12 v. repeat time delay relay off first help needed

[doublebogey]

I need the above to control a switch. (just close a circuit, no voltage) My input will be 12v cigarette lighter or equivalent. I cannot build a board. I have no knowledge to accomplish that. Does anyone know of an off the shelf relay that would do this for me. The time delay is not that important but must be under 3 minutes max. I appreciate this help like you wouldn't believe. Once again 12v. input repeat off first. Output just continuity. Thanks

 

[CocaCola]

After reading that three times I'm still not sure what you want...

I get that you want a relay to turn on and off but beyond that I'm lost...

Do a timeline like this if you can't put it to words...

Off - 2 minutes
On - 3 minutes
Off - 1 minute
On - 1 minute
repeat

Also clarify this "(just close a circuit, no voltage)" the circuit it's opening/closing has to have a voltage and current or else it's not going to accomplish anything...

 

[doublebogey]

clarification

Thanks Coke. To be exact. This application is in a tractor. I cannot modify it. It is not mine. The tractor by computer shuts off after about 3 minutes. I don't want it to shut off. It has a reset button which is manually pushed and resets the timer. I want a repeat timer that will accomplish the resetting without manually pushing the reset button. I thought if I could tap on to the reset button leads with the output of the relay which I mentioned , I could accomplish the same thing as my finger resetting the button. I hope this clarifies what I need. And thanks for the help.

 

[CocaCola]

I take it this is bypass an inactivity or at least test for an alert operator safety...

An Astable Multivibrator made with a 555 timer would do the job, just set the pulse to about every 2 minutes or so...

As for you stating you can't do it yourself, I suspect you can do it yourself you just need to apply yourself... The 555 timer is an easy chip to work with and for this circuit it will only require a few external components... A small reed relay won't require that much current and can be driven directly from the 555 output to do the tapping that is likely a very low current...

This could but built on the stab lock prototype boards or even better get a cheap soldering iron and try soldering it up, it's a good skill to learn...

 

[MrEE]

How about permanently bypassing that reset button, in other words just connect a wire across the two button terminals. This effectively keeps it reset. I am not sure though if the tractor' s computer likes that or not, but it won't hurt to try.

 

[CocaCola]

How about permanently bypassing that reset button, in other words just connect a wire across the two button terminals. This effectively keeps it reset. I am not sure though if the tractor' s computer likes that or not, but it won't hurt to try.

Good point, probably would have been my first test if I was doing it to something I owned... I would hope that if it's a legit safety feature that the computer wouldn't be fooled by a constant short, but it wouldn't surprise me in the least if it was that easy to bypass...

 

[doublebogey]

Bypassing the switch is an awesome idea...BUT...the computer has to sense an input, else shutdown occurs anyway. Coke...I am going to research your idea. My neighbor is a PHD electronics, and introduced me to the 555 a few years ago when I last tackled this endeavor. He too thought this was an easy thing with the 555 but gave up on it. I am not saying it's hard. He was rusty and I know nothing. This leads me to want an off the shelf timer. Thanks guys. Any other ideas are appreciated while I do my Coke research.

 

[doublebogey]

The purpose of the reset switch is not a safety concern. It is to save fuel on an unattended tractor. Thanks

 

[CocaCola]

Bypassing the switch is an awesome idea...BUT...the computer has to sense an input,

Shorting the switch is the same as pressing it constantly... Unless the computer is actually watching it for a swing from open to close and back it will work... Depends on how they wrote the detection script...

He too thought this was an easy thing with the 555 but gave up on it.

To be blunt he didn't try too hard, the circuit is only a few components... There are 1001 examples of it in a Google search, the only thing you will need to adjust is the duration and there are calculators for that, heck you don't even need to get that close in this application you could probably wing the calculations and get close enough... From that point you would hook up the relay from the 555 output and vcc with the other two legs across the switch... I suggested a reed relay because they a cheap and require very little current to activate, and if you are in the US Radio Shack actually carries them in the store...

http://www.radioshack.com/product/index.jsp?productId=2062479

The 555 timer will also operate at the 12V so you can hook this right to the cigarette lighter supply simplifying the circuit even further...

http://freespace.virgin.net/matt.waite/resource/handy/pinouts/555/

Pull down to the astable calculator... I plugged in a few over the counter Radio Shack values, there are easier ways to do it but this worked just using what I know Radio Shack has in stores...

***** Edit see revised post a few down...

 

[MrEE]

Of course the 555 solution is exactly what you asked for. This can also be built with two transistors configured as an astable oscillator. There is plenty of info online on both solutions.
Here is another idea: put some sort of a sensor that tells when a driver is sitting. As long as there is a driver sitting, the reset is active otherwise the computer times out after 3 mins.
I don't know of any off the shelf timer. Check the big online auction site. If this is an item of high demand, perhaps I can have it manufactured.

 

[doublebogey]

The driver sitting is an idea...BUT...that would be constant. The computer won't accept anything other than an intermittent input. Then it resets for the 3 or so idle minutes.

 

[CocaCola]

BTW, ignore my resistor cap values in the last post, I was slightly distracted by children at the time, and was thinking seconds not minutes, they need to be adjusted for mintues...

 

[doublebogey]

Somebody build me one that works for my application and I will buy it. If it works, I know of others that may be interested.

 

[CocaCola]

Here is a more to job version using two 1M resistors, 10K resistors and a 100uf capacitor... Again all Rat Shack over the counter values...

Note this is logic 'low' when you want it active, so you should connect the relay between +vcc and the 555 output, when it goes low it will trigger...

 

[CocaCola]

Somebody build me one that works for my application and I will buy it. If it works, I know of others that may be interested.

If you insist, drop me a PM and I can build it for you from one on a prototype board to a professional run of them...

 

[MrEE]

then have the driver jump up and down every 2 minutes .. but seriously though, a seat sensor and a 555 together will be as automatic as can be. The seat sensor enables the 555 circuit when a driver is present.

 

[doublebogey]

True, I now see what you mean. That however for other reasons is not appropriate for what I need. Heh. Coke... this forum will not allow me to PM you. I am new and have not had the required 15 posts. can you e-mail me and I will respond that way. Thanks steve_nancy86@hot...... you know what.

 

[CocaCola]

doublebogey I sent you an email, let me know if you received it, if not I will setup a temporary email address for you to email me at...

Edit, actually to make it easier I have setup a semi-permanent email for this forum... I won't check it unless I'm expecting an email (this will allow me to bulk nuke the spam) this semi-permanent email will save me the hassle of creating a new temp email all the time... You can contact me at coca-cola (at) hushmail.me

 

[doublebogey]

Thanks Coca Cola. I did get it and I e-mailed you.

 

[CocaCola]

I will touch bases with you later today when I have more time to compose an email...