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figuring out what resitor to use... — Parallax Forums

figuring out what resitor to use...

willthiswork89willthiswork89 Posts: 359
edited 2006-07-23 21:51 in BASIC Stamp
okay i figured out i need a resistor to take off .5 Volts

im trying to use ohms law to figure out which resitor i need

V = I X R

i know that the voltage is 4.5 and im not sure about the I but i guess

R = V % I

how do i know what the value of i is ?

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2006-07-23 02:26
    What exactly are you trying to do?

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • George99George99 Posts: 16
    edited 2006-07-23 02:29
    What device or circuit are you dropping the voltage for? You need to know how much current it takes, either the manufacturer's specs or measure it.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-07-23 02:36
    Shoudn't this be asked in The Sandbox?
  • willthiswork89willthiswork89 Posts: 359
    edited 2006-07-23 17:54
    well i was trying to run a RC receiver from my bobot and it takes 4.5 volts i wasnt sure if 5 volts would mess anything up so i was thinking i should use a resistor to knock off that .5 volts but i didnt know about the I...
  • aalegadoaalegado Posts: 66
    edited 2006-07-23 18:30
    You can't solve Ohm's law (V=IR or I=V/R or R=V/I) without two of the three values.

    If you know you need to lop off 0.5V you will have to come up with the current draw, I, of your device so you can solve for R=0.5/I

    Alternative: You could put a switching diode in series with the device. A switching diode like th 1N4148 will drop about 0.7V. That might be too much. A signal diode may drop a little less voltage but might not be able to handle the current your device draws. Again we're back to current draw... tongue.gif

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    I wouldn't connect that if I were you...

    Vive Le Tour!
    July 1 - July 23
  • bennettdanbennettdan Posts: 614
    edited 2006-07-23 21:49
    I run my reciever of my RC radio fine on 5v with no problem, but if you want to drop it down then you can use a 1N4001 or 1n4003 diode it will handle 1A with about 20A surge and drops about .6 volts. When I put a volt meter on my BOE it only reads 4.85v I bet if you check your battery pack to your reciever it will not be off of this voltage much.
  • willthiswork89willthiswork89 Posts: 359
    edited 2006-07-23 21:51
    i just used it anyways i dont know the current draw because the chip is not my design and it would take a ton of time to find it
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