Christchurch, NZ
MReX-PCB User Guide V1.02
LED/Piezo Resistor Configuration
The following resistor configuration information describes how to modify the MReX-PCB if LEDs
are to be used powered directly from the fitted AAA battery pack, or how to fit a piezo sounder (and
required components).
R1 is used to limit current through the green LED/Piezo. Typical LED value resistor value from
220R to 470R. When a piezo sounder is fitted R1 = 47R.
R2 is used by the piezo to improve audio response (1K typically). The resistor fitted should ideally
be selected to produced the greatest audio output.
R3 is used to limit current through the Red LED. Typical LED value resistor value from 220R to
470R.
When the command *RX_ENABLE=0 is sent to the MReX (disabling the receiver), the green LED
operation changes so that instead of flashing once a second, this output is modulated, so that when
connected to a piezo sounder, a beep will be heard prior to input activated transmissions.
© WTE Limited, 2021 – Christchurch New Zealand
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