Looking for Help with a Long Delay, Low-Powered Timer Circuit/Device?

Question

I have an application where I want to start a toy fan after a (roughly) "tunable" time delay.

For example, I might press a "RESET" button and the delay will start... and after maybe 6 to 8 hours, I want to switch-on the fan.

Now, for smaller delay times (in the order of seconds or a few minutes), I could use a simple 555 timer monostable circuit... but obviously, I need significant longer delay times than that.

I'm looking for a design or device that I could use that would provide delay times of 6-10 hours. The switching capacity is not huge (turning on a small, 1.5V, say, electric motor), so I don't think I need to consider relays, etc... and I want to be able to power the unit by, say, a 9V "brick" battery or maybe even 2 or 3 Lithium/button batteries.

(...had a thought as I was writing...)

Perhaps I could incorporate a 'decade counter' or something...(!) So, let's say I have a monostable 555 design that delays for 3 minutes... I would need a counter device to maybe count to [ (8 x 60) / 3 ] or 160... and when the relevant output went 'high', maybe that could turn 'on' a transistor or something... until I press the reset button and it would all start again.

Hmm...

...or maybe I can just buy a digital clock/watch module and hook-up an alarm output to the switch!?

Anyway, I would greatly appreciate any thoughts or suggestions... Thanks!

Answer 1

CMOS 555, tantalum timing capacitor.

There are other chips which can be used for long duration timers, such as the 4060, which can generate a more accurate delay

Answer 2

Use a small micrcontroller (like one from the PIC12 series).



But: if the motor needs 1.5 volts, why would you want to power the setup from 9 Volts? Output current for these micros is limted, though - usually 20 mA tops - so you might need to consider a driver stage (low voltage MOSFET or such).



Depending on the supply power you want to go for, you'd need the PIC, possibly the driver, the button and the battery. Oscillators and such are built into the PIC. If you want to use a power supply greater than 5 Volts, there are also some PIC12's with a built-in shunt rgulator, in which case you'd have to add a shunt resistor to the list.

Answer 3

You could buy a countdown timer, and use the alarm output to trigger a transistor on. The piezo alarm output might be connected to a bridge rectifier ac (needs a fast rectifier) inputs, with the dc output feeding a capacitor and base of a transistor.



A cheaper way might be to use the Arduino Pro Mini, ($2.50) along with a slightly modified example sketch called BlinkWithoutDelay. The Arduino can easily count the milliseconds as soon as it starts up, and compare with a given number of milliseconds equal to, say, 7 hours (25,200,000 milliseconds).

Answer 4

Yes go for a CMOS 555 and a couple of CMOS counters if you want to use discrete components. If youre prepared to invest in a programmer and write the software a PIC would be by far the best choice.

Answer 5

using PIC programmable IC u can set the timer from 1-99 minutes,

5v to 9volts power supply needed to active this,