# How to reset an integrator ONLY with RLC and op-amps?

I am trying to reset an integration circuit that is designed like above -- but obviously with another resistor attached to the op-amp positive input side as well. I have used 4.7k$\Omega$ resistors for both and a 1$\mu$F capacitor for C1. (I just did an experiment with this design and it turned out to work, so I didn't change it)

But the problem is that I want to reset the integrator every 5ms but without using anything else than resistors, inductors, capacitors and operational amplifiers. I have tried replacing the switch with two series 500mH inductors, and that circuit did reset the integrator but I have no idea how to use the output(the only thing that noticeably changes seems to be the minimum value of the output voltage). Any ideas on how to do accomplish this? :(

More details on what I'm trying to do: I'm using an ultrasonic sensor which gives me a 5V pulse starting when the ultrasound is fired, and until it is reflected back -- i.e. the pulse width is proportional to the distance between the sensor and the object, so I'm using an integrator to measure the width of the pulse. I am measuring the distance every 5ms, as the object gets closer and closer to the sensor from 50cm away. I got the number 5ms from the time it takes for ultrasound to travel 100cm(50cm back and forth), which is about 3ms, and just added 2ms as the time for the integrator to reset.

Any help would be appreciated, I've been stuck on this for this entire week :(

• Why are you choosing to tie your hands behind your back, exactly? – Finbarr May 31 '17 at 10:48
• @Finbarr I'm actually trying to implement this for my term project(we're allowed to seek help online) with the weirdest regulations ever :/ I tried to sneakily use some LEDs(allowed) as diodes like this but the professors dont seem to like this either – L J K May 31 '17 at 11:19
• Resetting an integrator is implicitly not a time-invariant or linear operation. There is no way to do it with strictly LTI components. The best you could hope for is to exploit some nonlinear behavior of a real-world opamp. – Dave Tweed May 31 '17 at 11:36
• If allowed, using comparators (which are a kind of opamp) with open-collector outputs would eventually allow you to solve this. The exact circuit, however, depends on things you didn't specify (the polarity/range of the signals, accuracy, ...). – dim lost faith in SE May 31 '17 at 11:40
• No, uA741 does not have an open collector output. But actually I think you should talk to your professors. They can't expect you to solve it this way. If you can't use transistors (which are the right component to solve this), it just complicates things more than it should. I'm pretty sure they don't put these restrictions for the only sake of complicating your life, so there is either 1) something you didn't interpret well in the project constraints 2) or these constraints shouldn't apply in your particular case 3) or the project itself is unfit for these constraints. – dim lost faith in SE May 31 '17 at 12:56