Need help to understand the circuit pls.

[Chriss]

Hi!
I trying to understand a part of this circuit:


but have some problems to understand for what is the:
D1 or D2 and C1 or C2 and why are the R2 and R6 connected to Ub=12V?
Especially I'm interested in the C1 or C2 cap's, why they are in series with the B of the T1 or T2?
And the R2 or R6 why that is needed?

Thank you.
My best regards.

[T3sl4co1l]

R2 and R6 don't seem to be very useful; the transistors will only turn on when the input pins are driven with more than about 5V peak to peak.

Tim

[SiliconWizard]

This is probably some adapter made to be plugged to RS232 ports.
Pins 4 and 7 are DTR and RTS signals, and are typically +/-5V to +/-12V signals.

The diode is there to clamp negative voltages since as said above, the input signals can go as low as -12V.
The capacitor is there to form a monostable multivibrator. The output pulse (open collector) will have a fixed duration as long as the input pulse (positive) is longer than the time constant.

A common trick to ensure a fixed pulse duration here, since it's probably meant to be driven from a PC's RS232 port and the timings of the DTR/RTS signals can't be accurate.

[Chriss]

Yes, the circuit is an adapter driven from a PC RS232 port.

Thank's for that nice explanation.
My best regards.