Newbie Hello and Help With Schmitt Trigger

Hello. I am new here and am a hobbiest/tinkerer who has no formal electronics training but who is self tought on an as-needs basis = I have little knowledge :(

I am currently working on a data logging project using an Arduino. The specific sub-project I currently require help with is taking a sine wave signal from an induction sensor and converting it to something that the Arduino can use for engine RPM calculations. (I know a hall effect sensor is much better for this but I have the induction sensor already installed and need to use that).

The induction sensor is outputing a sine wave that has a peak to peak voltage that varies with engine RPM. At engine idle it can read as low as around 8v P2P but at redline may read around 100v P2P.

For my final RPM calculation I will not reference the quantum of the sensor voltage output and also need to restrict it to something that the Schmitt Trigger can handle. I therefore propose to use a pair of Zener Diodes with bias voltages to clip it to +/- 4.7v (or thereabouts).

This clipped voltage then gets processed by an Op-Amp that unlimately generates a square wave output of +5v/0v that the Arduino can use.

After many (and I mean maaaany hours of fudging around) I have come up with this;

This is a public project so I am not sure if I should be pasting a URL to it or this screen image?

I have run a simulation using a sine wave P2P of 100v on a 1Hz cycle (didn't go faster as it gets hard to see the resultant graphs properly). It appears to work..........

I have a couple of questions however;

  1. Can somebody with electronics knowledge (as opposed to my guesstimation!) look over the circuit and comment?

  2. As I need the final output to be +5v or 0v I had to connect the Vcc +/- backwards. The simulation allowed me to do this but can it be done in reality?

  3. The trigger points that my resistors produce do not match a Schmitt Trigger calculator that I found. These resistor values should give an output high voltage at 0v and a low value at -0.833v but the simulation graphs don't appear to agree with that. The sine wave signal may or may not be clean so a little hysterisis (correct term?) will be a good thing. In an ideal world I would like the output to set high at a sine wave input of 0v then set low at something like -1v. I have not been able to achieve this....sighhhhhh

Your help is greatfully appreciated!

by mk1_oz
August 24, 2017

No Answers

No answers yet. Contribute your answer below!

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.