This project functions as a simple strobe for driving an LED. The use of an output transistor allows it to pulse the strobe LED with a current up to 100mA.
Four jumpers provide options for changing the pulse width, strobe repeat interval and single or double strobe flash. The programmer ready code has default timings which are easily customised by editing values in the PIC's EEPROM at programming time.
This is one of those applications where it's arguably better than a 555 timer based solution but in practice you could build it with a 555 timer faster than you can write the PIC code. However it only needs the code writing once, I've done that and designed a small PCB too so away you go.
Schematic
The circuit provides a LED strobe function with jumper selectable operating modes.
The strobe interval can be configured using 4 jumpers for 1,2,3 or 4 seconds; strobe on time of 30mS or 100mS and single or double strobe pulse.
Since the PIC can only supply 25mA from its I/O pin a transistor is used to increase the maximum current driven through the LED. This transistor has a maximum collector current of 100mA which is adequate for driving most types of 5mm LEDs. The PIC could be used to control a higher powered output switch if desired.
The value of R3 series current limiting resistor for the strobe LED has been selected on the conservative side rather than providing maximum brightness. With a 5 volt supply and LED with 1.8V forward voltage yields current of approximately 47mA.
Download schematic in pdf
Download hex file
Download source code