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Mechanical Engineer, total electronics NOOB!!!

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KeepItSimpleStupid told me to say this, so here goes:

I am a noob when it comes to electronics. And I've joined this forum in the hope of getting some practical advice to realise me theoretical visions. I'm going to post a few projects here, some of which may never be built, others which I am hoping, no, going to build.
 
My first project may never be built (for non-electronic reasons), but I'm still hoping to extract some useful info from this for future projects.

Here's the scenario:

My car has four headlights: two driving/dipped lights, and two foglights. The lights are powered by the main switch, which also turns on the front fog lights and then the rear foglights (but I'm going to ignore the rears). The column switch activates the driving lights when pushed forward, which turns off the dipped beams. Pulling back on the column swich also turns on the driving lights, but only to flash - a spring returns the switch to centre (i.e. dipped beams). The first schematic is my approximation of how this works. I have omitted the main switch, since that is assumed to be always on for the purpose of this project. The flash switch is included, though.

In South Africa we seldom have use for the foglights, so I was thinking about converting the fogs to spotlights instead, and connecting them to the driving lights. Then I had a brainwave: Why not convert them to fog/spot combination? The main lights use H4 bulbs, so too could the fog/spot combo. Now I would need some logic to prevent the spots being on at the same time as fogs (except, maybe, when flashing), since driving conditions usually render the two mutually exclusive. I don't really want to modify the switches of my car, but maybe I could use a transistor to switch off the spots when the fogs are on, or to let the spots be switched on by the driving lights when the fogs are off.

The second circuit is an approximation of this setup. I have also included what I believe to be a "truth table" of this setup. So first question: could this actually work?
 

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  • Headlights1 - Sheet1.pdf
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  • Headlights2 - Sheet1.pdf
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  • Lights logic.pdf
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The transistor symbol I used is just representative of a transistor. I am not sure whether to use FET, BJT, NPN, PNP or whatever, even unsure about how many. But please keep these details for when I get more specific.
 
I dont think you will need logic for this but just an extra switch for the "prevent the spots being on at the same time as fogs " adding transistor switches will require just as much rewiring, plus then a CONTROLer device

A NPN transistor works so the "light you are switching ground" is connected to the collector, the emitter goes to "circuit ground" and the base commands the switch(usually with a lower voltage)
Transistors are a bit complex, it s better to learn the basics first, ie. ohms law, curchovs law, and such, before trying to understand and calc. GAIN.... and TOLERANCE


here is a good starter tutorial:
http://www.kpsec.freeuk.com/trancirc.htm

for 300$ I got an first yr cd rom from a local college,

heres one for only 10$ :**broken link removed**
(i dont know if this is actually what you want)

I found it hard to understand your description of what you actually want(in the end)(sry bad eng, if you could simplify?) If schematic 1 is wired ideal if thats how you want it to work, but schematic 2 gives me spins!! pls re-specify spot lights role!

turning on YOUR transistor would cause FOG and BRIGHT to power similar, ignoring the biasing faults, and the bad wires at the base,,

MAY I suggest using a RELAY in diagram, , way simpler for you to explain your methodology!
 
I am doing this for the specific purpose of teaching myself. I am going to use relays to turn on the lights, so that the wiring loom doesn't have to work so hard, but I need to usnderstand how to use transistors. I have never heard of "relay logic", and relays wil serve me no further purpose during the course of this project thread.

Headlights1.pdf is how my lights look now. Headlights2.pdf is what I want. Also refer to the truth table.

I don't want more books, as the ones I have mean no more to me than the ones I can still get. I need a practical education.

BTW, is my English bad, or is your English bad? I think your English is good...
 
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I already stated that I do not want to mess with the existing switches of my car. I don't really like conversions, but if I do a conversion, it must look like came out of the factory that way.

I also may not need logic in this circuit, but I'm trying to learn a little about logic, and this uses nice binary numbers. I'll see what I can do to state the question more clearly, and make more visible thumbnails...
 
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relays are similar in the sense that they handle switching good, and you only need to worry about min switching voltage and max V/I values and stuff, transistors are a little more picky with switching voltage/current @ the base, since it needs to achieve a perfect state of "saturation"

best thing to do then is to follow the link,

http://www.kpsec.freeuk.com/trancirc.htm

I started with NPN, i find it simpler, first you need to get the current of your switching device ie headlight, then you divide it by the GAIN of that transistor, with the answer to that you now have the current you will require to turn it off and on(at the base). simple... I prefer the 2n2055 since it goes up to 5 amps and has a gain of 80, but i doubt 5 amps is high enough current to power a headlight,. another reason why I'd use the transistor to switch the relay, as in the examples, (thats just me thou, there may be better ways!) and then I'd more likely use a tip31a or tip121 (get 2nd opinion thou!)

emitter goes to ground, collector goes to headlight-

btw, your eng is OK, i just loose track in the description,, if you redraw schematic2 the way you want it to be with added "normal switches" It will be easier to add the logic control you desire( ie, instead of using that transistor, use a switch, and draw an arrow to where you want that switch to follow (be controlled from!))
 
KeepItSimpleStupid told me to say this, so here goes:

I am a noob when it comes to electronics. And I've joined this forum in the hope of getting some practical advice to realise me theoretical visions. I'm going to post a few projects here, some of which may never be built, others which I am hoping, no, going to build.

You can find several tutorials about transistors and how they work! There are also some videos in youtube.
 
...which still helps me nothing in terms of knowing how to select them. If three text books and four semester courses left me none the wiser, and I always received to components for my University experiments, how is anything other than bankrupting myself going to help me develop a practical approach?

Please help me to explain to you all what I'm trying to accomplish. What doesn't somebody understand about what I'm hoping you will help me with?

And how do I rename this thread?

I'm hoping that others would be able to benefit from my stupid questions, but right now I feel like the only one not benefitting...
 
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That's a very strange University.

Back in old school days some of the first to learn after the most basic was to read and understand transistor datasheet and books with tables and maximum/minimum/typical values for a large number of parts.
 
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Sure, if you're an electrical engineering student. I was a mechanical engineering student. We were required to purchase drawing/draughting tools, measuring equipment like vernier calipers, internal and external protractors, stuff we could use. Also, very expensive bearing, fan belt and chain catalogues and data sheets.
 
Its not as easy to power halogens with transistors as you may think, since they are so high power and need heatsinks

THE link i posted twice now is the simplest you get with transistors, which powers a relay, which is what u should use to switch the halogens, in that order. (and protection diode)

use a TIP31a transistor, put a heatsink on it, get a relay that can run the CURRENT of the halogens,
(we need to know the power rate of the bulbs you are using if we are to calculate specific values)

(others would recommend using a mosfet, but im not that smrt!)

also if you want to start playing with this stuff id suggest at least getting a 20$ voltmeter, if you are to be building circuits get a breadboard and some wires! AND if you don't know ohms law yet you are in way over your head learning about transistors.
 
Even if I use relays to power the light bulbs dircetly, the transistor as a switch will only be required to actually allow this or that relay to switch on. My question remains:

1. Fundamentally speaking, could this work? Forget about specifics - this or that type of transistor, power capacities etc. Could I use simple transistor logic to control which beams to be lit up mutually exclusively?
2. Fundamentally speaking, which direction of which configuration of transistor should I use? NPN, PNP?, Common emittor, common collector, common base?

I'll ask my questions like this when I get there...
 
1) sure it could work, transistors only? maybe if you use several, technically yes, but no since they will get super hot and need super cooling! fans ect...a ton of junk

2)you can use logic to control any combination you want, the configuration you should use IS in the link i posted twice about half way down that page; "using transistor as switch" section, also read the section under it "using relay"; then read section under that "when to use a relay" , it answers all your questions, THe transistor in THAT example is NPN, with common emitter,, called that because common is another name for GrounD , and the emitter is going dirrect to it.
 
I think there should be a special website for NOOBS that I will never go to.
Then they can talk their nonsense and not learn anything about electronics.

I know almost nothing about plumbing but I don't post nonsense on a plumbing forum.
Oh, my natural gas heated water heater has low output pressure. I betcha if I posted the question about it then I will be told to replace the water heater.
 
I'd ask what output pressure? Gas, water, or air from a power vent. If you said the latter, I'd say check for a clogged vent by say birds.
 
Lights

From your drawing it doesn't look like the flash is correct - no flash if dims are on.
But that's not relevant.
Here is a circuit that should do it.
It may need a bit of a heat sink.
Basically spots are on if brights are on and fog switch is off.
Be careful of the current in both the wires and the switches.
Oops, better make the 470 ohm resistor 1000 ohms - a bit to hot.
 

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    lights.PNG
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