FMS Forum

by **trentcollins** » Tue Jan 28, 2003 8:12 am

On the serial pic interface (12C508A)
the two transistors KT3107 are shown as a PNP and an NPN. Is this correct?
Can you get different transistors with the same number, or are they both NPN/PNP
Thankyou

by **trentcollins** » Tue Jan 28, 2003 8:18 am

XP. I presume that I connect the output from the circuit to the outer pin on the JR plug and the ground to the inner pin.
Any help would be greatly appreciated
Thankyou

by **Steve Lewin** » Tue Jan 28, 2003 9:20 am

I guess you're looking only at the 12C508 - 9pin cct. On the other 3 diagrams the NPN transistor is correctly identified as a KT3102. Any small signal NPN and PNP transistor with a reasonable gain will do.

The INPUT to the cct is from the transmitter. It does not work well with JR as drawn. If you move R5 to the other side of R4 and connct it to Vcc not ground it will work better. On the Tx connection Ground (outer) goes to ground, signal (tip of jack) goes to input.

Steve

by **trentcollins** » Tue Jan 28, 2003 9:43 am

Steve,
thanks for your help, I'll build one tomorrow and give it a try.

by **trentcollins** » Tue Jan 28, 2003 9:45 am

One more thing
Where does the 5v Vcc power come from. Can you get it from the transmitter, the serial port or a seperate power supply?
Thanks
Trent

by **Steve Lewin** » Tue Jan 28, 2003 10:43 am

The circuit as drawn does not need any external power source. That's what R3, C1 and the zener diode D1 are for, to produce Vcc from the voltages available at the serial port.

Steve

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transistors on pic interface - Are they NPN or PNP

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