PCB agitator from a broken CD-ROM drive

pcb-agitator

Etching PCBs goes a lot better if you agitate the solution in order to carry away the dissolved copper and get fresh etchant to the area. With that in mind [Rohit Gupta] designed a mechanism in Sketch Up before realizing he was going about it the hard way. He ended up basing his agitator on a broken CD-ROM drive instead of starting from scratch.

He uses the CD sled from the drive, ditching the lens and its support structure. To get direct access to the motor that drives the tray he uses an L293D H-bridge chip. This is controlled by an MSP430G2231 microcontroller. The driver board seen in the upper right includes a voltage regulator, three status LEDs, and one user input switch. Once triggered, the sled will move back and forth, contacting an old mouse microswitch which acts as the limiting switch. We find it entertaining that [Rohit] prototyped the circuit on a breadboard, then used that success to etch the final circuit board (shown in the video below).

If you’ve been following the hacker creed and never getting rid of any junk you’ll have no problem finding a donor drive to make one of your own. But just in case you can’t get a hold of this hardware a similar agitator can be built using a hobby servo.

Comments

  1. Rodrigo says:

    Very interesting this solutions using old computer parts, i’m building a CNC from 2 cdroms and this will be my next project, both, to do PCBs

  2. Donovan Malloy says:

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  3. gaoip says:

    >Using an expensive microcontroller board where basic 7400 logic would do the job.
    Outsourcing anything but t-shirts to India never ends well.

    • indiantinker says:

      The controller is for free and so are other parts! Anybody with an address can get it from TI. I agree that it could have been implemented from logic ICs as well but i had the parts lying around.
      I although find the last line a bit derogatory!
      Thanks for the comment!

    • Sven says:

      We go over this every single time at hackaday, using a µC is often cheaper than logic in small volume, plus you can configure away any errors in software instead of going to get the iron again.

      Even in very large volume, using a µC can be cheaper than logic, a small controller isn’t that different from a logic chip in large volume pricing (millions of units) when mounting and everything is included.

    • No need for 7400 logic also. The tray mechanism has already a limit switch with two positions. A little modification to adjust the travel distance, two pull dow resistors, and feed directly the L293 intputs.

      • bodger says:

        logic free. many moons ago, in need of a qk fix i ripped apart a knackered scanner and with an old wormscrew lego motor and the largest cog hooked it up to a sledge that ran over the slide bars . a little bit of light oil for lube and an egg timer and done. the cam action only gave 10mm ish of linear motion but it was more than sufficient given it was such a shallow developer tray!

    • Anonymous says:

      You don’t really even need any logic at all, or the CD drive for that matter. Just an on/off switch and a motor with a stick attached with a pivot (like old locomotive wheels) attached to a sliding platform would shake back and forth enough. You could probably make something up with one of those under-mount drawer slides and a drill.

  4. Leithoa says:

    Cruised through the build log but didn’t see an explanation why he went with a switch to reverse motor direction vs just reversing after x (milli ?)seconds. Seems mechanically simpler. Maybe v1.1 could make use of a continually rotating motor and cam to slosh everything back and forth. No controller required.

    • indiantinker says:

      Hi,
      First of all its not a Stepper motor that handles the cradle its a simple DC Brushed motor. So if you change the voltage or load the time it takes to come back will change significantly. Hence a switch was required to detect the cradle`s position.
      Here is the final build video:

      Even the CAM arrangement is cool but i wanted to use old parts than to make an entirely new arrangement!

      Thanks!

      • Leithoa says:

        Thanks for the reply. I didn’t realize brushed motors were so imprecise. I figured you skipped the cam option since this was a recycling project as much as anything else. Keep up the good work.

    • Mr Name Required says:

      Yep, same thought here. A simple DC motor with a crank arrangement would have done the same thing, and completely foolproof to boot.

  5. dioxide says:

    hm. i was considering just attaching a vibration motor from an old phone or playstation controller either to the tank, or to the pcb clamp, to get that jewelry cleaning effect. as long as it doesnt do anything to the resist, it seems like itd be a very simple improvement over a standard tank setup.

    • Leithoa says:

      The jewelry cleaners are ultrasonic transducers. Unbalanced motors will certainly swirl liquids but it won’t give the same action of the sonicators you mentioned.

      • spyoxide says:

        indeed, and those transducers are available as well. i just suspected that reproducing the cleaning effect properly would strip the resist off fairly quick, and if agitation is the end result that im lookin for, a vibration motor seemed both quick and easy.

    • 0xfred says:

      I tried attaching the PCB to the end of an electric toothbrush – one of the cheap AA battery ones. I’m still getting started with etching and fiddling with a lot of different things, so couldn’t be sure if it made much of a difference. It was a handy board holder if nothing else.

  6. Brad says:

    Posted the comment on his site, but I’ll post it here as well. Great build. To minimize the wear on the end stop, could you have the tray first go to a home position (run it backwards till it hits the switch), move a predefined number of steps away from the switch, then begin the oscillation. The oscillation should now occur independent of the switch. Thanks for posting this. This is a hack in the truest sense.

  7. pff says:

    “he realised he was going about it the hard way”
    the hard way like using a micro controller to reverse a motor when it hits a switch?

  8. RicoElectrico says:

    I don’t get it why people would use ferric chloride for etching PCBs anymore? Don’t you folks in the USA, India and other countries know about sodium persulfate? It minimizes over-etch, is safer, doesn’t stain everything (although it bleaches textiles), its solution is clear so you can see the copper being etched away.

  9. kristian says:

    I’m curious… wouldn’t shaking the solution worsen over-etching? It seems like more etchant would make it underneath the photoresist if it’s flowing transversely.

    • Sven says:

      It seems to me that the longer the board stays in the solution the more etchant creeps under the resist, if you etch fast there is very little creepage under the resist.

      Commercial etching machines use moderate to high pressure sprayers with etchant and etch boards in as little as 30s.

      • pcf11 says:

        Air entrancing (air pumping) you can get an etch in 2 minutes. So far that is my personal best using FeCl. High pressure spraying corrosive materials isn’t for the faint of heart either. So I’ll settle for the extra minute and a half I’m taking over what the pros are doing.

  10. pcf11 says:

    Use air. Once you’ve used air in a tank you never go back to shaking. Get one of those cheap ass 12V tire inflation air compressors and stuff an aerosol spray cap on the end of its hose, into the tank, and you’re golden. Anything else is total Tomfoolery. Oh, and heat your tank until it just starts to fume, around 110F. You’ll enjoy etches in under 5 minutes with air, and a heated tank.

    • Or an aquarium pump and a air stone like people used to use.

      Or send the boards out to OSHPark (My favorite)

      • Sven says:

        Or just go buy an Arduino and the appropriate shield!

        Or what the hell, everything has pretty much been made already, just buy the finished product from somewhere.

        (i felt a distinct lack of Arduino in this post so i had to mention it)

      • KleenexCommando says:

        Exactly… This is engineering overkill. Take a simple little task and turn it into something way more complex than it needs to be and then wonder why it never quite works right… Air stone, aquarium air pump and some tubing… Simple. Just make sure to keep the pump above the level of the etching solution – a shoe box or something will work, no need to build a freaking suspension bridge or anything to hang the pump from.

      • pcf11 says:

        I’ve heard the aquarium pumps work well too. But I’ve never kept fish, so I never had one just kicking around to use. My point is pumping air into an etch tank is the best way for a hobbyist to enhance their etching setup. Sure pressure spraying is the very best method known to man but I submit that is not worth getting involved with due to the range of complications it presents. Pumping air into an etch tank is about as easy as dumping a hose in, and going. The results speak for themselves too.

        I’ve personally etched boards in 2 minutes air pumping, and using a heated etch tank. Boards that I might add came out perfect. No undercutting, and no under etched sections. What else are people looking for?

  11. Mark says:

    I’ve done the same with one 555, one BJT and nothing else…

  12. micaF says:

    For what is’s worth. The earliest one I’ve seen.

    http://www.instructables.com/id/PCB-agitator-from-an-old-CR-ROM/

  13. Carlos says:

    LOL… I made mine years ago just using one old drive with micro switch (just changed a bit original micro switch of drive), a pair of relays (one DPDT can do the trick), linear regulator and a power supply…

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