Power On Timer 2

[jasonOSU]

I have searched the internet for hours and been unable to locate a simple power on timer. I would like to activate the circuit, have it count for 3 seconds, then power on a motor or solenoid. I am running 9 volts DC. I have found many explanations on using a 555 but those circuits are on for x seconds then off. I need off for 3 seconds then on until I kill the circuit. I would like to minimize my components of course by avoiding using an inverter. I know there must be a simple RC circuit for doing this.

 

[buzzp]

There are many ways to make it but for an off the shelf solution you need a delay on make timer. These are sold by almost everyone under the sun and should be available for less than $20 US. A couple of companies I can think of (not necessarily recommend) are SSAC or Time Mark. Search for delay on make and youll find many more.

 

[nbucska]

You can use a 4000 series CMOS singleshot and use its Q-NOT
output.


<nbucska@pcperipherals.com>

 

[OperaHouse]

If you want something nicer, search for MC14541. This CMOS chip will operate on that voltage and is quite repeatable. Operates in ON DELAY and other modes, fractios of a second to hours and will drive a transistor.

 

[blcpro]

You could use an RC circuit to bias an NPN transistor to engage a relay. Or if your current demands are low, then perhaps only the transistor is required.... the delay can be set by various combinations of Resistance and Capacitance. Once the circuit is powered, the capacitor can charge up to your 9V through the resistor. When the voltage across the capacitor goes above the threshold for the transistor, the circuit will remain ON.