DarkSlkayer said:
Hi I was wondering if someone knew how to make one of these
A monostable circuit to simulate a press of the reset button for a second when the circuit first receives power.
A diagram would be helpful
Thanks
I think you could accomplish this with a capacitor and a resistor. I don't feel like uploading pictures at the moment, so I'll try to describe it using node labels.
Let's call our nodes Vs, V1, V2, and GND. Vs will be our voltage source, V1 will be the node that would expect to get power when the switch is active, V2 will be the node that would expect a voltage from the reset button (I assuming it's active-high, but if it's active-low we'll have to re-think), and I think GND speaks for itself.
Your button will be connected between nodes Vs and V1. Your Capacitor will be connected between nodes V1 and V2. Your Resistor will be connected between nodes V2 and GND.
Why would this circuit work? A capacitor charges as it is fed a DC voltage. As it reaches it's final voltage, it allows less and less current through until it reaches that voltage and acts as an open circuit. Because of this property, it filters out DC signals that are applied for a long time (very relative term). AC signals, on the other hand will pass right on through the capacitor. How does this help? Changing the state of the button changes the voltage on the capacitor, making it act as a short-circuit in the moments immediately proceeding the changing of voltage, allowing a pulse to get through before it settles on it's new voltage and acts as an open-circuit again.
The resistor is used to set V2 to low while the capacitor is acting as an open circuit, but when it becomes a short-circuit during that pulse, the resistor prevents Vs from shorting all the way to ground but rather goes into the RST pin. If the resistor were not there, when the capacitor acted as a short circuit, it'd go straight to ground, bypassing the RST circuit, since ground would be the path of no resistance.
Of course, this is all theoretical, and I don't have any particular values for you to use.
