The RL03TX and RL03RX is a transmitter / receiver pair for reliable medium range transmission of data specifically designed to relay reliably sensor information over a reasonable distance. The boards do not transmit or receive themselves but handle the data so that an easy interface to a host microcontroller can be achieved. 

The TX_SW is a small transmitter with battery holder (4LR44, 6V). This can also accommodate a PIR movement detector or door switch.


The range depends on which receiver is fitted. The typical scenario for this kind of device is a sensor in one room (or outside) and a sensor in another room or in a detached garage say. Here are some empirical results:



Quite Good


Not That Bad


Based on the MAX1473 Based on the SYN500R Based on the SYN470R Based on the LM358

Different Performance of Receivers.

  1. The best receivers are based on the MAX1473 for example, Aurel RX4-MM5, these give outstanding results, so much so it was not possible to get into a position throughout the property where a signal could not be received. The range on these is quite easily 100m.
  2. Next up are the receives based on the SYN500R. These are less expensive than 1 and achieve nearly the same performance, for most situations these will be quite good enough.
  3. The STN470R receivers are low cost and give reasonable results.
  4. LM358 Based, these always come with a transmitter. The receiver is useless and should be thrown away, however the transmitter is perfectly okay and works well with the 'good' receivers


As there is likely to be one receiver and several transmitters, stick to the MAX1473 or SYN500R. For extra transmitters buy the cheap LM358 TX/RX pair and throw the receiver away.


There are lost of information about this on the web, however at 443MHz a piece of wire 170mm long (between 164 and 173mm) works in the tests carried out. This can be a straight piece or coiled to fit into an enclosure. Better results should be obtained using a straight 1mm dia wire however any old bit of wire gave perfectly acceptable results using the set up at 3 above.

** For superior results (tested) use a ground loaded antenna as this pdf


When connected to a Raspberry Pi the receiver did NOT WORK ***(see UPDATE) at all. After conducting lengthy tests it was found to be due to interference from the Pi which was not shielded in any way. Unfortunately no test equipment was available to determine the actual source of the interference but when using another device to receive the signals for testing purposes just, connecting a short length of 4 way ribbon for the I2C interface to the RPi connector stopped the receiver from receiving.

The ribbon cable also incorporated 2 extra wires for a power supply and it was found that when the ground pin (pin 9) on the RPi GPIO connector was connected to this wire it stopped the receiver working. It should be pointed out that just a wire was connected to it, the Pi was being powered at that time form the USB. Placing a ferrite ring on this wire made no difference.

The wire (connected to the power) was about 230mm long, reducing this to 100mm cured the problem for this test setup.

It doesn't stop there though, when removing the power wires an connecting the receiver to the RPI via the I2C it stopped receiving again. It was tried with a wi-fi connection and an RJ45 connection just in case the wifi was causing the problem. Also a longer I2C lead made no difference as we can deduce from above that the interference looks like it is emanating form the GPIO connector.

An interesting note to end this sad story is that when the RPi is booting the receiver manages to get a few packets in. It is only when the Rpi is fully booted that it stops the receiver from working. Note also that it has only been tested on this one RPi which is an original version so it may work on other RPi's

******* UPDATE

Tested on a newer version Pi 2 model B V1.1 without any problems so take care with the original Raspberry Pi 2011 version!!!