Interfacing a piezo to an arduino

[Rx7man]

I'm looking to build a device that takes a pulse from a piezo crystal and interface it to a microcontroller.. I know the piezo is a very high voltage device, so I need to find some way to make it compatible.. I looked it up on the Arduino site and it seems like a terribly primitive method to use a 1meg resistor in parallel with it.
I was thinking perhaps a VR sensor IC chip like the MAX9924 which is capable of some noise filtration, zero crossing detection, and I need them in my project anyhow.
https://datasheets.maximintegrated.com/en/ds/MAX9924-MAX9927.pdf

The application is a diesel engine timing monitor, I'll have a VR sensor on the cam gear (10* per tooth), with a hall effect sensor to sense #1 cylinder position, the Piezo crystal.. Something like what's shown here https://www.amazon.com/dp/B00063Y1LU/?tag=pfamazon01-20I may need to play with the resistor values a bit, start with more resistance and lower it until it works

Open to other ideas, maybe there's a specific chip for this? I didn't see anything when I searched Mouser

 

[Averagesupernova]

What's the dynamic range? The first thing that comes to mind is a log amp coupled with an automatic gain control, etc. Sorry I don't have anything specific.

 

[Rx7man]

I'm really not sure what the dynamic range is going to be! I'm going to have to build the piezo clamp first.

Only thing that makes me question the MAX9924 chip is it usually gets a sinusoidal input and I don't know how it'll like a very peaky input..might be some trial and error there

 

[Rx7man]

I sent a tech support question to Maxim.. maybe they have an idea.. worth a shot

 

[berkeman]

Sorry, I'm not understanding the piezo transducer part. AFAIK, a piezo transducer converts force impulses to capacitive voltage spikes. Where are you making mechanical contact with something to provide those force impulses to the piezo transducer? I looked in your links, and did not see a datasheet for the piezo transducer that you want to use -- can you post a link to the datasheet? (sorry if I missed it)

I know the piezo is a very high voltage device

Only if the force impulses are really big, and even then the source impedance is very high. Simple voltage clamp diodes to the rails are generally enough to clip the voltage impulses from a piezo transducer.

 

[Rx7man]

I'm not sure which transducer to use at this point
Here's the reply from Maxim.. that last line is a little hard to english

 

[jrmichler]

Some comments:
My experience with piezoelectric transducers is that they need a charge amplifier (search the term) to properly interface with an A/D converter.

If you want to monitor pressure pulses in a diesel injection line, you will need a sample rate fast enough to capture the pulses. Figure on at least 5, and preferably 10, samples per pulse duration. And a processor fast enough to process the signal in between samples. You may also need an anti alias filter.

I did some tinkering with an Envirodiy Mayfly Arduino board: https://www.amazon.com/dp/B01F9B4WCG/?tag=pfamazon01-20. This board is designed for data acquisition. It comes with a real time clock, 10 bit and 16 bit A/D converters, multiple power supply options, and has a built in micro SD card slot. The A/D input impedance needs to be less 30K ohms for good accuracy and repeatability. I learned this after trying to measure an external battery voltage using a 1 Meg / 300K voltage divider. A 100K / 30K voltage divider worked well, while a 1 Meg / 300K divider had an unacceptable level of both random noise and bias error.

 

[Rx7man]

That's an interesting board, though I don't need to know the magnitude of the pulse, so there's got to be a way of doing this without an A/D converter and repeated sampling..

A charge amplifier may be necessary though, and will be kept in mind for sure