555resetswitches
So I am designing a circuit and wanted to implement both power and reset in one momentary switch. What I mean is, if the switch is pressed, it sends a reset signal (4.5v), but if it is held for x seconds, it powers on/off. I figure I might need a 555 timer.
How to do this?
EDIT: Some specifics:
One press when the circuit is off turns it on. It is to reset an IC (so HIGH at 4.5v).
Believe it or not, that black lump is epoxy covering an integrated circuit, probably a small microprocessor. These are often caseless chips, just the IC die glued to the PCB with fine wires between the pads on the chip and PCB.
Many microcontrollers can be put into a deep-sleep state where they draw just a few microamps, so little so as not to significantly affect battery life. They spend all of their time in deep sleep until someone presses the button, which is connected to an interrupt line to wake it up.
Bradman175 is on the right track, but perhaps a diagram that shows what he's talking about would help:
simulate this circuit – Schematic created using CircuitLab
Best Answer
A discrete analog circuit could be something like this...
Power would always be available at SOURCE and is switched via the P-MOSFET M1 to the POWER_OUT line.
Initially all transistors are off.
The P-MOSFET is gated by an N-MOSFET, M3. This MOSFET is gated either by the momentary switch to SOURCE, or via the output from the P-MOSFET. As such when you press the button M3 turns on, which then turns on M1, which then keeps M3 turned on when the switch is released.
SW1 also charges C2 to hold the RESET line high until the button is released, at that point reset will decay as C2 is discharges through R5.
Further, holding down SW1 will cause C1 to charge through resistor R1. When the voltage at the top of C1 rises above the gate threshold of N-MOSFET M2, the latter will turn on and pull the gate of M3 low, turning off the P-MOSFET which will stay turned off when the button is released. C1 will then discharge through D4 and R6 during which time you would not be able to power up again.
Briefly pressing the button again while it is powered up will simply recharge the reset capacitor.
Note the circuit itself uses zero current, other than leakage, when the button is not being held in.
simulate this circuit – Schematic created using CircuitLab