Theremin w/Zapper,laser,Arduino using arduino

I created this Theremin like device after seeing this article in Make magazine:

While this looked pretty straight forward it turned out to be a bit much for me at the time.  But after much effort, I got it to work pretty good.

I had trouble getting the laser to aim correctly so I chose to mod a zapper I had available to hold the laser.  This worked well.

So I will recap the steps:

Step 1: Video of finished and working

I found software for the Mac that is fun to play with. SimpleSynth has many different instruments or events that the midi stream emulates.
Here I am randomly choosing different styles .

Step 2: Get stuff

Parts that are needed:

Basically I used the parts list that is on the first page of the Make Magazine article.  But that list is for the harp which has 6 lasers so most quantites can be just 1..

1. Arduino – I used a Diecimila
2. Inexpensive laser pointer – I got a red one from eBay for a couple of dollars
I was hoping to be able to see the laser but have learned that red will not show up unless it is quite powerful.
So it might be better to have a green laser instead of red.

3. Power Source – I used an AC adapter that I had . It outputs 12Volts and 1.7 Amps.
4. Adjustable voltage regulator – used the Trossen #P-VR-DE-SWADJ
5. 5V – 7805 voltage Regulator – I got from Jameco –  pn 51262
6. LM324 quad op-amp chip – Jameco – 23683
7. Red LED – I had – can get from Radio Shack
9. Resistors – 220 ohm
– 1.5K
– 3.9k
–  68 K
– 1M

10. Photocell – 100mw – jameco – 202403
11. IR range sensor – Trossen – GP2D12
12. tumbled rock – Hobby Lobby
13. potentiometer – 100k – jameco – pn29103
14. 5 pin DIN MIDI connector  – jameco   pn 15844
15. circuit boards – radio shack

Also a midi cable to connect the Theremin to a MIDI device eg a computer running software that can interpret MIDI input.   I got one from eBay for about 10.00.

Step 3: Schematics

The Make article refers you to this link   .  You can then download a zip file with schematics.  I have photoed them and attached here.

As I am new to this I had to do a lot of head scratching and trial and error to get things working .  But I believe i learned a lot.

Step 4: Building it – Power Supply

I did bread board this but I did not take pictures at that time .

To make it simpler for me to understand, I separated the major parts onto separate circuit boards.

It seemed to make it easier to follow the flow of the schematics, at least for me.

The Power Supply:

8.5V goes directly to the Arduino to power the Arduino.
8.5 V goes directly to the Trossen adjustable voltage regulator.  After the rest of the wiring is done, you adjust the regulator to output just enough voltage to turn the laser on.
8.5V goes to the LM7805 which outputs 5v to go to the Sharp sensor.


Step 5: Build it – Detector circuits

The article has a good description of how this is done.

5V from the 7805 goes to the LDR.
The output from the LDR becomes input to the LM324.
When the beam is broken, no voltage will go to the LM324.
The output from the LM324 goes to digital pin 2 on the arduino.
The potentiometer is used adjust the voltage to the LDR.  Adjust to the point where the LED just comes on.
Of course , refer to the schematic for the complete circuit.

A data sheet for the LM324 can be found here;

Step 6: Build it – Midi Jack

Follow the article instructions:

Green to TX pin on Arduino
Black to ground
Red from 5v – thru a 220 ohm resistor


For more detail: Theremin w/Zapper,laser,Arduino

This Post / Project can also be found using search terms:

  • lm324 テルミン
  • lm324 arduino
  • zapper with laser therapy circuit

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