Connect with us

PIR light circuit

Discussion in 'LEDs and Optoelectronics' started by KTW, Feb 22, 2015.

Scroll to continue with content
  1. KTW


    Feb 22, 2015
    Hello, I'm building a 12 volt 48LED light panel circuit that will operate off a PIR sensor with a 9 volt DC power supply.
    There will be a LDR built into the circuit so the light stays off during the day.
    I'll have a npn transistor within the circuit so I'm trying to determine the value and placement of resistors.
    Considering the light panel is designed to operate directly from 12 volts DC I shouldn't need a resistor in front of it but I think I may require a resistor to protect the transistor, just not sure what value.
    I may also add a variable resistor to control the LDR.
    Thanks for any advice you can offer.

    Attached Files:

  2. duke37


    Jan 9, 2011
    The LDR should not be in series with the LEDs, this should be replaced by a current control resistor. A base resistor should be added to control the base current. More information on the panel and LED assembly would help.
  3. KTW


    Feb 22, 2015
    Thanks Duke.
    The LED panel is like this one

    These are designed for 12 volt automotive use and I found where someone had placed a value of 230mA on them.
    The LDR is necessary for the circuit to work on it's own during the night.
    I have a similar circuit built and it's working but I want to add the photoresistor.
    I don't have any resistors on this circuit but I know there should be one or more.

    I was looking at this also as an option.
    Last edited: Feb 22, 2015
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day