Using the Circuit Specialists RXD4140-434 and STPA RF Modules

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)



George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

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