Alt-BEAM Archive
Message #00102
To: beam@corp.sgi.com (mailing list)
From: Benjamin Edward Hitchcock beh01@uow.edu.au
Date: Tue, 2 Feb 1999 12:41:32 +1100 (EST)
Subject: [alt-beam] phototransistors
I just pulled a photodiode/phototransistor pair out of an old Amiga mouse
I had lying around, and want to put them on a BEAM bot to sense walls.
The diode is no problem, I guess it works much like a LED.
But that danged transistor! Here are the voltage drops:
1 to 2: 1.9 V
2 to 1: 0.8 V
1 to 3: 1.6 V
3 to 1: 0.65 V
2 to 3: 2 V
3 to 2: 0.6 V
I have gotten it to sense the diode, when measuring pins 1 to 3.
When the
diode switches on, the transistor reads open circuit, but when it switches
off, the transistor reads 1.6 V.
I was wondering if I was supposed to bias a leg or something?
What's the best way to use one of these things? I mean, they have three
legs for a reason, right? I'm stumped. I thought giving it some IR would
make it conduct better, not worse...
Ben
--
Nothing is foolproof to a sufficiently talented fool.
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