Re: 1 second pulse
ljcox said:
I don't think you answered Ron's question.
What initiates the pulse? Do you want it to start when power is applied to the unit or after you press a button?
Yes. As soon as the circuit is powered up, the pulse would go high [or low] for one second, then stay low[or high].
It doesn't matter whether or not the pulse is high or low, I can adjust the connections to the relay accordingly. There is no push button in the circuit.
The circuit is powered by an appliance timer that turns on at 8:30 am every morning.(sounds crude, but its the simplest ($4.00) way short of building an appliance timer myself) The appliance timer turns off 5 minutes later since the circuit already did what it needed to do.
(just like myself physically going to the PC and holding in the momentary on/off switch for 1 second)
The relay just briefly joins two pins on the motherboard, that powers up the PC.
At night, the PC is shut down automatically by software. The next day, the circuit is powered up at 8:30 am, and the PC is turned on again.
ljcox said:
The 555 circuit you posted only gives a short pulse after the button is pressed. But you wrote that you want the pulse to go high and remain high after about 1 second. So what starts the 1 s timer?
The capacitor and resistor value in the circuit I posted needs to be changed to 100uF and 10K. This will give a one second pulse.
Ron H said:
Evidently you can't just use the switch. Is that because it is actuated by something that doesn't allow it to be closed for the required amount of time?
Yes the PC is powered up by a momentary push switch. This switch simply joins two wires together on the motherboard for as long as the human holds in the switch, the momentary switch must be closed, then open. The time that the switch needs to be closed is not important. A human would press the switch for under 1 second, so that is the reason for the 1 second pulse. (give or take 0.3 seconds)
I hope I answered most of your questions.
Remember: I have this working PERFECTLY with a microcontroller.
Out of shear curiosity, I would like to know of a REALLY simple way (least amount of components without the microcontroller) to make this work.
I have seen simple reset circuits for the 8051 microcontroller that delay the time period while the reset is low. A simple resistor and a capacitor. I was thinking that this type of setup could somehow be modified to work with what I am doing.
I included a basic schematic (please forgive me, I'm NEW)
Cheers