# Building a device that turns on for 3 seconds every minute. Need help!

#### Vassende

Joined Mar 31, 2016
5
Hi!
I don't know wer to begin so I'm hoping you could help.

I need a circut that will, once powered, deliver current for 3 seconds every 60 seconds.

The output current will control a relay that will give power to a pump, but that is a different story. It will be used in a car.

The circut is best if it runs on 12v or 5v since they are the easiest to find in a car.

I was looking at a 555 timer but with very little knowledge on small electronics, I don't know were to begin.

The smaller, more simple, the better.

Could some of you help me? Parts etc.

Thank you!

#### TheButtonThief

Joined Feb 26, 2011
237
A 555 is the direction in which most people here would point you in, as it's pretty much the most simple and cost effective solution to small timing tasks. Alternatively, a micro controller.

Some things to consider though, does it need to be 3.00 seconds and 60.00 seconds or is 3.05s and 60.10 acceptable? Does the 60 second period begin when the 3 second period has expired or is the beginning of the 3 second period 57 seconds from the end of the last one? What sort of current are you switching and at what voltage? Are you ok using discrete components or are you looking for a modular approach? Do you have a budget?

Personally, I'd use a micro (like an ATtiny85) with a MOSFET but I already have loads lying round and the capability to throw a program together that would do the job in just a few minutes.

#### Vassende

Joined Mar 31, 2016
5
The timing is not really important.
I need the circut on trackdays to power a waterpump that sprays water onto the radiator. I've found that around 3 seconds of waterspray every minute or so does the trick.

I'm flexible on components, price etc, but I need it to be simple for me without any special knowledge to build.

I need a output between 5v and12v so I can give signal to a normal auxiliary relay (the type you would use on aux lights on a car etc). The relay will then handle the higher amps etc.

#### Dodgydave

Joined Jun 22, 2012
9,206
A 555 hysterical astable will do it easy, two presets set each time individually.

#### dannyf

Joined Sep 13, 2015
2,197
There are lots of timers that will do that. My recommendation is a mcu - simple programming.

#### Marcus2012

Joined Feb 22, 2015
383
I think "simple programming" is an oxymoron depending on your perspective. I second DD and buttonthiefs 555 suggestion, it seems the simplest thing to understand from a non-electronics background.

#### blocco a spirale

Joined Jun 18, 2008
1,546
+1 for the 555

For someone who doesn't know where to begin and for a non-critical timing application, a 555 is the obvious choice. It's difficult to see the benefit of a micro-controller, all things considered.

#### Vassende

Joined Mar 31, 2016
5
Thanks!

I thought a 555 timer would give me just the "burst" of current when triggered? How do I get a set amount of time, after a set amount of period?
Ex. 3 seconds every 60 seconds.

#### Dodgydave

Joined Jun 22, 2012
9,206
Here's a circuit diagram with adjustable separate times...

#### GopherT

Joined Nov 23, 2012
8,012
The timing is not really important.
I need the circut on trackdays to power a waterpump that sprays water onto the radiator. I've found that around 3 seconds of waterspray every minute or so does the trick.

I'm flexible on components, price etc, but I need it to be simple for me without any special knowledge to build.

I need a output between 5v and12v so I can give signal to a normal auxiliary relay (the type you would use on aux lights on a car etc). The relay will then handle the higher amps etc.
This is easy as it gets

#### Vassende

Joined Mar 31, 2016
5
Here's a circuit diagram with adjustable separate times...

View attachment 103476
If I understand this right:
You use one potentiometer to control the time between, and one to controm the lenght of the burst?
I have no parts around, but I recond I could find all the parts online? Ebay etc?

#### crutschow

Joined Mar 14, 2008
25,121
There are lots of timers that will do that. My recommendation is a mcu - simple programming.
To you perhaps, but not generally for someone with "very little knowledge on small electronics". There's nothing "simple" about programming to a person who's never done programming.

Below is a single 555 circuit that should do the job.
R1 controls the relay ON time and R3 controls the OFF time. They can both be pots, if you want some adjustment.
The parts can be purchased at any online vendor such as Digikey, Mouser, Farnell, inc.
I would avoid ebay, because of the chance of bad knockoff parts.

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#### Dodgydave

Joined Jun 22, 2012
9,206
Yes each pot controls its own time, so the 1meg pot controls the 60seconds, and the 100k pot controls the 6 seconds.

#### Vassende

Joined Mar 31, 2016
5
My day just got a whole lot of better!

I love smart people. Makes me want to learn.

I'll order some parts from around the web since they are not possible to buy in my country.

Hopefully I'll get something that works and not a whole lot of magic white smoke.

#### Colin55

Joined Aug 27, 2015
519
Oh. I wired it incorrectly !!!!!

Last edited:

#### GopherT

Joined Nov 23, 2012
8,012
Thankyou Crutschow. I have just blown up my transistor.
let me try that again.
Why did you blow up your transistor? The 1k should be a fine to limit current to the base. No current will be supplied by the DIS pin, what else could you have done wrong that caused your poor 2N2222 to "blow up"?

#### dannyf

Joined Sep 13, 2015
2,197
deliver current for 3 seconds every 60 seconds.
that's a duty cycle of 5% - not impossible but doable in a 555. You will need to produce a period of 60 seconds and then reduce the duty cycle to 5 seconds - in a 555 timer, the two are somewhat related.

A better approach might be a relaxation oscillator.

#### Bordodynov

Joined May 20, 2015
2,627
See

#### dannyf

Joined Sep 13, 2015
2,197
Or a mcu: I wrote this for another discussion where they needed a 6 seconds on for every hour. Changed it to 3 seconds / 1 minute.

Code:
#define SW_DURATION        (3sec)                //sw on for 6 seconds
#define SW_PERIOD        (1min)                //every /*1hr+30min+*/20 seconds
it recompiled to ~200 bytes.

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