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new to circuits first real project

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jjanes

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This is a newbie question and I hope not too dumb

How do you start??

I have a project in mind

I know voltages and amps of the different aspects I want to control but where do I begin

I want to build a circuit that will prevent my car headlights from being on unless my ignition switch is in the ON or ACCS position.

I have attached a circuit design but need help with components and verificatiion that it will work it is very simple or so I think:D

Is there a better way??

Thanks for your time in answering this newbie question


Oops forgot
when point 1 is live then the switch at point 2 closes, closing that circuit and the headlights are on if the main headlight switch is on

when point 1 is dead then the switch at point 2 remains open and that circuit is open even if the main headlight switch is on
 

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hi,:)

I would suggest a better more common way regarding headlights and ignition.

When the ignition is switched off with the headlights on a loud buzzer sounds.
This is what my car does, works quite well. No power relays involved.
 
I do understand about the buzzer but I want to learn about electronics and the best way for me to do that is by trying to get something built that I do not know how to do but am able (with help) figure it out.

Thanks for your post but I would like to really try this out
Jeff
 
I do understand about the buzzer but I want to learn about electronics and the best way for me to do that is by trying to get something built that I do not know how to do but am able (with help) figure it out.

Thanks for your post but I would like to really try this out
Jeff

Understood.

Are the car headlights controlled by a relay or directly from the headlight on/off select switch.?
 
hi,:)

When the ignition is switched off with the headlights on a loud buzzer sounds.
This is what my car does, works quite well. No power relays involved.

Hi Eric,

buzzers certainly have an advantage, sometimes not:

A pilot comrad of mine landed his plane with the landing gear up. After the crashlanding (Oops, going further down, I didn't expect that. :) ) he was asked why he didn't go around as advised by the tower personnel. He replied: "The warning horn was so loud. I didn't understand a word." :D

Hans
 
It is a 1973 Mustang Convertible I believe it is directly from the switch most things were mechanical back then so that is my assumption it very little in the way of electronic devices and being Ford if it could be done with a switch it probably was.

...in my task of trying to learn something here let me guess at your thinking if it were a relay I coud swap the driving leading(not sure of the nameing convention) but the wire that tells the relay to activate is the one I mean, but I could make the connection come from the ignition switch being in the ON position. Was that your thinking??
 
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It is a 1973 Mustang Convertible I believe it is directly from the switch most things were mechanical back then so that is my assumption it very little in the way of electronic devices and being Ford if it could be done with a switch it probably was.

...in my task of trying to learn something here let me guess at your thinking if it were a relay I coud swap the driving leading(not sure of the nameing convention) but the wire that tells the relay to activate is the one I mean, but I could make the connection come from the ignition switch being in the ON position. Was that your thinking??

hi,
The wattage of the headlights is quite high, assume 60Watts/lamp, thats 10Amps total.
So a relay or power transistor/MOSFET would be required to switch the lamps.

Personally I would choose a relay, you will also require a circuit to sense the state of the ignition switch and headlights and switch the relay.

The Mustang reminds me of the Beach Boy days, have you a car wiring diagram.?
 
very basic overview:

heres what I might try:

circuit to see if ignition is on (i.e. some sort of transistor or relay in a line somewhere that will switch if the line gets powered)

this circuit will drive another relay/transistor that will open the headlight circuit (open = disconnected).

essentially youre just adding another switch next to your "headlight switch" in your diagram there, but that switch is instead a relay that switches it on when the ignition is on, and off when ignition is off.

due to the high amounts of current involved in car headlights (as compared to your average radio shack electronic components), i would suggest relays. you might be able to find some transistors though if you wanted to do it that way.
 
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This could be as simple as using a relay with a 12v coil. Depending on the current the coil will draw, you could possibly piggy back power off the radio fuse, as the radio will have power in the ACC and RUN position.

The current for the headlamps would then be routed though the relay contacts.

Problem with this is if you are driving at night and the fuse blows or the relay fails, you will have no headlights. You could add another toggle switch to bypass the relay in the event that this happened.
 
Thank you for the info guys now comes the newbie part of things how do I begin. I think I might understand what solis has in mind it is what I had in mind but I am very interested in what Andy has in mind. The bad part is how do I determine the components I would be looking at in either case. I know I have a 12v system and that is about all. You have very nicely stated I need things like coil and relays transistors and the like but how do I begin to calculate what ratings these devices need to be.


For instance I do not think I can just put a transistor on the 12v signal wouldn't I need to drop the voltage with transistors and such.

In Andys example maybe I can place a that particular relay right on the 12 volts I don't fully understand his unless the coil is what activates the relay then I do understand his concept but how do I determine the component. Do I just google 12v coil relay???

This is where my newbiness really shows
 
hi Jeff,

Get a dc voltmeter, then near the fuse box check and try to idenitfy the fuses/wiring related to the ignition coil and the headlights.

You need a 12V dc coil relay having a normally open contacts, rated at least 20A.

Ideally the new relay coil would be connected to a +12V ignition wire [ and the other end of the relay coil to chassis] , so it that the relay becomes powered when the ignition is ON.

This will turn on the relay,,, the wiring for the headlights will be 'cut' and connected to the relay contacts.

So,,, ignition ON, relay ON,, headlight circuit enabled via the relay contacts, you will still need to switch on the headlights with the normal switch, when the headlights are required.

If you forget to switch off the headlights when turning off the ignition the relay will open switching off the headlights.

OK.?:)
 
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Thank you very much eric that is exactly what I was looking for. That describes my thought/concept precisely. What is the stability of this added circuit in my searches I found a simple circuit that included a protective diode connected to the Chassis side of the relay and then to the 12V side. in the circuit they describe they have a transistor between the chassis and the relay

The article states this:
Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.

Should I worry about this if I do not have the transistor between the chassis and relay they don't say what drives the transitor...

What do you think about adding a bypass switch that bypasses the relay in emergency or is this realy substantial enough to not worry about it

Thanks
 
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What do you think about adding a bypass switch that bypasses the relay in emergency or is this realy substantial enough to not worry about it

its just a simple switch you can hide under the dash or in the fuse box in case of an emergency. literally run a wire from one side of the relay and another wire from the other side, connect with a switch (with high enough current rating on sw. and wire), and tuck it away somewhere for an emergency. it would cost almost nothing and is a lot safer, regardless of how hefty the relay is. things like vibrations in the car could mess with your connections, that sort of thing
 
Thank you very much eric that is exactly what I was looking for. That describes my thought/concept precisely. What is the stability of this added circuit in my searches I found a simple circuit that included a protective diode connected to the Chassis side of the relay and then to the 12V side. in the circuit they describe they have a transistor between the chassis and the relay

Should I worry about this if I do not have the transistor between the chassis and relay they don't say what drives the transitor...

What do you think about adding a bypass switch that bypasses the relay in emergency or is this realy substantial enough to not worry about it

Thanks

hi Jeff,
The diode in that article is to protect the transistor [ if a transistor is used]

You could fit a relay contact bypass switch, as long as you dont forget to switch it off.:)
A 20A dc rated switch.
 
Well i used a 12v relay in my car.when i lock the car(central locking) the relay controling the lights switches off.it works for me.had it in for a couple of months in.no problems.
 
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