Electronics > Beginners

Circuit for generating one pulse?

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Technological:
I'm working on installing a Battery Management System for a Li-ion battery, 20 cells in series.
I'm going to activate startups and shutdowns remotely.
The BMS needs to apply voltage of 3-5 V for a couple of seconds to one of the inputs to start up after a shutdown. The manufacturer suggests connecting a Li-ion battery briefly to this input.
This input takes 2mA of current so I can't leave it connected to the battery.

I need a circuit to
- turn the output on when the input comes on
- turn the output off after ~2 seconds
- keep the output off as long as the input is on

Would anyone suggest me the simplest reliable way to implement the circuit?

I was thinking towards a 555 timer. But the complexity of implementation is significant. It would require a power supply to power the 555 from 80V battery voltage, another PCB. The parts count raise significantly. Can the circuit be implemented simpler?

brucehoult:
If this is not a "I really want to learn how to use a 555 and design analogue circuitry with long time constants around it" thread, then get the cheapest microcontroller you can find, preferably one with an internal oscillator and able to be programmed using the Arduino IDE.

My go-to for this is the ATTiny85.

When powered from 5V and running on the internal oscillator at 1 MHz they use a bit less than 2 mA, but you could presumably have it sleep most of the time and just wake up to check the input from time to time (or trigger an interrupt when the input changes). In sleep it uses 5 µA.

There are significantly cheaper chips now, but at a couple of bucks, with no external components needed (once programmed). It's not that expensive for a 1-off project.

Technological:
Learning microcontroller programming could be a more time consuming task for a 1-off project. Would you suggest how to start?

Any ideas of an analog circuit that latches off after a certain period of "on" time?

Ian.M:
A NE555 timer has a typical supply current of 2 mA @5V so there would be no advantage using one for any attempt to eliminate a 2 mA continuous drain!

--- Quote from: Technological on June 05, 2023, 11:33:57 am ---I'm going to activate startups and shutdowns remotely.

--- End quote ---
First define 'remotely'!  Do you mean over a wired link, or are you intending on some sort of wireless, infrared, or network control?  If the latter, how is the receiver powered when the BMS is shutdown?

Benta:
The MC14541 (onsemi) or CD4541 (TI) will do exactly what you want.