## Introduction: DIY Turntable and PCB Etching Shaker Circuit

In my journey as an electronics circuit designer and a Youtuber on the same topic (My Channel: https://www.youtube.com/channel/UCWG0DXu5ineRh85VH...), I always wanted of these two things:

1. A rotary turntable to show off my circuits for my YouTube videos.
2. A Printed Circuit Board(PCB) shaker so that I can shake the etchant (etching chemical solution) to automatically to etch off Ferric Chloride for making homemade PCBs. I'm tired of shaking off the etchant by hand, phew!!.

Now at the beginning I was thinking of two separate circuits for the two cases but then I thought why not to make a single circuit which can serve both the purposes for me. Now I was determined not to use any microcontroller for the job, since I always consider them to be an overkill for these simple tasks. So that's why I came up with a circuit using our very own and favorite 555 Timer IC. Now to drive the DC motor, a L293 motor driver IC would be enough. With some simple resistors, capacitors, diodes & switches, the circuit can be made easily, and also you can learn more of basic electronics on the way, rather than just writing a code in microcontroller.

Features of the Circuit:

1. Two modes of operation, turntable mode and shaking mode, any one to be used at a time.
2. Manual speed control for both modes.
3. For turntable mode, clockwise and anticlockwise modes are there, any one to be used at a time.
4. For shaking mode, the to and fro motion time can be controlled manually

In the following steps, we will learn the circuit from schematic to implemenation.

## Step 1: Parts Required

1. 556 IC (Dual version of 555)
2. L293D IC
3. L7805 IC
4. 5 4.7k resistor 0.25w (not critical value, anything between 1k -10k is enough)
5. 1 330ohm resistor 0.25w
6. 2 1k resistor 0.25w
7. 1 470ohm resistor 0.25w (not critical value, anything between 470-10k is enough)
8. 4 1N4148 diodes
9. 1uF capacitor
10. 220uF capacitor
11. 1000uF capacitor
12. 100uF capacitor
13. 10k potentionmeter
14. 10k dual gang potentiometer
15. 1 slide spdt switch
16. 1 slide dpdt switch
17. 2 BC548 npn bjt (or anything similar types)
19. 1 LED
20. Soldering iron, wires, breadboard, PCB or veroboard
21. 12V DC Motor
22. Mechanical parts for making the platform and supporting structure (can be wood, metal, etc)

## Step 2: Circuit Explanation

The circuit is attached in the PDF attached here in this step. Follow the circuit along with the datasheets.

Shaker part: The 556 has 2 independent 555 timers, one used for PWM control (speed control of the motor), the other one used for setting to and fro timefor the motor.

The U1A of NE556 in the schematic is for the PWM control. It uses the popular pwm control circuit with 555 timer. It has 2 1n4148 diodes along with the potentiometer, varying the potentiometer causes to change the duty cycle by changing the charging and discharging times of the capacitor. Standard PWM frequency can be used as 50-100Hz. The calculation for the same is also attached in the picture attached in this step.

The U1B of NE556 in the schematic is for changing the to and fro times. The 2 diodes here provide the fixed 50% duty cycle, which is essential since to and fro times must be equal and uniform for efficient shaking of the etchant. So by varying the two resistors (essentially dual ganged potentiometer), we can change that time. Do note that whatever be the on-off times, duty cycle is always maintained as 50%. The total time period can be as long as 3 sec. You may change R C values to get different time periods. The calculation for the same is also attached in the picture attached in this step.

The motor driver used is L293D. Only one channel is used. The PWM output from U1A is fed into the EN (Enable) Pin of a channel. Now to feed the 2 control signals, we need an inverter to get complementary signals. So the output from U1B is inverted using a npn BJT configured at the saturation region in common emitter mode of operation. Therefore we get the two control signals. It does not matter which signal you're feeding into which control pin of L293D, as long as the two signals are complement of each other it will work just fine.

Turntable Part: Now turntable mode is a simple mode of operation where the motor will run continuously in one direction. For that the control signals must be fed accordingly. For example, if inputs 1A & 2A are given as 1 & 0 and motor is running clockwise, then by setting 1A & 2A as 0 & 1, motor will run anticlockwise. To change the direction (clockwise or anticlockwise), I have used another BJT as an inverter and a simple SPDT(single pole double throw) switch can help us to set the inputs to the L293D as shown in the schematic.

A simple DPDT (double pole double throw) switch can be used to switch between two modes. This switch will just simply switch the control inputs to the L293D, either to be set to turntable mode or shaker mode, as shown in the schematic.

Now the motor I have used is a 12v DC motor whose minimum operating voltage is 9v, it cannot run on 5v. But the L293D Vcc1, EN and the control inputs supports 5v logic. So that's why a L7805 regulator is used, so that it can supply 5v to the 556 to get 5v logics which is compatible to the L293D as well as feeding the Vcc1 of L293D to 5v.

Supply capacitors are very much important. For 12v rail, 1000uF is necessarily be used (or higher) to deliver ample surge current for the motor. For 5v rail, a 100uF and a 100nF are sufficient,

A red LED is used as a power indicator.

### Attachments

I have built the circuit on breadboard and tested it. It works perfectly fine. You may observe the video files attached here. I have also used my DSO to test the various PWM and control signals. Do note that we have taken ideal conditions, so we considered diode voltage drop as 0. But in reality 0.6v drop is generated at diodes, thus the actual PWM frequencies and on-off times are slightly different with the theoretical calculations. But that doesn't pose any serious problem and circuit works flawlessly. I can easily switch between two modes and can also change motor speed. I used 8.5v Vcc from two 18650 batteries connected in series. The DC motor used is a 12v 60 RPM motor.

For building the platform and supporting structure, I have used mechanics lego toy parts. You may use wood or anything else, whatever comes inside your creative mind.

## Step 4: PCB Making

I have used Kicad software to make the schematic and PCB. Then I used toner transfer method using cloth iron. And the very first PCB which I made with this shaker circuit is this circuit board itself. For this, I have used the breadboard circuit to etch the PCB, then dismantled the components from breadboard, drilled holes and soldered onto PCB. Attached switches and hookup wires. Then again I tested with the finally made PCB. The PCB file is attached here.

It was a big success as I achieved both of my purpose using this single circuit that too without any microcontroller.