Do it yourself circuit.. I built the timer and it works perfectly. I would recommend that this only be tried by a person familiar with electronics !!

Not to belittle your work, cause what you have would probably work, but the car's electrical environment is WAY too dangerous to have a 555 timer hooked up like that. Your chip you have has a max input voltage of 15 volts. Some have 16 or 20. But I have personally seen circuits with a max input voltage of 30 v literally explode inside cars due to the transients that are on those lines. I have also seen circuits with a max of 20v survive forever. So, just be careful. I wouldn't put that in my car the way it is. Just my own experiance talking.

I understand your concerns about the dangers of transient voltage spikes
on the AUX line. Normally, a good car battery will surpress all but a fraction of the spikes if a good heavy ground is used.
I will add a 14.5 volts zener and possibly a Transient suppresser to the circuit. This way, the circuit would be safe in-case the car battery goes bad. It would basicly duplicate the 555 circuit power on the infomation center which came as a factory option (display Clk). The 555 timer I'm using has a nominal value of 14.5 Volts and is spec'd from 12.5 to 20 Vdc.

Electronic experiance is needed, the wrong manufacturer of the 555 timer
can result in problems. Please research the components used and watch
the ratings!!!

Cliff

You are right, normally a car battery will get rid of all but a fraction of voltage spikes, but it only takes 1 to blow out a circuit.

You might want to make the zener a little higher. It's not uncommon for some alternators and regulators to run close to that normally.

Something else I learned, that some portable battery jump start packs run at 24V's. So just incase anyone will ever use one of those, you will want to make sure this circuit can run off 24V just incase. That was a surprise to me.

There are all sorts of voltage spikes.... from the fan motor and others. Some experts say to expect 80V on the +12V wires on a car, even with a good battery. Depends on who you listen to of course.

So yes, heed his warnings and just be careful making and spec-ing out parts for something like this. Or of this is getting too complicated you can just buy one of my circuits (I have already taken care of all that stuff). :)

www.sminntech.com/products.html

I thought this is a opened forum. Why kill the circuit attached ??????

Whatup ? said:

I thought this is a opened forum. Why kill the circuit attached ??????

Why kill the circuit? Who is killing it? Me? I didn't kill anything.
If I wanted to kill it, I'm a mod I would have deleted the post and banned the user.

I was just warning people because that circuit works on the bench,
but if you put it in a vehicle you could end up with actual exploded parts,
I have personally seen it. And you can too below if you sign in and can see pics.

The average 555 timer is a 15 volt part, that's way too close to a car's
electrical system for my taste. Here is a picture of a 30V part. A car
has a 12V system. The pic below has over 200% of room over 12V for
safe operation. And in a new car with a brand new battery... well...
You can see what happens.

This was a picture taken by a friend of mine to impress
upon me why I should be careful with my circuits that I sell. This was in a
BRAND NEW car. What can happen with electronic circuits if you are not
careful and then install them in a car. Hell, even the poster's 20V 555 is
too low in my experiance.

I just don't want someone to build one of these, as is, and have
something blow up on them. We try to watch out for eachother here.

Whatup ? said:

I thought this is a opened forum. Why kill the circuit attached ??????

He can't see it because he's a guest.

"Whatup", If you read about the forum, GUESTS CAN NOT VIEW ATTATCHMENTS.

JasonH said:

Whatup ? said:

I thought this is a opened forum. Why kill the circuit attached ??????

He can't see it because he's a guest.

"Whatup", If you read about the forum, GUESTS CAN NOT VIEW ATTATCHMENTS.

I thought he meant that I was trying to "dis" cliffp's circuit and say
nasty things about it. I never thought that he couldn't see the
attachment and thought we (either you or I) removed it or something.

Oh well, cool pic of the blown part though huh?

So if anyone wants to make car electronics, take it from someone who knows,
make sure you know what you are doing (which cliffp said before I did). It's good advice.

instead of a zener could one not also consider putting a decent regulator circuit and filter to supply the 555 circuit? perhaps regulate the whole thing down to +5 volts and use a lower voltage (maybe 6V) relay... or perhaps consider using MOS or transistor based switches in place of the relay..

just a thought...

cliffp....would you please edit and resize your circuit so we con't have to chase this thread all over our screens?

03Aviator said:

cliffp....would you please edit and resize your circuit so we con't have to chase this thread all over our screens?

I don't know if he can, bit I can (I forgot I was a mod here). :) I didn't think of doing that. How about now. I shrunk the pic and included one in a zip file of the original size.

Just remember to add some high voltage protection to this circuit before building and installing into a vehicle.

ducatiboy said:

03Aviator said:

cliffp....would you please edit and resize your circuit so we con't have to chase this thread all over our screens?

I don't know if he can, bit I can (I forgot I was a mod here). :) I didn't think of doing that. How about now. I shrunk the pic and included one in a zip file of the original size.

Just remember to add some high voltage protection to this circuit before building and installing into a vehicle.

Perfect! Thanks Steve!

ducatiboy said:

You are right, normally a car battery will get rid of all but a fraction of voltage spikes, but it only takes 1 to blow out a circuit.

You might want to make the zener a little higher. It's not uncommon for some alternators and regulators to run close to that normally.

Something else I learned, that some portable battery jump start packs run at 24V's. So just incase anyone will ever use one of those, you will want to make sure this circuit can run off 24V just incase. That was a surprise to me.

There are all sorts of voltage spikes.... from the fan motor and others. Some experts say to expect 80V on the +12V wires on a car, even with a good battery. Depends on who you listen to of course.

So yes, heed his warnings and just be careful making and spec-ing out parts for something like this. Or of this is getting too complicated you can just buy one of my circuits (I have already taken care of all that stuff). :)

www.sminntech.com/products.html

Hmmm.... What I find to be quite interresting is the fact that neither my MECP, or series of ASE tests ever included information on anything you have mentioned above. In addition, how exactly in my field have I never come across this problems myself? I have incorporated 555's in the past for timed triggering of window roll-up/down, autolights, vacuum locks, ect. As long as a simple power supply was placed in front of the circuit (a simple v-reg with proper capacitive dampening), any deviation was of no concern.

Lastly, there is a reason for diode suppresion of any electromagnetic device in a vehicle (relays, motors, actuators)... this is to avoid the issues that you have listed above. In the end, your dampening save all is your battery. Any malfunctioning, or poorly designed suppression system would sooner destroy the fragile electronics already aboard a vehicle if a problem were to happen with a properly regulated 555 circuit. (edit: make note of relays labeled "diode suppressed" or diodes in your fuse box incorporated into motor circuits)

However... I will agree with you on the fact that this circuit as it stands is a terrible idea with its lack of regulation. I think, for the very reasonable price you offer, your kit is well suited for those who are unsure with what they are doing. It's experiments like this that damage perfectly good (and expensive) equipment... on top of a potential fire hazard.