In order to receive the FingerPrint that is transmitted in the databurst, you need to build the circuit shown here.
After you have built the hardware, you will need to calibrate it and acquire the software.
The FingerPrint Decoder must be able to select either bit polarity in order to operate with all receivers. Bit polarity is selected using a DPDT switch. The decoder must accomodate either a balanced or unbalanced type of discriminator. It uses a dual op-amp with the first op-amp providing some gain, and an adjustable level shift for the incoming data signal. The level adjusted polarity selected data signal is then passed to the second op-amp which uses positive feedback to provide hard clipping of the data signal. The second op-amp outputs an RS-232 compatible binary data stream which drives the host computer's serial input data line. Power for the op-amp circuitry is obtained from the serial port connector.
Created: 1999 May 23 Last Modified: 2002 December 7
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