Another Chemical Agitator




Introduction: Another Chemical Agitator

About: These instructables are mostly about electronics. I hope you find them helpful!

Hi Instructables,

Over the past years I have been making PCBs by just watching it etch away. Sometimes I would heat up the chemicals in the microwave, jiggle it around manually, use a stirrer, or a straw to facilitate the etching process.
You all probably know that by agitating the etchant, it etches faster. I don't throw out etchant that often (in fact I have never), so my it gets old, colorful, and ineffective.

Since I do not want to manually agitate, I decided to have an automatic agitator. There are many designs out there already.

Microcontroller and H-bridge:
Arduino and H-bridge:
555, 4017, 4 transistor H-bridge:

I wanted to build one of these, but I did NOT want to use $30 hardware (Arduino) to do a simple back and forth motion, and I did NOT want to deal with the crazily pinned 4017 decade counter.

Look at the pinout of LM4017. It's crazy and not easy to play with.

Anyways, I decided to design a cheaper circuit with the same functionality.
Before I continue, I would like to give a special thanks to the people on the Arduino Forum for helping me debug the circuit.
I would not have accomplished this without them: michiyon, TomGeorge, JohnLincoln, MarkT, MAS3, polymorph, and cjdelphi

Step 1: Parts, Dissassembly

Here is a parts list:
  • 100 uf capacitor
  • 2*1k resistor
  • 10k resistor
  • 2*5v relay
  • 9v battery and clip
  • 2n2222 transistor or the like
  • CD drive
  • 4007 power diode (or the like)
There are also some parts I left out that you might want to add: 0.1 uf capacitor for power supply, for example
refer to the schematic. Remember that this schematic is not absolutely solid: you could change it around a bit for better functioning. I simply put up the schematic I used for simplicity.

If you have any questions, you can comment them below :D

After you have gathered your parts, you should disassemble your CD drive.

Sorry that I do not have pictures of this, as I disassembled my CD drive years ago and forgot all about it.
Once you disassemble it, find the motor that opens and closes the CD drive. You can test this by applying 5v to random motors on the drive. Do not worry about polarity or burning out your motors. It should be fine :P

Step 2: Building the 555 Circuit, and Explanation

I took a rat's nest approach to this circuit. it was smaller that way

You might want to use a perf board or a PCB.
Whatever the case, as long as it works it works; the schematic should be pretty straightforward, but I will explain it here:

The 555 timer sends a pulse HIGH and LOW, timed by the 100 uf capacitor.
Think of it as the BLINK example on Arduino.

This pulse of HIGH and LOW is send to the transistor, which switches CLOSE (HIGH) or OPEN (LOW) depending on the state of the 555 timer.

The transistor acts as a switch to complete the relay circuit to make the relay turn ON or OFF.

When the relays are ON, current flows one direction, making the motor turn that direction
When the relays are OFF, current flows in the opposite direction, making the motor turn in an opposite direction.

I am using two SPDT (single pole dual throw) relays to act as a DPDT (dual pole dual throw) relay to be an H-bridge.
I did not want to buy an expensive semiconductor H-bridge,
and I did not want to make a 4 transistor H-bridge (there is much current loss).
So, I used relays.

Step 3: Connect the 555 Circuit

Connecting the 555 circuit output to the CD rom is more of a guess-and-check process.

Connect the motors to the output in any polarity

Does the CD drive come out? If you hear a whirring sound and the CD drive is not ejecting, just switch the wire connection.

The CD drive should come out once you start up the circuit.

Step 4: Thanks

Thank you for reading this instructables!

Remember, original documentation is here:

If you have any questions or suggestions comment them below.

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    Helen GGG
    Helen GGG

    8 years ago on Introduction

    I have seen with pleasure the instructable, but! I find it very complicated and just now I saw one like youtube but simpler to construct