A Raspberry Pi controlled mini CNC Laser engraver [last update Jan 18,2014]

Due to the size limit of DVD drives, the machine can only engrave within an area of 36 mm by 36 mm.. So it can do little pieces of wood, plastic board or part of  iPhone cases, but not any larger.

The laser used here is 200 mW 650 mm red laser diode. It cuts letter paper fine. But It is not powerful enough to actually cut through anything thicker and tougher. In fact, the working surface is preferred to be black color so that it can absorb as much laser power as possible. To engrave on transparent plastic board, as shown above in the coin size university icon picture, I have to use a black marker to paint the surface and clean the ink after engraving. However, I believe for a thin black foam sheet (<3mm thick), and given enough engraving time, the laser should be able to cut it through, as Groover showed in instructable.

Now here is the instruction.

Things required:

1. A raspberry pi (running Raspbian or what ever supports GPIO)

2. two DVD writable drives.
To be able to engrave, you need 200mW laser diode from DVD writer. A DVD R or CD R will do nothing. A CD writer might be OK in term of power (~100mW), but the laser diode of a CD writer is infrared, which can be super dangerous (you can’t see it!).3. a TO-18 5.6mm laser housing
(like this one http://www.ebay.com/itm/251316903193?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)
Make sure you get a 5.6mm one. There is another type 9mm.

4. Two dual channel H-bridges.A H bridge is a circuit containing four (effective) switches that can apply a voltage across a load (DC motor or one coil of a stepper motor) in either direction.

Stepper motors from DVDs are 4 wire 2 phase bipolar stepper motors. They require truly reversible voltage on each pairs of the wire. You need two H bridges for each stepper motors. So total of four H bridges for two strepper motors. Some famous stepper motor controllers like ULN2003 are for the 5 wire stepper motors, so they cannot be used for controlling the DVD stepper motors.

You can make your own H bridges by using 4 NPN and 4 PNP transistors and probably TTL converters (RPi’s GPIO pin are 3.3V so logic TTL chips might be required). Or you can simply buy them. There are a lot of integrated H bridge circuits available in the market, such as L298. The ones I use are L9110s Dual H Bridge purchased on Ebay (like this one: http://www.ebay.com/itm/350877288713?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649). They are low cost (~$2 each), compact (.8″x1″) and are powerful enough (~800mA). However, if you buy from a Chinese seller, shipping can cost 3 weeks.

L9110s is also sometimes known as HG7881.

Regarding the H bridge, you need to make sure that the continuous current limit of the circuit is greater than 500mA. Usually the stepper motor in a DVD drive is rated at 5V and each coil has a resistance of 10ohm. So the current through each coil would be 500mA! A very large current!

5. a LM317 regulator, a power NPN bipolar transistor (like E3055, should be able to handle continuous 200mA at least), some resistors, capacitors and a bundle of jumpers.
The LM317 is for the laser driver. The power NPN is for making a switch for the laser. My lab has tons of these components so I don’t have buy them. If you don’t want to solder a driver by your own, you can surely buy a laser driver for <$5. The laser driver need to be able to output at least 200mA at 2V and have the function of enable/disable.

If fact, it will be a better idea replacing the NPN bipolar with a MOSFET transistor. There are a lot of them available on the market and are very inexpensive. Just make sure that the continuous current supported by the MOSFET is above 200mA.

6. a solder gun, screw driver and some basic hard wares.

STEP 1: Disassemble DVD drives (writers)