Very low Signal/voltage level

Discussion in 'Embedded Systems and Microcontrollers' started by JDR04, Jun 18, 2015.

  1. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    I have attached a schematic in the hope you kind folk can help me on this one.

    I have a DARK DETECTOR which is controlled by a small program in a 12F683 microcontroller. My problem is the voltage level (about 40mA) from the LDR does not allow me any room to set the light threshold level with the potentiometer.

    Is there any way the 40mA voltage level can be amplified or is there a better way of achieving this?

    Thanks folks..............JDR04
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Sure, make R5 about 50K instead of 5K. The goal is to find a value of R5 where it's resistance is about the same as the resistance of the LDR at the illumination level you want to detect.

    And don't you mean 40mV; instead of 40mA?

    You really don't need an ADC input to the PIC at all. If you set the right ratio of Rldr to R5, you could just use a port pin as a crude comparitor.
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,380
    494
    milliamp is measurement of current. Not voltage.
     
  4. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Thanks MikeML, I'll give that a try.
     
  5. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    You're right, thanks for pointing the error out.
     
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