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Pushpin Computing
Responsive Environments Group

IR-to-RS232 Converter Communication Module

The IR-to-RS232 converter communication module allows a Pushpin to act as a go-between for a desktop PC and the remaining ensemble of Pushpins. It is tethered to both a 9VDC power supply and a standard RS232 serial cable, as well as equipped with a single IR transceiver identical to those found on the four-way IR module.

Schematic Diagram

Printed Circuit Board Layout

Parts List for 1 Piece
Vendor Vendor Part # Qty. $/Unit Description

Newark 32C5876 1 $3.12 Analog Devices ADG733 CMOS low voltage triple SPDT switch in a TSSOP form factor used to switch between IR and RS232 modes.
Newark 83F8851 1 $??? IrDA transceiver.
Digikey H2258-ND 1 $??? 9-pin 1mm pitch header for connecting with the processing module.
Digikey P???GCT-ND 1 $??? q0603 ???Ohm resistor used to determine intensity, and hence range, of IR transmission. Recommended range is 100-1000 Ohms.
Digikey PCC???CT-ND 1 $??? ???pF ceramic capacitor for determining the baud rate at which this module is able to receive an infrared stream. Specifically, the duration of a single infrared pulse should be 10kOhm * CpF, where C is the value of this capacitor as measured in pico Farads.
Digikey 311-0.0GCT-ND 4 $??? 0Ohm jumper.
Digikey P10KGCT-ND ??? $??? 0603 10kOhm resistor.
Digikey MM74HC221AM 1 $??? Monostable multivibrator for properly conditioning the signal generated by the infrared receiver. Guarantees a uniform pulse width for signals that would otherwise be too short.
Digikey 296-1095-1-ND 1 $??? Single inverter reverses signal polarity of the processing module's UART transmit line for compatibility with the infrared transmitter.
Digikey CP-002A-ND 1 $??? CUI Inc. CP002A 2.1mm DC power jack to be used with a 9V wall wart.
Digikey LT1121CN8-3.3-ND 1 $??? Linear Technology LT1121CN8-3.3 voltage regulator for converting 9VDC to 3.3VDC.
Digikey MAX233CPP-ND 1 $??? Maxim-IC MAX233CPP dual RS232 level converter in a DIP package.
Digikey A2100-ND 1 $??? Amplimite 745781-4 DB9 connector connects to the PC serial cable.

Last Updated: 01-DEC-2004
MIT Media Laboratory