Electronics > Microcontrollers

Reset esp8266 when alarm circuit path *broken* with minimal power draw at rest

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puterboy:
I am using an esp8266 to monitor the continuity of a loop of wire (for an alarm).
When the loop is cut, I want to awaken the esp8266 from deep sleep and process the alarm signal.
I want to minimize power drain during the deep sleep phase to preserve battery power.

Note that the esp8266 typically awakens by driving RST low (e.g., grounding it) to create a HI->LOW transition.

Basicaly I need something to "invert" the signal so that cutting (i.e, interrupting) the signal will create an output that acts as a "sink" and drives RST low.

Using a pulldown resistor alone will surely draw too much current at rest.
Other choices I have considered are:
- One-shot/Monostable chip?
- Microcontroller?
- Discrete transistor circuit?
- MOSFET circuit? (with one end of loop grounded and the other end going into the GATE with high value resistor to VCC and RST attached to SRC with DRAIN grounded so that when loop is broken, gate is pulled high and and source is driven low)

Note total loop resistance itself is about 50-60 ohms (it's a 200ft+ loop of thing gauge wire)

So what circuit & components would you recomend so that current draw is minimized when monitoring loop before cut?

CountChocula:
I wouldn't discount the pull-up route altogether, at least without a bit of experimentation. You can use a very high value resistor and end up with negligible current use.

langwadt:

--- Quote from: CountChocula on April 23, 2024, 05:14:13 pm ---I wouldn't discount the pull-up route altogether, at least without a bit of experimentation. You can use a very high value resistor and end up with negligible current use.

--- End quote ---

a very high value resistor would likely make it noise sensitive

Kasper:
I've used a mosfet for a few similar circuits.

Do you really just need to drive reset low or do you need a pulse: high -> low -> high?

If you need a pulse, an RC delay and 2 mosfets can do it.

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