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I would use either a monstable 555 set for the time you wanted, or you could use an astable 555 using a counter such as the 4017 as a clock divider, with the ignition circuit connected to an appropriate pin on the counter for the amount of time you need.
If all you need to do is switch 9-18v to ignite the rocket, I would use a relay, mosfet, or transistor connected to the output to your timing circuit.
do you just want a circuit that gives you a delay between the time you turn it on and the time it launches the rocket?
so you want to do it just with no indication? or you want some way to show how much time is left till launch?
you could use, like mattg2k4 said, a 4017 and connect a led with a series resistor to Q0-Q8 and have Q9 for launch. this way you have an indication of about how much time you got till launch. or you can make a more complicated circuti wich will display the time left on some 6 segment displays.
No I want it to be easy and cheap. And yeah I want a circuit that gives you a delay between the time you turn it on and the time it launches the rocket. But it would have been nice if a led was turn on about 5 sek before the lunch or some thing.
Here's one that drops a 6 volt load after a certain amount of time, which you can calculate how much you want it to delay by factoring resistance and capacitance.
I know it's not exactly what you want, but you can always use a step up transformer or a more powerful relay to get the 9-12 volts you need.
Also it has no LED in the circuit itself, but you could put one before the relay so it will light up when the load is being delivered, which with 6v will take about 3-4 seconds to ignite an estes model rocket engine.
You could also place an LED after the switch so you know when it's active, and make it green for go, and red for the ignitor LED so you know when it's hot.
how about using a circuit like this.
first, apologise that i don't have time to draw the schematic now, i will draw it as soon as i have time, or maybe someone has time to do that.
use a 555 timer to generate about 1Hz with it. connect the output to a 4017 decad counter. use a transistor and relay connected to Q9 wich will trigger the rocket. then for the other outputs you can connect some leds. this will give you indication on how much time it is left. you could use different colour leds, use the first 3 red, next 3 yellow, and last 3 green. this way the leds will turn on in order.
you will have like this: RED, RED, RED, YELLOW, YELLOW, YELLOW, GREEN, GREEN, GREEN, LUANCH!!!!
or you can use less leds to know how much time there is left.
i'll be back soon with some schematic.
also, what will be used to launch the rochet ? is it a resisance that will heat up and turn on the engine? how much current will it draw?
also, another mechanism must be used to turn off the launching circuit after the launch takes place.
i would also use a beeper, or buzzer connected to the output of the 555 to have an acustic indication on the process.
anyway, here is the schematic of what i am talking.....
well, you have 9 leds wich show you how much time you got.
you could unse only the last 3 leds, to indicate the last 3 seconds before the launch....
the timer is set to about 1 second for each led, so you have 10 seconds before ignition.
well, it is neither easy, nor cheap. the full program costs a few 1000's , but the light edition is free.....
you can get the cd from here
hope it helps you. i know i ordered it twice before i received it. the first time i received a phone call so that they could confirm the order, and i didn't get the cd......the second time i got no phone call, but i got the cd..