Push Button ON/OFF for hand held equipment.

[latecomer]

soft on/off circuits using fet

Hello all,

I am looking for a solution for using a push button(momentary contact - soft touch) to switch ON/OFF the power to a microcontroller based hand held equipment. The circuit is powered by a battery.

Thanks in advance.

 

[Jepeto]

ltc2950 +microcontroller

You need dual contact switch, N-FET, P-FET
The P-FET hold closed by resistor
When pressed the switch bypass the P-FET and powered the CPU
When the CPU wake up “1” on the N-FET gate hold the P-FET open, “0” on the N-FET gate shutdown the power

 

[latecomer]

on off circuit using one push button

Thanks for the circuit.

My circuit current is around 200ma. Can I use a normal push button accross the FET ? or do I have to use a push button which can handle the 200ma current ?

And to shut off the circuit, can I use the same push button ?

I am looking for a circuit which will be similar tot he power button in cell phones (same button for ON and OFF)

Thanks.

 

[togarha]

push on/off circuit

Hi!

And what must we do to make the same but with a membrane keypad (p.e. 4rows x 4colums)...?

Thanks in advance

 

[Faros]

equipment on/off circuit

If I understood you correctly then you are asking for a 200 ma switch that can be a part of standard low power membrane keyboard matrix normally used for hand held equipment.

This will not be practical … if it is a hand held and you will use a battery and MCU in it then try this approach:

- Recent microcontrollers have very low power ( nano watt technology)
- Most of them have a sleep mode and also a programmable oscillator that you can switch to lower freq. for lower power consumption.
- You don’t have to switch the whole equipment OFF just switch the display and then put the MCU in a sleep mode with lower OSC. Freq. (through programming) …. Then your battery live will not be shorter than shelf live

And a simple long key press on power switch can re-switch the display and awaken your hand held equipment.

 

[artem]

hand held push button

yet another add - handheld devices use one button for both ON and OFF operations.

If you plan to use mcu in sleep mode pay attention to GPIO pins - they can sink source currents. read data sheet carefully where those cases are explained.

 

[Jepeto]

Yes miniature Push Switches have 50ma currant rating you can use larger switches or to power only the CPU, when the CPU wakes up it powers the rest of the circuit with additional FET
If you use DPDT switch the second contact monitored by CPU when the switch pressed the CPU shut off the FET when the switch released the circuit power is off

 

[Faros]

Dear friends

He can use only one I/O line say PortB 0 or 4 to 7 where any can be assigned as interrupt line, the current will be very low and can be neglected, pull up any line with 10k and you will have .5 mA ... nothing to worry about ... I have tested that.
no need for FET's or any other switching device.

 

[jmarkwolf]

Hello all,

I am looking for a solution for using a push button(momentary contact - soft touch) to switch ON/OFF the power to a microcontroller based hand held equipment. The circuit is powered by a battery.

Thanks in advance.

Have a look at the Linear Technology LTC2950 chip. Cute little bugger.