Hello guys, I'm building a disdrometer for my weather station project. I'm currently using a piezo speaker from an old radio mounted on a cd (small type) disc to increase it's sensitivity. When rain hits the surface, the transducer gives some output.

I got no pictures yet, but I'll post it later.
I've checked the output from a scope, and to put simply: If I tap gently on the cd platter, the output goes to around 100mV in a flash, and for a stronger one (that I render would be equivalent to a large raindrop) is around 2V.

Question:
1. I don't know if the scope is not good, but is the output too big for a small piezo transducer? It's just around 4.5 cm in diameter.
2. I'm planning to use an LM386 to amplify the readings up to 5V max (to be fed into a PIC18F) so before I do that is that okay? Or are there better parts to use?

Thanks to John (jpanhalt) who suggested using SoundRuler to analyze the readings.
Here's the link to a less defined project: http://www.instructables.com/id/Make...e-disdrometer/
Cheers.

A very large raindrop or hail will cause the output voltage of the piezo transducer to be so high that it damages the input of the amplifier.
Look at an Electronic Drums circuit that uses a zener diode to clamp the piezo transducer's output voltage to a reasonable level.

Wow. Piezo's output can be that high? It's a wonder how something that small could produce so much output.
So basically the coupling is ac? What's wrong with dc?
....And lastly, is an LM386 a good substitute for the LM324?

...And the terminals of the piezo transducer is connected to the JACK NC, eh?.

Originally Posted by Vizier87

Wow. Piezo's output can be that high? It's a wonder how something that small could produce so much output.

Guess what is inside an electonic lighter? A tiny piezo transducer that is hit with a tiny hammer to make a spark with thousands of volts.

So basically the coupling is ac? What's wrong with dc?

A piezo is a capacitor. It does not produce DC and it does not pass DC. so the couplung capacitor is not required.

....And lastly, is an LM386 a good substitute for the LM324?

An LM386 is a power amplifier with its inputs biased and with internal negative feedback for a gain of 20 which is too high. If you add more negative feedback then it will oscillate.

Use an LM358 which is a dual opamp in an 8-pins case. Its opamps are the same as the ones in an LM324 quad opamp.

Here's my disdrometer:

http://www.electro-tech-online.com/a...1&d=1256395909

Now I'm wondering: The output observed from the scope is bipolar,but the reference for the LM358 is gonna be 5V to GND, which means I can't see anything under the 0V region. Is there a way so that the negative output can be included into the positive signal output?

And...thanks for the schematic. How does the zener really function anyway?

Resolved: The schottky diode
I'm currently working on how to transmit readings so that a software (preferably MATLAB) can 'hear' the raindrops on the disdrometer.

The system's like this:
A PIC activates direct transmission from the disdrometer output so that a receiver 'hears' the output to be analyzed using a MATLAB-based software, SoundRuler. Data transmission is via a 315 Mhz RF module, half duplex communication and another PIC circuit also has the RF module pair to receive the 'raindrops', connected to a PC/laptop to process the data.
Can MATLAB process direct communication with PICs which are USB connected to a PC?