-----BEGIN PGP SIGNED MESSAGE----- - IR / RS-232 Transceiver - 96/04/23 15:05 FILES: ir_box3.txt - this file ir_box3.ps - schematic diagram UNIX sum of ir_box3.ps: 13158 192 UNIX sum -r ir_box3.ps: 20767 192 The IR / RS-232 Transceiver module will convert the signal from a UART port into infrared (IR) format, and from IR back to UART format. It will handle baud rates from 300 to 38400 baud. The IR format supports half-duplex communications only. The IR signal is compatible with the HP48 series calculators. Although I have not tried, the IR signal closely resembles the IrDA format, and I suspect this module should be able to talk to laptop computers and other devices with an IrDA port. The RS-232 port is a DTE port, which means it can be plugged directly into a modem or serial printer. For connection into a PC computer, a null modem cable is required (the wiring diagram is included). The IR format dictates half-duplex communications. The module will enforce this by disabling the IR receiver while the IR transmitter is transmitting data. The module can use either a 6V battery or a 9V battery. A 6V battery (like 4-AA cells) will last longer, but the regulator is bypassed. I find a 9V battery is more portable. The current drain is 60mA idle, 70mA during file transfer. Don't plug the 9V battery into the 6V connector. That would be bad, very bad! The basic design is based on the document at "http://www.ee.ualberta.ca/~charro/cookbook/optic/HP48SXIR.asc" by Tony Duell (ARD@PVA.BRIS.AC.UK). The IR transmitter and IR receiver runs on a 16x clock source for the desired baud rate. U1A, U1B, U2A form the cristal oscillator. C2 is critical. The 2.4576MHz crystal do not like to oscillate at its fundamental frequency (at least the ones I tried don't). C2 will suppress the overtones. U3 and U6A form the 16X baud rate generator. The baud rate is selectable using S1. The IR transmitter is quite simple. It will send a 1/2-bit wide pulse for every SPACE on the RS-232 port. The IR receiver uses U1, C4 to shape the IR pulse going to U6B pin 4, and to create a reset pulse to synchronize U5A with the UART on the IR side. When the IR transmitter is active (D1 is on), Q1 is disabled by Q2. For a short duration after the D1 switches off, Q1 will still be saturated and require a recovery period. This is provided by C3, R5. Four LED's show the status of the RS-232 DTE interface. The Tx, Rx, CTS, and DSR lines are monitored. DTR and RTS lines can be pulled high, or left unpowered. This is selectable using S1. I chose a DTE pin-out for the RS-232 port because this allows me to plug the module directly into a modem or serial printer. A null modem cable is required to connect to a PC. The wiring diagram for this is included. My next project will be a DAT cassette size serial/parallel converter so I can use my EPSON printer from the HP48. Enjoy, Tom Wong (tomwong@bnr.ca / tomwong@nortel.ca) - - ----------------------------------------------------------------- Changes: - -------- ir_box3: added a missing wire to the schematic ir_box2: added a warning about 6V/9V connector ir_box: original copy -----BEGIN PGP SIGNATURE----- Version: 2.6 iQCVAgUBMX0r6N3Bn6FMP/1JAQHMmQQAnriDuvfyy4P6JBsvq6Y3DobIkAflttqX T61aSglLzsU/qHTVmwjtSk8zzwz7R3Pb54W/VTJRFLVkTgx57OvvehEJgoeJY2nK pYx80b51JKYTVG6cirN6yuLK2TNfOjV7stcxbYsIjDRIco0pa8+Qy8BgA5ZP4g8C 5hH+2evv2c4= =Py93 -----END PGP SIGNATURE-----