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Feedback on 555 timer Schmidt Trigger design

colporteur

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Can I get members insight into using a 555 timer as a schmidt-trigger design that I pulled from the Internet?

I found this schmidt-trigger design using a 555 timer. I would like to use it to condition the output of a photo-resistor. The 555 timer output will feed the input to a Arduino Mega. I'm in the process of bench testing the setup to finalize component values. While testing I figured I would throw it out to some more enlightened minds than mine for feedback.

I'm using the 555 only because I have a stock of them. I don't have any readily available smidth-trigger IC's so I figured I would go with what I have and build from scratch. Building from scratch especially using Internet designs comes with risk. I was hoping to mitigate the risk by getting community feedback.

If inquiring minds suggest you don't want to do this, that is a good thing.

  • 0 in reply to colporteur

    You may have the ability to measure capacitance with your DMM. Usually the lowest range is in nF, but 0.001nF = 1pF. You can get a rough idea that way of how much change there is.

    Or build my device that uses two 555 timers to measure capacitance. It uses the display on your DMM, where on the lowest range, 1pF is 1mV. On the lowest scale, most DMMs can measure down to 0.1mV, so you can have 0.1pF fine grained measurements.

    https://hackaday.io/project/183405-dual-tlc555-capacitance-meter-01pf-resolution

    How accurate depends on the capacitor you use to calibrated it. Let's face it, 5% is fine for 99.999% of what we do, so a capacitor between 100 and 200pF is good to go, even if it is 5% or better tolerance. Lots of mica capacitors in that range are 2 or 3% tolerance.