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inputs
The binary inputs are designed to be used with contact switches and no other external components. They're actually doing you a favor, but it makes it a little harder to interface TTL level inputs.
If you want to connect a switch to a pin on the stamp (not the RC) you'd need a pull-up resistor so that the pin has a stable value. When the switch is closed, the pin is shorted to ground.
The pin is internally inverted byt the RC so it sees a 0 when the switch is open and 1 when its closed. Since the input is already pulled up to +5V, applying a voltage to it won't change the value. If you apply more than +5V you'll fry it.
If you have an external circuit that you want to interface with the binary inputs, you'll need to use a component that acts like a switch. I'm sure there are other ways to do it, but I know that an NPN BJT (bipolar junction transistor) as an open-collector switch works fine. You connect the binary input to the collector pin, a ground to the emitter pin, and your logic signal to the base. You also need to connect a ground from your external circuit to the emitter pin. When your signal goes high it closes the switch and when its low it opens it. You can get a pack at Radio Shack for a few bucks.
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