12v lm1086ct powered 3v compass

Discussion in 'The Projects Forum' started by thelazygreenfox, Mar 11, 2012.

  1. thelazygreenfox

    Thread Starter New Member

    Mar 11, 2012
    Guys I'm trying to convert a suction cup mount 3v (2x AA) compass w 4 leds to a permanent 12v dash mount in an instrument pod.

    I've soldered an lm1086ct 3.3 v regulator w 1.5uf caps from the in and out to ground on the regulator pins. Then soldered wiring to the in and out pins.

    With 13.5 v in there's only 1.7 v at the output pin. Could I have killed the 1086 or caps by soldering them to the 1086 pins?

    Next I traced the circuit board power and grounds, then carefully cut out the 2v parellel led circuit and powered it from 4 individual resistors. This to be powered from my van lighting circuit. Leds work okay.

    It's very time consuming but a great project and if it works will be a unique option for my 4x4. Not my field of expertise but I've done worse.

    I'll be reading "all about circuits" but needed a helping hand on this project. Great site, gives confidence.

    Thanks for the help.
    Last edited: Mar 11, 2012
  2. jtrent

    New Member

    Mar 11, 2012
    You may have a different LM1086 rather than the fixed 3.3 volt version. If this is the case, you would need to modify your circuit slightly to change the reference voltage. Don’t connect your reference to ground, instead connect it like the diagram below.

    Sorry, couldn't get diagram to load. You can see my diagram with full response at www.MoreDat.com Not sure if I can say this but I don't know how else to get you the circuit diagram.

    You will need to select appropriate values for your resistors to get the desired output voltage. Formula for output voltage is:
    V_(out )= V_ref (R_2/R_1 )+ I_adj R_2

    The above refers to the diagram that I tried to upload. I composed my response in Microsoft Word. If you can help me with how to get my response from Word to here without loosing the diagram and formulas, that would be helpful.
  3. thelazygreenfox

    Thread Starter New Member

    Mar 11, 2012
    If the file size is 2 MB or less it should load, but U can convert it to a PDF file (5 MB) and load as an attachment under "manage attachments" below.

    If this is the incorrect regulator I will change it for a 1086it as the ambient temperature specs listed aren't appropriate for my needs. The compass will frequently operate below freezing.

    Bypassing the 1086 with a resistor will determine if the regulator is inadequate.

    I would prefer to not use resistors as it complicates the project. But....

    Where is your diagram at moredat.com. Need directions.