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Press ON - Hold OFF Latching Circuit

milosrasic98

Hi!

For a project I'm working on, I want to turn it on and off using only a single button, but in such a way that when you press it turns ON, but for you to turn OFF the device, you need to hold it for a longer period, let's say 5 seconds for example. I was just wondering if you have any circuit ideas that you would like to propose. I've been looking online already of course, and have found one circuit that I will be trying, it's on this link:

http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/electronic-circuits/push-button-switch-turn-on/latching-toggle-power-switch

Fig6

So my list of requirements for it would be:

  • Press ON
  • Hold OFF
  • (Almost) No power draw when OFF since my idea is for it to be battery-powered
  • I would love to read the state of the button with a microcontroller, but the microcontroller can't be used for the latching part, I'm already stretching the MCU thin, and I would need to add an IO expander which I would rather not do at the moment.

Thanks for any tips that you have!

Milos

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    I have used a power latching circuit in a lot of my designs.  But instead of adding extra circuitry, I used existing circuits with a few added components. This works given that there is a need for a microprocessor and some other power circuitry.  In this case, a lot of my designs will have a Li-Ion battery and will also have an onboard battery charger, a 5V boost circuit and a microprocessor. Here is one such design (a 5V power pack).

    image

    The pushbutton (PB1) enables the 5V boost circuit (U3), which in turn powers the 3.3V regulator (U5) via Schottky diode (D3) , turning on the microprocessor (U4). The microprocessor checks the battery voltage and if sufficient, it latches on the 5V Boost circuit (through R15).  Now the circuit is on.  The microprocessor continues to monitor the pushbutton, looking for an extended press (I think I use 3-5seconds).  If the microprocessor sees an extended press, it removes the enable to the 5V Boost circuit and when the button is finally released the power turns off.  I use the LEDs to confirm that the pushbutton has been sensed in the long press by turning on all the LEDs so that the user knows that the unit will be turning off.  Also, the microprocessor monitors the battery voltage and forces a shutdown if the voltage drops to an unsafe level (over discharge is not good for Li-Ion batteries)

    Note, the when the USB power is supplied to the charger chip, the power is also routed to the 3.3V regulator to power up the microprocessor (but not the 5V Boost), so the microprocessor can monitor the charge process using the LEDs to indicate charging status (turning the LEDs on/off in sequence at a rate determined by the charging current).

    Not the simplest approach, but one that works well with battery powered devices.

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  • 0

    I have used a power latching circuit in a lot of my designs.  But instead of adding extra circuitry, I used existing circuits with a few added components. This works given that there is a need for a microprocessor and some other power circuitry.  In this case, a lot of my designs will have a Li-Ion battery and will also have an onboard battery charger, a 5V boost circuit and a microprocessor. Here is one such design (a 5V power pack).

    image

    The pushbutton (PB1) enables the 5V boost circuit (U3), which in turn powers the 3.3V regulator (U5) via Schottky diode (D3) , turning on the microprocessor (U4). The microprocessor checks the battery voltage and if sufficient, it latches on the 5V Boost circuit (through R15).  Now the circuit is on.  The microprocessor continues to monitor the pushbutton, looking for an extended press (I think I use 3-5seconds).  If the microprocessor sees an extended press, it removes the enable to the 5V Boost circuit and when the button is finally released the power turns off.  I use the LEDs to confirm that the pushbutton has been sensed in the long press by turning on all the LEDs so that the user knows that the unit will be turning off.  Also, the microprocessor monitors the battery voltage and forces a shutdown if the voltage drops to an unsafe level (over discharge is not good for Li-Ion batteries)

    Note, the when the USB power is supplied to the charger chip, the power is also routed to the 3.3V regulator to power up the microprocessor (but not the 5V Boost), so the microprocessor can monitor the charge process using the LEDs to indicate charging status (turning the LEDs on/off in sequence at a rate determined by the charging current).

    Not the simplest approach, but one that works well with battery powered devices.

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