Battery-less IR Tower

This IR Tower design “scavenges” power from the RS232 port. For ease of construction,
I put the power supply components on a small piece of perf board in the DB9 connector
shell and the rest in a hollowed out brick. I used an old piece of 4 conductor mouse 
cable between the bnck and the connector. Functionally is is very simple. On the transmit 
side, the TXD signal from the PC “un-resets” the 555 which then makes the required 38KHz 
signal which is emitted by the IR LED - use a high efficiency type. On the receive side, 
the hard work is done by the IR detector chip, use Panasonic PNA4602 or PNA4612 removed 
from it’s metal shell (obtainable from Digikey). Overall, note that the apparent common 
ground line is in fact derived from the negative most output from the RS232 signals. If 
you use a ‘scope to check the thing out, don’t attach the probe’s ground pigtail to this 
line, you’ll lose half the supply voltage. This design is only intended to provide 4 – 8 
inches of operating range. It can be very useful in multiple RCX environments where you 
want to minimise interference to other RCXs. I have downloaded the firmware using this 
tower as a form of validation.

If you need further information, email me at barnes@sensors.com

John Barnes