM drive that was collecting dust, which he figured would make a great agitator for smaller projects. He picked up a decade counter and a handful of other cheap components, then got busy pulling the drive apart. He connected the motor and the drive’s limit switches to the decade counter, which controls the entire setup.

When powered on, the drive ejects, taking his container full of etchant with it. When the drive hits the outer limit switch, the decade counter reverses the motor until it hits the inner switch, reversing the motor once again.

As you can see in the video below, it works reasonably well. He suggests using a variable power supply to regulate the motor’s speed, but a variable pot would probably work just as well. Obviously the agitator is best suited for smaller projects, but since it was so cheap to put together, you won’t hear us complaining.


32 thoughts on “Cheap And Easy PCB Agitator From An Old CD-ROM

  1. Clever idea! but like @spiderwebby says, it’s annoying to stay near it.
    I also think you probably won’t get that much life out of it considering the mechanical stress and that the gears are plastic…

  2. When I seen the title, and the photo I really did LOL, from the instant imagination of it in operation. Original AFAIK. Personally I think it too noisy, but your sure not to forget to check the progress of the etching, so you can finally turn it off.

  3. I think the inner limit switch should be adjusted outwards so that the tray is not allowed to “dock”. Theres a gradual deceleration happening that doesnt shake the tank as much as the sudden change in direction does at the other end.

  4. I dont think it needs that much linear motion. I can hear the gear assembly that raises/lowers the laser platform. I would have removed it or move the stop switch at the end of the tray to minimize the noise, No need to raise/lower something that doesnt exist. Also keeping the gear assembly lubed will keep noise to a minimum. But the build could be worse the whole assembly could have been belt driven like many of todays drives, It would have failed in a day.

  5. It is possible to do this with an unmodified drive (at least electronically).
    Simply make it impossible for the drive to open all the way and make it so when the drive closes the eject button is depressed.

    Great idea!

  6. I use a glass tank 2cm wide 30cm long and 20cm high. It has a long aquarium air stone in the bottom fed by a cheap aquarium air pump. Have to replace the air stone about once a year. Works a treat.

  7. I built my stirrer out of of my old k’nex. I use a small motor mounted to legs which hold it over the tub and a stir thing goes down into the mix. Its completely silent and the etchant obviously wont eat plastic k’nex. Still playing with my toys!

  8. Love it. Maybe it’s not the most silent solution for this problem, but very practical one, as almost every tech-savvy person has some not-exactly-working cdrom around

  9. ^ I LoL’d. But I completely agree. I’d go nuckin’ futs.

    I had a completely different preconception of what it was going to do before watching the video of it in action. I thought it was going to power the disc-spinning motor and then use vibrations from that to agitate the solution. But now that I have that idea, I think I might run with it, possibly attaching a bar magnet and then plopping a piece of vinyl-coated steel bar into the tank. It doesn’t take much to keep the solution circulating and effective, does it? Though it depends upon the geometry of your PCB & tank, and the amount of solution you use.

    Take that, multi-hundred-dollar laboratory equipment makers!

  10. @ bobdole

    $ while true; do eject /dev/cdrom ; sleep 1 ; eject -t /dev/cdrom; sleep 1; done #and let’s hope your cdrom is supported!

    @original poster

    Very cool hack, but fumes from the PCB etchent will attack the metal in the CD-ROM drive. This is actually a very good reason why not to etch PCBs near your computer or in your kitchen.

    Also, the bubbles from a aquarium stone somehow do a far better job on etching than mere agitation or a circulating pump will produce. I’m not sure why though.

  11. @sneakypoo i also do this, however dont the fumes get to you? i find myself unable to be around the mixture for longer then 30 sec’s without feeling like i’ve been nova gased lol

  12. Maybe scale it up a bit? Several drives moving simultaneously attach short legs to the drives so that you can move a much larger tray.
    Although technically it only has to be as wide as the pcb. Why not two paines of glass five mills or so apart drop the pcb in with hooks so you can retrieve it easier. A line of air hose with holes (or several small air stones at the bottom). You would use less etchant and check the progress more easily.
    Maybe a pipe on the bottom with a small plastic tap to empty etchant. (think I saved some of thoughs little ball valve taps from a wine box a few years back). Lifted in and out of a rack with a robotic arm CNC style I could just leave it etching 20 boards a night :D

  13. Can be done even without extra electronics, most disk drives notice they’re “stuck” so jamming them at both ends keeps them going :).

    (although this has more potential)

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