Friday, 4 July 2014

Optical End-Stops

posted 2 May 2014 09:13 by David Taylor   [ updated 3 May 2014 06:55 ]

When I looked at an Optical End-Stop for the first time, I noticed it had 4 pins while most diagrams show it with 3 pins. I then took one of my Optical End-Stops apart and looked inside to see how the device is wired up. In my case I could do this non-destructively, and I could close it back up. Internally the device has a small PCB which has two of the pins connected together.
I looked around for an interface circuit to make my optical End-Stops work on my 3-pin Ramps 1.4 board and found the hand-drawn diagram below by RetireeJay on the Printerbot Talk forum on the same subject.
I figured I could get rid of at least one resister and came up with the circuit below, which works just fine.

I had some Vera board lying around and made up the board as follows. which ended up being about 1.5cm x 1.5cm.

Here is a photo of the final product.

On this circuit the LED turns off when the optical end-stop is triggered and the LED's aren't super bright, but it does the job by passing about 2.3mA through the LED when it is tuned on.

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