Transmit Infrared Signals Through Walls
or
How to turn your IR transmitter into an RF transmitter & control stuff throughout your house

Project update: The project has been revised to work with the newer Linx Technologies LR series.

Please see this page for the new project http://www.rentron.com/NEW_IR_TO_RF.htm We will be removing this older project page shortly, so please update your bookmarks.

I get "TONS" of requests on how to do this, so I've finally put together this simple project showing you how to use your existing infrared transmitter from any room in the house. The principal is really pretty simple, and it works better than you would think.

This is a "very handy" little project. With this gadget you can control anything from pretty much anywhere. Even place your stereo equipment inside an enclosure then use your existing IR remote control without line of sight. Adjust the volume on your stereo from other rooms in the house. You name it -- so enjoy...;o]

I have tested both circuits with TV's, stereo's, and various VCR's & CD players. I can change channels, adjust volume, etc, from any room in the house (and outside) where I have the IR to RF circuit in Figure #1. The RF to IR circuit in Figure #2 is placed on a bookshelf across our living room, and aimed in the direction of our TV & stereo.

Note: You can place the IRLED on long wires to extend it right onto the front of the equipment you need to control and do away with the Zetex 603 High-Current IRLED drive circuit. I'm a little power hungry, and always like to see just how far I can push the envelope, but you may prefer to tone this down a bit. You can directly drive the IRLED with a single series resistor on the 40kHz modulating PIC for much shorter range operation.

If you're placing the receiver & IR LED close to the equipment you'll be controlling, you do not need the high-current NPN LED driver circuit.

How It Works:

We'll use our existing infrared remote control transmitter for our TV. We'll transmit to the IR detector shown in Figure #1 below. The IR signal from our transmitter is output on the TSOP-1140 40kHz IR detector module data output pin (labeled RX DOUT) in Figure #1.

The IR detectors output signal feeds data to the input of the TXLC-315 RF transmitter module through the 2N3906 PNP transistor inverter circuit. When no data is being received from the IR transmitter, the PNP transistor & TXLC-315 RF module are both OFF.

We need this inverter circuit since the TXLC-315 data input needs to be held at ground during idle (non-transmit) periods. The output of the TSOP-1140 IR detector idles at logic 1. Applying this logic 1 directly to the TXLC-315 data input would cause the TXLC-315 RF transmitter to always be ON. We don't want this. We only want incoming data from the IR transmitter to turn ON the RF transmitter to re-create the same signal the IR transmitter is sending. That's the purpose of the PNP inverter circuit.

In essence, we're simply turning IR into RF since the IR detector output will now modulate our RF module thereby re-creating the same signal, but now it's RF instead of infrared. We use our IR transmitter to send data from any room in the house by installing the circuit shown below in Figure #1 on our TV IR transmitter, or building one of the circuits shown in Figure #1 for each  room.

Figure #1: Infrared Receiver to RF Transmitter Circuit

Now all we need is the circuit that receives the RF signal, then re-creates this same data signal in infrared. The circuit shown below in Figure #2 does exactly what we need.

Note: We've revised the RXLC-315 circuit boards. These are now 5-pin VS the old 4-pin boards. We've included a link to the older version board (and old version RF-TO-IR IC) for this project below. Anyone using the newer 5-pin modules & PIC10F200 RF-TO-IR IC, refer to Figure #2.

For The OLD Schematic click HERE

Figure #2: RF Receiver to Infrared Transmitter Circuit

How It Works:

The RXLC-315 RF receiver module receives the incoming RF transmission from the TXLC-315 transmitter. The RXLC-315 outputs this incoming data stream to the DIN pin of the 8-pin IC labeled RF-TO-IR shown above in Figure #2.

The 8-pin IC is a custom programmed PIC10F200 that samples the data input pin labeled DIN, then re-creates this same data signal modulated at 40Khz. Presto. We now have turned our incoming data back into a modulated IR signal, and we now have a standard TV or other appliance IR transmitter we can use anywhere in the house with our existing stereo, TV, CD players, etc, etc..

To assemble the code below you'll need the Microchip MPASM assembler, a PIC programmer, and, of course, a PIC10F200. If you don't have all this stuff, don't worry, we're tossing in the pre-programmed PIC free of charge with a bunch of other components for this project. See below for details.

You can download the MPASM assembler from http://www.microchip.com free of charge. It's included in the MPLAB IDE.

The RF-TO-IR Firmware: