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Old 04-05-2012, 02:36 AM #1
Lab Lab is offline
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Question Reading data from CD laser unit?

Hi everyone,

I've recently disassembled an old Phillips portable CD player. The laser unit model number is VAM 2103/08, which very closely resembles the unit located at this link: Audio Spare VAM2103/01 (VAM 2103/01) - CD LASER UNIT (PICK UP) (MECHANISM) PHILIPS. I could not find any data sheets or schematics on this particular component.

There are 18 pins/connection points accessible to the laser component via an orange ribbon as you can see in the middle picture from the link I listed above. I've correctly identified the pins and polarity that produce laser output, as well as 2 sets of pins that seem to be fine adjustments that move the laser head slightly up/down or left/right. What I can't seem to figure out is how I can test for data or lack of data (0 or a 1) being transmitted back to the unit from the laser refractions of a CD. Specifically I've been looking for a signal change from 2 of the remaining unidentified pins.

My understanding on this is that there is some sort of a light sensor built into the same component as the laser unit that sends a high or low signal when a laser is reflected/refracted or not through a set of these remaining unidentified pins.

I've tested the remaining pins for a signal by hooking up the pins to the digital input of a Velleman K8055 card (an electronic/programmer hobbyist external USB card that interfaces to your computer to send/receive/analyze both digital and analog input or output). While I do this, there is a CD connected to the unit, and I apply 3V to the laser for the entire duration of my testing. I spin the CD with my hand slowly and check to see if the two pins I'm testing show any sort of signal change. The USB interface I'm using has a counter on the digital input I use, so any quick changes will cause the counter to increase. So far all I have found is that two of the unidentified pins can be connected to any of the other unidentified pins and always have a signal, but the signal never fluctuates. I've made sure to set the laser head is near the middle of the CD so that there should be variable data (both 0's and 1's on the CD) present near where the laser is located.

Does anyone know what pins check for the lasers reflected signal or what I have left out in checking for this? I'm not formally trained in electronics, so if you notice I'm missing some basic steps in my tests, or that I'm misunderstanding how the laser is read, please let me know what I'm doing wrong.



Last edited by Lab; 04-06-2012 at 10:47 PM. Reason: Clarify this is a question
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cd player, light sensor, pins, read data, reading cds





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