I am not an electronics wizard but couldn't it use a circuit something like the old Westinghouse Bridge rectifier? Regardless which polarity the battery is connected DC can only flow in one direction. Because the applied voltage will be DC either a gate or even a transistor in one leg could be used to pull a logic pin up or down to select one or other language circuit.
One cool thing is that it eliminates a switch and any attendant reliability issues. The identifier has what appears at first glance to be a belt clip over a rectangular depression in one face of the device. It turns out to be part of the sensing mechanism. You slide one end of the bill under this clip like arrangement which trips the turn-on mechanism and it either announces the denomination or beeps a code or vibrates a code depending on a switch setting so it can be confidential and can be used by the deaf-blind. So far I am impressed. Of course had they designed a more robust tactile differentiation it would all be unnecessary. ----- Original Message ----- From: Tom Fowle To: [email protected] Sent: Wednesday, October 29, 2008 1:04 PM Subject: Re: [BlindHandyMan] News from CPSC - Two Recalls Dale, That's a cute idea, first means of doing it that comes to me involves a so-called bridge rectifier directly off the battery with a single seperate diode that would feed a voltage to some pin in one direction and not the other. Only problem with this scheme is the rectifiers cause you to "lose" a volt and a half of supply voltage. There may be a more modern voltage regulator of the switching type that does a better job. clever design. Tom Fowle [Non-text portions of this message have been removed]
