Ian Birds IR System

I’ve just received the document below from Ian Bird. It’s an initial description of his exciting work on a new low-cost DIY IR distribution solution (try saying that after 5 pints).

“Infra Red Relay System Specs – This system is the logical progression from the IR transmitter that Nigel Orr published sometime in late 2000. It bears no resemblance to the original circuit now.

Aims – I wanted to produce a bi-directional hard-wired system for relaying IR signals from one room to another using a bus based communications system. Additionally I wanted to provide some feedback protection so that an emitter would not receive its own transmission and go into a loop. The following list of features now exists in the program for the micro controller and on breadboard.

Hardware – This is a PIC based system using the 16F84a running at 4 MHz. The bus is a differential RS485 based system. Inputs will be from up to three TSOP’s and output will be via two blaster and two emitter type IR LED ports. A blaster has the resistor built into the IR block and will typically consist of several IR LEDs. An emitter uses a resistor on the circuit board and would probably be of the ‘stick onto the equipment’ variety and be a single IR LED. Additionally the blaster ports can be configured as emitters by using a jumper.

The bus – The bus is a differential RS485 based system. This means that there are two wires for the bus. One carries a positive image of the signal and the other a negative image. The chips do all this and the units get out what was put in with no interference from external electrical sources. One point of note is that if the units are connected to different power supplies it may be necessary to have a common ground. This would mean there would be a minimum of 2 wires connecting the units but this could be 3 for best operation. The ideal would be two bus wires and two for 12 volt power.

Frequencies – Originally I only considered 38KHz but rapidly requests came in for both 56KHz and IRDA. After some research and experimentation I have managed to include 56KHz but IRDA was not possible. There are several reasons for this but the main one was speed. In an effort to keep costs down the hardware I am using was simply not up to the job. If implemented this will have to be a separate project.

Additional features under development – Combining the two frequency outputs and splitting them across an emitter and blaster each. This would make the units capable of receiving and transmitting both frequencies. I plan to be able to turn off feedback protection via a jumper so the unit can be used to relay an IR signal inside a cabinet. The default is no transmit on the unit receiving the IR signal.

Software notes – Once a receiver starts inputting demodulated data the system will only listen to that receiver until approximately 1 second after it stops transmitting.

Specifications
Power supply 12 volts
Processor PIC 16F84a
IR receivers Up to 3
Input frequency 2 at 38KHz and 1 at 56KHz (fixed).
IR output 2 Blaster and 2 emitter ports
Output frequency Can be either 38KHz or 56KHz. Configured in pairs as either all 38KHz or 2 for each frequency by jumper
Jumper select for feedback Enable or disable feedback protection for any unit.
Other jumpers Select processing options e.g. IR output frequencies
RS485 bus Termination supplied on all units. Only the end units in a daisy chain arrangement need this. Disabled by switches.

Accessories
IR Blaster Several LEDs with internal resistor ready for connection to the blaster port.
IR emitter Single IR LED ready for connection to the emitter port. Can be either stick on or stand alone.
IR distribution block More IR outputs for either 38KHz or 56KHz IR. Can be used with either or both frequencies as long as the main unit is outputting them.
38KHz Receiver TSOP1838 Supplied with plug and ‘x’ feet of cable.
56KHz Receiver TSOP1856 Supplied with plug and ‘x’ feet of cable.

Note This is a working document and some of the items listed are still being developed and prototyped.”

Contact Ian for more info:- [email protected]

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