Need to make a constant .52 volts from a 12 volt source

Discussion in 'The Projects Forum' started by newlitemotorist, Feb 3, 2007.

  1. newlitemotorist

    Thread Starter Member

    Dec 23, 2006
    14
    0
    Hey guys,

    I am working on a special shift kit for automatic cars and I need to simulate a voltage that is .52 volts. The only way I know of doing this so far is to take 7805 that supplies a constant 5volts and run that througha throttle position sensor which is then adjustable down to .52.

    I was hoping there was a way to take an LM317T and use other stuff from radioshack and make a constant .52 volts.

    Any help would be much appriciated!!!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    That would work fine if the signal load is constant. Put a 5000 ohm pot across the 7805's output and ground, and diddle the wiper to .52 volts. Use a 20 turn trimmer to make life easier.
     
  3. newlitemotorist

    Thread Starter Member

    Dec 23, 2006
    14
    0
    I am completely knew to this stuff so please forgive my ignorance here. So I would use the 7805 to get the load down to a constant volatage, then hook that up to the adjustable regualtor. Also, how do I "diddle" the wiper to .52v??? Are there some laymens terms you can use or maybe just tell me what to get and where to hook what up?

    Thanks again.
     
  4. dragan733

    Senior Member

    Dec 12, 2004
    152
    0
    I would not use a pot with purpose to get 0.52V, as the pot has bad temperature characteristics. I would use stable voltage reference diode and OPAMP that will set the output voltage to 0.52V.
     
  5. newlitemotorist

    Thread Starter Member

    Dec 23, 2006
    14
    0
    Can I get that stuff at radio shack??? It would be really nice if I could....also if you would please explain how I would put this together.

    Thanks
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    A precision voltage source could be made from an OpAmp - if the current requirement is not too high. How many milliamperes are needed here?

    "Diddle" means, um... well... it means "diddle." As in "diddle around." Or "fuss with."
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There should be a stated requirement for the accuracy of the .52 colts. If it's going to be between .5 volts and .550 volts, then the regulator and potentiometer will work very well. If the requirement is .515 volts to .525 volts, then you may need a voltage reference and op amp to get and maintain the accuracy.
     
  8. newlitemotorist

    Thread Starter Member

    Dec 23, 2006
    14
    0
    The voltage could be from .51 to .53 volts......I just need to get it in the general area in that range!

    So I guess the regulator and a potentiometer will work? Any ideas on how i would need to set this up?

    Thanks again
     
  9. newlitemotorist

    Thread Starter Member

    Dec 23, 2006
    14
    0
    Hey guys,

    I was just wondering what kind of potentiometer I would need to get.....how many ohms should it be? how many watts??? Radioshack has some but I dont know if I can use them.

    Thanks
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you're using the 7805, then 500 to 1000 ohms should do. Get a trimmer. It will be inconviently small, but the adjustment is over multiple turns so the ability to set the voltage off the wiper is vastly inproved.
     
  11. Spoggles

    Well-Known Member

    Dec 2, 2005
    67
    0
    Hello:
    Why not use a split +5- 0v- -5v supply, connect the lm317 from +5 to -5v and adjust the output for 5.52v as referenced to -5v.

    You would then have a stable 0.520v supply to 0v.

    Spoggles
     
  12. newlitemotorist

    Thread Starter Member

    Dec 23, 2006
    14
    0

    I will be using a 7805.....I bought a 10k ohm cermet potentiometer that has a 15 turn wiper adjustment....will this work for what I need?

    Also, what kind of capacitors do I need to use for filtering? I currently use 10uf capacitors to filter the 5volt regulator I use.

    Thanks again.
     
  13. renginear

    Member

    Feb 22, 2007
    11
    0
    I am probably late on this...but have you looked at Digikey online. They usually have most components and in your case they would have all your parts.

    You have to get it shipped to you ($5 by ground) but you can get everything in one shipment.
     
  14. rwmoekoe

    Active Member

    Mar 1, 2007
    172
    0
    i think this idea is good.

    by the way, what is the condition in which this power supply is gonna applied?
    in a car, or what? please describe the exact need of the current level and accuracy. maybe it'll help us to tell a bit of the apparatus in which you're gonna fix this thing...

    thx
     
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