Elpro Repeater Self-Watchdog

In some instances radio telemetry systems require a repeater atop a mountain in order to have the signals relayed across the required area. Mountain tops normally lack two very important requirements, power and accessibility.

Power can be achieved by the use of solar, wind, or a combination of both. The question of accessibility is therefore the only to be addressed. It must be remembered that electronics is involved and inadvertent "lock-ups" can occur but accessibility becomes a major issue especially if all that is required is a power-down power-up cycle (total failures cannot be remotely repaired).

With some careful programming and the circuit below a power re-cycle will occur on comms failure.

Using the Elpro 105U-1 (set as Unit 10) the required mapping, as shown below, has an unused input (DI4 inverted) mapped to DO4. DO4 will therefore become active shortly after power-up. Not shown, but also programmed into the system, are the mappings of two remote units who also keep this output activated.

The timings used are important. The remote units (keeping the output updated) are programmed for 5 minute updates with the local mapping updating only every 15 minutes. The output is programmed to reset on a "no comms" at 14 minutes.

The logic is:

  1. The output is made active shortly after power-up by the local mapping. This will energise the relay to the right which will switch the capacitor across the supply via the current limiting resistor.
  2. The remote mappings ensure the output stays active by updating within 5 minutes. Two remote units are used to ensure that a re-cycle does not happen should one of the remote units fail.
  3. Upon no receipt of any updates (comms fail through e.g. receiver lock-up) the output drops, this being possible as it will time-out (14 minutes) before the next local update (15 minutes). The right side relay will drop out and switch the capacitor across the power