Strobo controlling with PC using RS-232 port

This circuit shows a simple way to interface a commercial stroboscope with 10V remote trigger input to a PC computer so that a computer program can control the stroboscope.

Circuit

This circuit is designed to be connected to the 9 pin RS-232 connector of your PC. It gives a 10V output pulse for controlling stroboscopes which have standard remote triggering input in them.

9 pin RS232                         6.3 mm phone jack to
connector                           stroboscope trigger input
                1N4148
TXD  3 ------------|>|-------------- Tip

GND  5 ----------------------------- Shield

Circuit operation

The circuit operates in the following way:

When the RS-232 port is in idle state, the TXD pin is in logic 1 state, which means that it has around -11V potential in it. There is n
When the RS-232 port TXD pin goes to logic 0, it get the TXD pin goes to aroun d+11V potential. Now the diode will pass the current to the output jack and the stroboscope will get around 10V voltage.

The serial port goes to 0 state friefly when some data is transmitted out of the serial port or break signal is sent out.

Software to operate the circuit

There is no special software available for controlling the circuit. For simple tests you can start any communication software, select the serial port where the circuit is connected and then set the communication speed to 1200 bps. Now every time you press a key (dend character out) the stroboscope will flash once.

Ideas to improve the circuit

If you are ofraid of spikes entering from the lighting system to the computer, then add some overvoltage protection to the circuit. You can for example put a 12-20V VDR, Tranzorb or similar overvoltage protection component between the tip and shield of the phone jack.

Tomi Engdahl <[email protected]>