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AN #164 - Radio Range Detector Print
by Don Owen

The purpose of this system is to check the range and reliability of low powered radio links. The Transmit unit comprises a Mega8515 micro, a Holtek encoder chip

HC12E and an RF module ZW3100 TX (433.92MHz). However, virtually any RF Transmit module can be substituted here as long as it is compatible with its corresponding receiver. The Receive unit comprises a Mega8515 micro, a Holtek decoder chip HC12D and an RF module ZW3102 Rx (433.92MHz). The system operation is usually arranged to have a fixed location for the Transmit unit while the Receive unit is moved around until data is no longer reliably received. For low power units a reliable range is typically a little over 100 meters.

Transmit unit:

This is arranged to output a pulse from a port on the Mega8515. The pulse occurs once every 5 sec and lasts for 0.5 sec. A mark/space ratio of 9:1. This pulse activates the HC12E to output data in the 0.5 sec interval, which in turn modulates the ZW3100 Transmitter.

Receive unit:

The ZW3102 in the receive unit outputs the demodulated data for decoding by the HC12D which when successfully decoded produces a momentary high level from the decoders VT pin as well as latching the 4 data bits. These 5 lines are then fed to the Mega8515 for processing and the result is displayed on the LCD which shows a good/bad count as well as the data corresponding to the 4 data lines in decimal form (0 to 15). Timing is under the control of the Mega8515. The addresses for the encoder and decoder must be the same. The circuits of the Transmit and Receive units show the addresses hard wired for simplicity, as are the 4 data lines.

Operation:

The transmit and receive units are placed near each other for synchronizing purposes as there will be no good/bad count displayed until this occurs. The portable receive unit is then progressively moved away from the transmit unit until “bad” counts are displayed by the LCD. The actual data value as per the value in the hard-wired transmit unit is also displayed.

Other aspects:

Further enhancements to this system could be made by using a piezo buzzer connected to a Mega8515 port and programmed to produce a sound when a “good” pulse is received. As the system was made up using boards that were previously used for other purposes, the micro connection groupings probably appear strange. The programming may appear to be a little clumsy by experienced programmers standards but the system as described proved to be very reliable.