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  • EEVblog #471 – Overload Detector Circuit Design

    Posted on May 18th, 2013 EEVblog 17 comments


    Fundamentals Friday
    Dave takes you through designing a signal overload detector circuit from scratch and then builds it up on the breadboard.
    Window comparators, schmitt inverters, capacitor charging, pulse stretching, common mode input range, tongue angle tweaking, it’s all here.

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    • Stephen

      Dave

      Really enjoying this new segment it is a wonderful complement to the tear down tuesday, have any motor controllers for large 1 to 10 hp motors DC or AC show up in the junk that would be a good tear down and fundemental combo show

    • Kal

      Dave

      I really love your videos, they are always educational and alert me to problems I would have otherwise banged my head against for hours.

      It would be nice if you could explain why the thresholds to switch the LED on/off are not so precise. With reasonable precision resistors (1% or better) I would really expect the LED to turn on almost bang on at 2 volts or 1.25 volts. Why doesn’t it?

    • http://am.co.za/plasma Eric Yin

      Awesome, loved this segment. I had to watch the RC explanation on the capacitor changing almost two times (the high and low voltages were confusing me), but i got it at last. Keep sharing the knowledge. Thumbs up!

    • J.R. Stoner

      I have been fascinated with the concise analysis of this circuit. I remain, admittedly, one of the “young players” you mention so often (no matter how ancient I am, in fact). I have posted a project circuit which adapts this and uses it to switch the gain on a power amplifier. Hopefully, this is a good enough design to allow AGC cutoff if the input mic would otherwise clip the power amp output. This is for a possible “de-ess” mic amp. The project identifier is P01-119A.

    • Gordon

      Dave, this is brilliant. I wouldn’t be surprised if Fundamentals Friday becomes your most popular material. I bought a t-shirt as a way of saying thanks.

    • tchicago

      Can also implement the Schmitt trigger using a quarter of that same LM339, so the whole thing will fit one DIP14. (and I’d use the last remaining quarter as a LED amplifier after the Schmitt, because the open collector loaded directly on LED will make the Schmitt parameters less predictable)

      Actually, I think such a fundamental element as a Schmitt trigger and its implementation on a comparator or opamp deserves another episode. That’s where you’ll have to give a positive feedback. :)

    • Ludzinc

      Love your work Dave.

      Think I’ve spotted a minor error with your reference voltage on the comparator usedvto switch the LED.

      VREF there should be 63% of Vcc, not simply 0.63V.

      Like I said, minor error. Well done!

    • Atte

      Hey, nice circuit and video altogether, newer thought it would be that ”easy” :D great work dave :).

    • Wonko the Sane

      Minor point, when testing the trip points it would be easier if you disable the pulse stretcher as it puts in a delay….

    • sm7xvd

      I think fundamentals friday is a really good idea.
      For myself having skipped many basic aspects of electronics design and gone on to microcontrollers and digital stuff it’s great.

    • f4eru

      Another trap :
      if you use an OP amp in place of a comparator, beware ! some models have a pair of antiparalell diodes between in+ and in-, which conduct as soon as the OP leaves the linear region !!

    • http://Cynaps.com Hedley

      Fundamentals Friday is the highlight of your site . Way back when you did the dc to dc converter tutorial which was spectacular I check in weekly for more of the same . What happened to the USB power supply project ?.

      Perhaps a topic that we could all benefit from is inputs and outputs from micro controllers setting out circuit analisys ie voltage and current at each node and how to calculate these . Transistor , fet , relay , lec out and then input protection . Many of us use 10k pull-ups . 100 ohm in line and clamp diodes without knowing why .

    • John

      I now cut the leads before I remove the resistors from the tape thingy. Avoids the bending of the leads and the loose lead bits.

    • michael

      i envy you… 24.8°C vs 7°C here.
      fundamental Friday is great.

    • achim1989

      Hi Dave,

      nice video as always! :D

      One thing I noticed for the first time in this video and which is bothering me since then:
      You’re using the european resistor symbol when draw schematics, and not the american zigzag one… any special reason for this?

      You’re doing great! Keep it up!

      • http://www.eevblog.com EEVblog

        No real reason, I use both all the time.

    • http://www.focuspdm.com/services/electronics-design.html Electronic Design

      Nice video now you get latest electronic design.