hard disk actuator as galvo

[goosst]

Hello,

I came along this interesting topic where a galvo is made from a hard disk voice coil.
http://scanlime.org/2008/07/hard-dis...er-at-ilda-4k/

Is there someone who fully understand how the position sensing is added to his prototype ?

Position sensors: Each consists of two LEDs (one stationary, one moving) and a TSL230R light-to-frequency converter chip.

It's not very clear to me how the light difference for the TSL230R is created here (and where the two leds + chip are mounted).

thanks!

[mixedgas]

4K PPS is heartbreaking..&nbsp; If you must build a galvo, build these:<br><br><a href="http://elm-chan.org/works/vlp/report_e.html">http://elm-chan.org/works/vlp/report_e.html</a><br><br>Steve <br>

[DanBarlow]

Hello,
Is there someone who fully understand how the position sensing is added to his prototype ?
It's not very clear to me how the light difference for the TSL230R is created here (and where the two leds + chip are mounted).
thanks!

mixedgas is right, but in case it is useful info...

LEDs can be used in reverse as photodiodes.
https://en.wikipedia.org/wiki/LED_ci...s_light_sensor

It looks like the transmitting LED is mounted shining down through the hole in the voice coil, so as the coil moves it blocks more or less light.
The receiving LED would then be mounted so that it is being hit by the edge of the shadow when the arm is in your intended center position.