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Electronics Need some help amplifying a small voltage a little

Discussion in 'Modding' started by WILD9, 26 Nov 2007.

  1. WILD9

    WILD9 Been here aaaaages

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    This is actually car related but Its pretty simple. Im after a circuit that will take a small voltage in and pump out a slightly higher voltage but with an upper cap, its a signal line so I dont need to pull much current. The input would be for example 0.7-5v and the output would be say 1-5v so basically +0.4 volts to everything up to a maximum of 5v this needs to be pretty accurate. Also if it doesnt add a lot of extra complexity, being able to adjust the ammount of extra V it adds between 0.1 and 1v with a potentiometer would be great :thumb:
     
  2. Fozzy

    Fozzy What's a Dremel?

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    I dunno if you can. I remember back in the pelt days people wanted to know how to make a 12v psu do 24v but that's a much bigger jump than what you're talking about. Cars run on 12v though so it would be much easier to run a secondary wire from the ignition wire and drop the voltage from there (The ignition should be 12v). Also check your radio, I believe the ACC (Accessory line) is 12v but only on when the car is on
     
  3. WILD9

    WILD9 Been here aaaaages

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    This is a signal line for the ECU, I know cars run on 12V im looking for a circuit to use that to create the output im after with an op-amp or something. It shouldnt be that complicated but its well beyond my mostly forgotten A-Level Physics electronics. btw theres no real problem going from 12v-24v its just you need more power to run devices at the same current which I would imagine is why peltiers caused problems.
     
    Last edited: 26 Nov 2007
  4. Cinnander

    Cinnander What's a Dremel?

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    Hi,
    Run an op-amp between 12v and ground and feed the signal into the + input. Stick a 10k pot between the output (one end of the pot) and the - input, (wiper) which will give you variable gain. Connect the other end of the pot to ground. Adjust the pot wiper 'towards' the output (i.e. low resistance between out and -in) for less gain, towards ground for more. With a 12v supply you'll likely get up to 10.5v out... bear in mind though that without a dual rail supply (eg +12 and -12) you'll only get half the signal.
     
  5. const_

    const_ What's a Dremel?

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    hi

    a simple non-inverting opamp circuit should do the trick, and it will draw no current from the signal wire theortically speaking ofcourse. the image below shows the basic circuit diagram,
    [​IMG]

    you will need to change any of the two resistors R2 or R1 to be a pot, select wisely for the range.

    the circuit being in a noisy environment, you will need some way to compensate for the noise error, i would suggest if you have any electronics/circuits textbook lying read it, seems to me that textbook are much better than google cause everything you need is there and you just have to read it like a bookworm

    also having some simulation programs helps, take a look at oracad pspice they got a student version you may want to try out, and once you decide to build :dremel: the circuit go for a automotive/industrial opamp.

    good luck
     
  6. const_

    const_ What's a Dremel?

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    with a rail-to-rail opamp you can use input/output signal up to the supply rails either (+v -> gnd) (+v -> -v)

    but WILD9, your application dosent require the use of this type.

    steveyg where you at ?
     
  7. cpemma

    cpemma Ecky thump

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    Check out op-amp summing circuits. An LM358 would allow you to use a single-rail supply from the car, a bit like this:

    [​IMG]

    The other half of the opamp could be used as a buffer on the end.
     
  8. WILD9

    WILD9 Been here aaaaages

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    Thanks alot guys, what if I wanted to cap the output voltage?
     
  9. capnPedro

    capnPedro Hacker. Maker. Engineer.

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    Zener diode, compensating for the forward voltage drop somehow?
     
  10. Cinnander

    Cinnander What's a Dremel?

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    Yep, 5.1v zener (iirc that's a fairly common value) or two 2.x zeners in series would work fine.
    Or, if you use cpemma's circuit, you'd have half the LM358 remaining, so you could do something with that (comparator, transistor and probably a resistor needed)
     
  11. cpemma

    cpemma Ecky thump

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    You could be really ghetto and tweak the op-amp supply voltage (LM317). The maximum output will be around 1.7V below supply. ;)
     

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