|Re: HP-41C Card Reader|
Message #9 Posted by Rainer Wiedemann (Germany) on 5 Feb 2009, 4:58 p.m.,
in response to message #8 by Roy Welch
If you have a brand new IR led without already clipped leads, the longer lead is the anode, the shorter one is the cathode.
The anode has to be installed into the card reader, that the anode points towards the five colored wires, the cathode has to point towards the motor side.
The IR led is the light transmitter, the photo transistor is the receiver, if it detects IR radiation, it will switch write protection on, preventing the card reader from overwriting a magnetic card. Please note, that the IR led is pulsed for a very short time just in the right moment when the card edge passes by. So you cannot measure a permanent voltage applied to the led.
Bend the top of the led in a 30-40° angle against the leads towards the calculator side of the reader, the highest point of the led lens should be about 0.8 inches (some 20mm) above the pcb, before you solder it.
Don't forget to insulate the lead wires with a strip of Scotch tape towards pins of the integrated circuit in front of it. Otherwise the led my be bended towards the ic pins during assembly, causing a short circuit and killing the whole thing.
A short test with a clipped card should be performed before completely assembling the card reader.
Don't worry, sounds much more complicated than it actually is.