Electronic – Detecting a low pulse from an electromagnet induction


I am designing something similar to a coil gun. So what I have is a magnet passing through/adjacent to a coil. Due to the electromagnetic induction, I do get a pulse(triangular) across the coil. However, the amplitude of this pulse is very low to detect, as its around 60mV peak.

I tried using a comparator(LM311) for detecting that low voltage, but noise disrupted the operation, as the noise level was also high.
Is there something I can do to detect that pulse?

Things I thought about :
1. Increasing windings on the coil
2. Using a stronger magnet
but apart from these, is there something that can help me achieve the same?

Currently the coil used is a small sized with about 30 turns of around 23-25 gauge magnet wire

UPDATE: I tried increasing the resistance by adding a 1Kohm-100Kohm in series to the coil, but it did not increase the voltage much. I also tried winding a coil with more turns but still the max voltage was around 40mv.
Also, here is a video: http://www.youtube.com/watch?v=hajIIGHPeuU I came across. The current generated in this case is 20uA, which for a resistance of 1Kohm, should give a Voltage of 0.02V. Any other way, I can increase the voltage level. Would having a core help in anyway?

Best Answer

There is a little amplifier I am very fond of which I have used with dynamic mics. Since your coil situation is much like the one faced by someone trying to amplify a dynamic mic, I encourage you to try this circuit and see if produces a usable signal. Just replace the "microphone" (speaker) with your coil.


The lower transistor acts as a common base amplifier, which is fairly unusual. It has a current gain of less than 1, but it does provide significant voltage gain. The upper transistor is in a common collector configuration, so it has essentially unity voltage gain, but the current gain is good. In short, this first amplifies the voltage, then the current, to give you a strong output signal. Although you will likely need a second stage after this, that should be much easier.


Concerning your noise issue, do you know where the noise is coming from? Sometimes I just have a power supply that's super noisy and ruining everything. I like low budget solutions, because of, well, my budget, so I usually test this by running the circuit on batteries. If things start magically working, then it's time to work on the power supply.