More Electronic Circuitry help: Electronic Timer

[Fri]

Guys, I need your electronical expertise help once more. Could you guys help me in finding a way/circuitry diagram for a kind of timer?

I need a simple way to turn my current project off automatically after about thirty minutes. I'm currently trying to find it as well, but everything that I found are kinda too complex. I thought, what I want the timer to do is quite simple! Are there really no way to do that in an easy way?

[Keld Denar]

This might help...

http://imgs.xkcd.com/comics/circuit_diagram.png

[Archonic Energy]

buy a timer switch which sits between the mains and your project.

Done.
:smalltongue:

[BisectedBrioche]

How complex a circuit do you want? If you want an accurate timer your best bet would probably involve an IC.

What you need to do is basically use a capaciter (since it'll charge/discharge at a predictable rate with a constant current) as a pacer and your best bet is a standard 555 Timer IC.

Just google something like "555 timer circuit". They might look a little intimidating at first, but when you understand how they work it'll be easy.

EDIT: It might help if you give more details of what your project is and what you're trying to do, BTW. Particularly what voltage you want to run it at.

[Fri]

thanks. I'm a product design student that's currently working on some kind of power-nap machine using white noise. Power nap only work if we wake up before the deep sleep kicked in, that is about thirty minutes after we start to doze.

I already got the way to generate the white noise, it's quite simple and works with a nine volt battery, which make it quite portable. What I need now is a way so the generator will automatically shut down and kick a buzzer on to wake the user after thirty minutes.

so... I guess that means I need a timer that work with 9 volt DC power supply, and small (simple) enough to be worn on the head...

[BisectedBrioche]

thanks. I'm a product design student that's currently working on some kind of power-nap machine using white noise. Power nap only work if we wake up before the deep sleep kicked in, that is about thirty minutes after we start to doze.

I already got the way to generate the white noise, it's quite simple and works with a nine volt battery, which make it quite portable. What I need now is a way so the generator will automatically shut down and kick a buzzer on to wake the user after thirty minutes.

so... I guess that means I need a timer that work with 9 volt DC power supply, and small (simple) enough to be worn on the head...

Yep, you definatly want to use a 555 timer based circuit. Do you have much experience with soldering/electronics?

The alternative would be using actual clocks, but presumably you don't need exactly 30 minutes?

This page has the info you need, more or less: http://wiki.answers.com/Q/How_do_you_build_a_simple_timer_circuit

[Fri]

Hm... no more suggestion or nudge? I guess I'll restart my search with the afromentioned circuit as the base then.

[Archonic Energy]

Hm... no more suggestion or nudge? I guess I'll restart my search with the afromentioned circuit as the base then.
http://en.wikipedia.org/wiki/555_timer_IC

Vin = 3-15v
voltage used 9v
in tolerance
T=1800 (sec)

T= R C

using commonly available values for R & C
C= 1000 uF = 0.001F +/-20%
R= 1M8 Ohm = 1,800,000 ohm +/-1%
C x R = 1800.

Done.
see if you can find more accurate capacitors.

[BisectedBrioche]

Hm... no more suggestion or nudge? I guess I'll restart my search with the afromentioned circuit as the base then.

All you really need to do is adjust that circuit to 30 minutes (I'd suggest finding the highest value capacitor you can run off 9v and then selecting a resistor to adjust the value accordingly).

Then you can just connect the output (3) pin to the base of a transistor (PNP, so the current is stopped when there's a current at the base) and wire the collector and emitter of the transistor into the rest of the circuit (you might need a resistor to lower the output voltage of the pin).

This program might be useful for building your circuit: http://my.ece.ucsb.edu/bobsclass/2C/Simulation/circuit_maker.htm

BTW, if you want to avoid all of this you could always cannibalise a cheap electronic alarm clock...

[Fri]

All you really need to do is adjust that circuit to 30 minutes (I'd suggest finding the highest value capacitor you can run off 9v and then selecting a resistor to adjust the value accordingly).

Then you can just connect the output (3) pin to the base of a transistor (PNP, so the current is stopped when there's a current at the base) and wire the collector and emitter of the transistor into the rest of the circuit (you might need a resistor to lower the output voltage of the pin).

This program might be useful for building your circuit: http://my.ece.ucsb.edu/bobsclass/2C/Simulation/circuit_maker.htm

BTW, if you want to avoid all of this you could always cannibalise a cheap electronic alarm clock...

Thanks. that kinda make sense and understandable. And believe me, I'd cannibalize an alarm clock if I know what to do with it.

[DSCrankshaw]

Hmm, a 30 minute cycle is kind of long for a 555. I'd probably use a shorter cycle time and combine it with a counter. Or just find a timer IC that you can program for the proper time.