Opto End Stops not working

I'm making the opto endstops, but they don't seem to be working.

As I'm in Australia I could only get hold of the ZD1901. I'm building the endstops as per Vik's instructions at [dev.www.reprap.org]. However, when I test is by hooking it up to +5V it get 0V on the signal pin with the switch open. When I close it I only get ~0.01V.

-Mark

If the LED side of the optical interrupter is infrared you might be able to tell if it is lighting up by pointing a webcam or inexpensive digital camera at it. They usually have some sensitivity in the infrared. Test the camera with a TV remote control to see if it is sensitive to IR.

Yeah I already tried that. The led is definitely turning on.

I don't really understand how the circuit is supposed to work. The signal pin never seems to be pulled high.

In my understanding there should be another resistor from the signal line to high. That way when the switch is open(ie transistor is conducting) you get a logic low, and when the switch is closed(ie transistor is not conducting) you get a logic high.

Can someone tell me if I am going in the correct direction with this.

The only way that this would work was if the uC interprets a not connected as a logic high.

This is really bugging me.

-Mark

Yes you need a pullup, it's on the opto board IIRC.

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[www.hydraraptor.blogspot.com]

Yeah I put a 10k from signal to +5V and it looks good now.

*Goes to change the wiki.*

-Mark

Edit: Looks like I don't have edit privileges. Can someone who does please change [reprap.org] and add something about a pull up resistor

Edited 1 time(s). Last edit at 07/02/2008 09:33AM by batmark.