5 minute Time delay

[bryan1]

Hiya Guy's,
Well I finally got some time to tinker with my electronics( da missus ain't home) and I got my 3 watt led setup as a night light for when I walk back to the house. This led is shining a path around 30 metres which is great but ideally I want to set up a 5 minute time delay so it switch's off automatically. My first thought was using a 555 but with that type of delay I'd need a bigger cap than is recommended. I did see a few years ago a work around for longer time delays but after searching I keep coming up with blanks. I could use a pic but thats overkill so does anyone have any reference to using long delays with the 555?

Cheers Bryan

 

[Nigel Goodwin]

Hiya Guy's,
Well I finally got some time to tinker with my electronics( da missus ain't home) and I got my 3 watt led setup as a night light for when I walk back to the house. This led is shining a path around 30 metres which is great but ideally I want to set up a 5 minute time delay so it switch's off automatically. My first thought was using a 555 but with that type of delay I'd need a bigger cap than is recommended. I did see a few years ago a work around for longer time delays but after searching I keep coming up with blanks. I could use a pic but thats overkill so does anyone have any reference to using long delays with the 555?

A PIC isn't 'overkill' it's a simple solution to the problem - an 8 pin PIC is the same size as a 555, and requires far less support components. It will also far out perform a 555, and can replace it in many circuits (but obviously not pin for pin!).

 

[bryan1]

Hiya Nigel,
I suppose your right there and I do have a few 12f675's around and I am in the process of making up a pic based rpm meter so it won't be hard to write up some code and use the pic.I just thought for a simple circuit that I need, a one shot 555 would be the easiest.

Cheers Bryan

 

[runningl]

Example on AVR here:
" Long Delay Generation Using the AVR Microcontroller "
https://www.electro-tech-online.com/custompdfs/2006/02/doc1268.pdf

 

[JimB]

If you can find one, a ZN1034 IC will do just what you want.
It is a long delay timer, made by Ferranti, (now defunct).

It contains the circuit for an RC oscillator followed by a divider circuit. So the oscillator can run at a relatively high frequency, but the output delay can be hours or days etc.

Just had a separate thought, you could use a 555 as an oscillator follewed by a 4040 12 bit counter to give a long delay.

JimB

 

[chemelec]

A CD4541 can be programmed to time seconds to HOURS.
5 Minutes, No Problem.
Probably quicke to make than programming a pic.