Hacking CD-ROM Player Part I

The CD-ROM player (or DVD player) is a nice source for electronic parts and hacking. You can also learn a lot by taking a CD-ROM player apart. I do want to warn for the laser. If you have the player open and hook it up to power, make sure you disconnect the cable to the head with the laser. Work on your own risk, I'm not responsible.

Without hacking you can still get some nice parts out of the player, here are some examples:

- DC electric motors. Probably even two of them, one for opening the CD bay/tray, the other for moving the laser head;
- Some small things, like buttons, LED's, cable (and connector). Also jumpers and audio connectors can be found;
- Big electric motor, also BLDC called. It also has a strong magnet on it;
- 40Mhz crystal;
- hall effect sensor.

I have forgotten the laser, but it is dangerous. Damage to the eye cannot be fixed.

Al right, let's hack something. First we begin with something simple. The two DC motors look like fun and don't require much power to turn, you can easily run them directly on an ATtiny13, but I advice to use an extra transistor that gets the beating.  The ATtiny13 can serve as a PWM generator.

I have a nice and simple setup to do this:

The big cable junk is just to program the ATtiny13. The long green wire goes from pin 2 (PB3 in code) to the NPN transistor base. The transistor is a BC549C, it can hold max. 500mA. There is a small diode at 25 to prevent things going wrong. The two 10 Ohm resistors is where you connect the plus of the DC motor. You can use this schematic also for a LED or buzzer.

Let's get some code to make simple PWM. I'm using Assembler. There will also be a post/tutorial on programming in Assembler.

.include "tn13def.inc" 

.def mp = r16
.def temp = r17
.def t1 = r18
.def t2 = r19

rjmp main			; go to main

delay:
	clr t1			; clear register
	clr t2			; clear register
	ldi temp, 10		; set register temp (r17) to 10
delaywalk:
	;dec T2		; 256 x 3 x 10 = 7680 cycles
	;brne delaywalk	; uncomment these for longer delay (+160 ms)
	dec T1		;
	brne delaywalk	; standard ATtiny13 clock is 9.6Mhz
	dec temp	; 9.6Mhz/8 (divider) = 1.2Mhz a cycle
	brne delaywalk	; total delay time = +/- 6 ms (with temp on 10)
	ret		; go back to where you came from

main:
	ldi   	mp,0b00001000	; set 8 bit binary (note 8 numbers)
   	out   	DDRB,mp		; set pin 2 or PB3 to 'on'

loop:

LDI   mp,0x00     	; set register mp (r16) to value 00
OUT   PORTB,mp		; put 00 (low) value to port, means off		

rcall delay			; jump to/call delay

LDI   mp,0xFF     	; set register mp (r16) to value 255
OUT   PORTB,mp		; put 255 (high) value to port, means on		

rcall delay			; jump to/call delay

rjmp loop			; jump back to loop

To make ON time longer than OFF time, you can simply put 'rcall delay' two times in the code or make a new delay branch.

That's all for part I.