The original switch; is it just a momentary contact on each push, or is it a mechanical push-once for on, push again for off, where the contact is closed for the entire time the computer is on?
I would rather not use mechanical as its another point of failure over time.
Hey Mike, yea that would work and it has a USB port but the machine would need a hard reboot if there was a power failure because of other components inside. Good thinking but.Can you use a Form C (three-terminal, normally-open, normally closed) switch for the remote switch?
Does the computer have a USB port? If so, you could use the presence of +5V at the USB spigot to determine if the computer is on or off. This could be use to synchronize the state of the computer with the state of the external switch after a power failure and auto reboot.
But won't you be using a mechanical switch to trigger your proposed circuit?
Be that as it may, here's one way to provide a fixed-width negative pulse whenever a SPST (or SPDT) switch changes state. A non-retriggerable monostable IC debounces the switch. You may need to adjust some of the component values to suit your situation, e.g. C3 could be bigger for better debouncing.
View attachment 70330
Just open the .asc file in LTSpice and click Simulate/Run. The simulation goes very slowly because of the 74HC221 (monostable) model used. If you take the operation of the 74HC221 on trust, just delete R5 and the sim will run much quickerI downloaded somthing called LTspice to see how that would work and i couldnt even work out how to flick the switch to see what the circut does!
epicfatigue said:I would rather not use mechanical as its another point of failure over time.
V2 represents the input being switched, by whatever sort of switch you choose, repeatedly to 5V, 0V , 5V, 0V........ The Q output of the monostable produces, at each switching operation, a positive-going pulse output , but if you look closely at the waveform you will see the voltage (which is taken from the Not-Q output) is a negative-going pulse. Either one could be used for relay control, but the Not-Q one should be able to drive the computer switch directly (assuming the supply voltages of the monostable and computer match).when voltage is applied v out will pulse 5v (if connected to a relay this would open then close) and if voltage then would stay stable. And then if it was to be interrupted (me turning off the switch) V-out would then pulse 5v again
epicfatigue said:Adding a way to trigger a momentary switch when the toggle Switch is turned on and off (starting up and shutting down the pc) ("Please note this is momentary, on/off will not work") otherwise i would use 4pst switch.
epicfatigue said:My other Question is there an IC out there that can do the job of the switching eliminating the need for so many relays?
from the datasheet said:The MC14551B is a digitally−controlled analog switch. This device
implements a 4PDT solid state switch with low ON impedance and
very low OFF Leakage current. Control of analog signals up to the
complete supply voltage range [18v] can be achieved.
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