5V or 12V TPS?

Whatever you do it will need voltage stabilisation, your nominally 12v system will vary between 9 and 15volts in use so could not give a reliable output. I would go for a 5volt system as that seems to be the most common used by many manufacturers and there must be a reason for that. 0- 5 being the way ford do it.

Mrcheerful

Nedavno Mrcheerful napisa:

You are right, I wasn't thinking...

Yes, I'll fabricate 5V stabilizer... Nothing is as simple as it seems at the beginning... :-)

1: You can't get 12V from less than 12V easily. 2: 5V is most common volt reg (read cheap) as it's TTL voltage so a 3 pin IC voltage reg does the job with a part count of 1.

Nedavno Peter Hill napisa:

Yes, I have IC 7805. And it's easy to fabricate voltage regulator too. What is not easy (read boring), is to find the place for it out of site in the car, and safely wire it to the car electrical system.

Thanks to all.

7805S might be a safer bet as it's rated at 2A, not 1A. Doesn't need to be massive. All you need is the 7805 and a heatsink with 12V in, 5V out and ground. Being a bit cunning you could solder the ground to the heatsink and use a self tapper to hold the heatsink to a metal part of the body. Done right, you should be able to make it no bigger than 1"x 0.5". No need to f*ck around mounting it on veroboard or knocking up a PCB.

Conor explained on 08/11/2008 :

The heatsink mounting tab is directly connected to the middle ground pin internally. Just bolt the heatsink to ground, then just 12v in and

5v out wires to solder - add a bit of sleeving, job done.

Nedavno Conor napisa:

?????????? 2A? I was thinking of using LM78L05 with output current of

100mA.

I connected TPS to 5V, and it draws only 9.8 mA. So 1A or 2A is way too much.

I think I do not need heatsink. I connected TPS like this (a bit of ASCII art, I hope it looks OK :-)

+12V | R | ------------- | | Z TPS ---- 0-5V signal that I need | | ------------- Ground

Where R is 1Kohm resistor, and Z is unknown zener diode. It is connected now for about an hour, and it is not even warm to touch.

Nedavno Harry Bloomfield napisa:

That is also a good idea, thank you.

Err, why do you think 'they' use 5v? Apart from it being common for electronics it will also be stable - unlike the so called 12 volt supply on a car which can vary by about 30%.

In message , Conor writes

78L05 might be an even better bet, it's only 100mA but it's a TPS pot he's powering not a ZX81. If he needs more than a couple of mA then there's a real problem with his wiring.

Don't forget the bypass caps and reverse diode but otherwise can't fault what you say, it could be really neat and tidy if done right.

Bypass cap? WTF is that?

Nedavno Conor napisa:

I think he is talking about this:

Ah. Now it makes sense. So actually, it's a capacitor to smooth out the ripples in the input and output and Clint doesn't know what the f*ck he's on about.

If you take the trouble to read the blurb on 7805's (and other similar regulators), they need a capacitor on the input and a smaller value on the output to prevent them going into oscillation. Generally with a low input impedance source such as a battery, there is no problem.

A diode on the input is only of value for protection against reverse polarity. If there is little likelihood of this happening, as with this use where it will be connected once and forgotten, it has no value. If the heatsink is bolted to ground, again it has no value as there is no possibility of accidently reversing the connections and doing damage.

And back EMF, a high probability in a system with an alternator.

It happens that Conor formulated :

If you wanted to achieve that - you would put the diode across the supply, rather than in line with it.

This is the definitive 1A regulator circuit:-

It requires a minimum load to function correctly - 20mA or so is fine.

Dave Plowman (News) formulated on Sunday :

What exactly makes that circuit the 'definitive' one?

Nedavno Harry Bloomfield napisa:

Harry what is your opinion, is LM78L05 with output current of 100mA enough, or do I really need 1 or 2A? I tested the circuit, and it only draws 9mA.