The RXB4411S-418 (RF receiver module) and the STPA (RF transmitter module) units available from Circuit Specialists are powerful, easy-to-use RF modules that make adding wireless control or signaling capability a simple matter. They are essentially self-contained modules that require no other external components aside from an antenna and a power source (battery). These modules use the 418 MHz license-free industrial band operating frequency.
A brief example will be presented to demonstrate the simplicity of using these devices. This example is for a wireless annunciator — a doorbell — that may be battery-operated and will thus be located in an area where no power is available. The circuit consists of a 555 timer circuit that generates an audible tone. This circuit could be any type that generates a square wave signal that can be used to modulate the STPA transmitter module. Since the STPA has a built-in antenna, the only external components required are a 9-12 volt battery and an on/off switch.
The transmitter is capable of relaying the signal over a range of several hundred yards, depending on the terrain. The receiver section is equally simple and requires only an external antenna and a power source. The external antenna can be a commercially available antenna or a basic length of hook-up wire. The receiver module has two output ports, analog and digital. I used the analog output port for this application due to the ease of interfacing. The analog output is fed into an audio amplifier (such as the 18W Audio Amplifier kit – KIT 150 available from Circuit Specialists). This will amplify the received tone and drive a loudspeaker to signal an alert.
The RXB4411S-418 receiver module and STPA Transmitter modules can be used to create a simple wireless signaling system using either analog or digital signals. A digital signal implementation of these devices would require a slightly more complex circuit since the wireless protocol desired would need to be implemented with additional circuitry.
The parts list for the representative circuit is as follows:
QTY Description Part Number
1 RF Module (RCVR) RXB4411S-418
1 RF Module (XMTR) STPA
1 555 Timer 555
1 PB Switch R18-29A RED
1 Polystyrene Capacitor 23BK247
2 Ceramic Capacitor 21ET100
1 Resistor ¼ watt 510K RA510K
2 Resistor ¼ watt 1.0K RA1.0K
1 9 V Battery (or AC/DC adapter)