IR Transmitter Circuit

Hi All,

I have been looking at Nigel Goodwin's PIC tutorial, particularly the infrared circuit.

I have attached the circuit but removed the receiver element as I am particularly interested in the TX.

I understand what it all does except for the reason for why R4 is brought to GND, a potential divider? why couldnt R3 and R4 be in series with the base of the transistor?

Thanks

Mark

Aha! let me try and answer my own question, is this a "pull-down" resistor?

Mark

Yes!

It helps turn the transistor off, by discharging the base charge.