Adding Logic Based on Two Sensors

Discussion in 'General Electronics Chat' started by jaytothex, Sep 9, 2014.

  1. jaytothex

    Thread Starter New Member

    Sep 9, 2014

    I am just getting started with creating electronic circuits. I have been able to a work out a couple basic circuits using an input (sensor) to illuminate an LED when a certain condition is met based on some sample circuits and tutorials. For example, a light sensor that represents the amount of light it is detecting in mV (higher light = higher voltage), and when a threshold of at least 500mV is met the LED illuminates.

    That is all good and is helping me start to wrap my mind around the basics. But I have some of my own basic things I want to design to keep me motivated and where I am at with my own circuit is I am struggling to understand is how to add logic without a micro-controller. I know how to solve the problem using an Ardunio, but I am trying to learn ground up circuit design and wanted to create a basic circuit that has two identical sensors, compared the voltages of them, and if sensor A > sensor B, the condition is met, which what I am working to is a relay would be triggered, but for starters I am just trying to get an LED illuminated. If sensor B >= sensor A then nothing happens.

    Can anyone point me a simple example of such a circuit or offer some guidance on how one could go about it in its most simple form. I am a total laymen at this point, just doing example circuits and trying to understand how it works the way it does.

    PS: Off topic, but I have been looking for good circuit design/simulation software that is geared towards the novice, where there is some reference/training built in. My search only turned up some older software that didn't seem relevant anymore. Is there anything like this, and what is currently top offering if there is such a thing, or perhaps the first piece of software a newbie should invest in to help with their progression?
  2. Alberto

    Active Member

    Nov 7, 2008
  3. pwdixon


    Oct 11, 2012
    You need a comparator, it's like a logic version of an amplifier. Pick a comparator from your favorite chip supplier and look at the datasheet there'll usually be a simple application circuit that should be enough to get you going.