Sunday, May 10, 2015

Voltcraft VC840 RS232 interface circuit

Q0 is a photo-transistor which receives IR light from a multimeter. If Q0 is illuminated then current flows through R1 and turns Q1 and Q2 on and the output R will be pulled down to positive voltage, this means mark will be transmitted. If Q0 is not illuminated then there will be negative voltage at the output R so space will be transmitted.

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