This simple high impedance amplifier is suited to boost the output signal of a piezo-disk making it to a microphone, geophone, hydrophone or use it as accelerometer sensor. Mounting the piezo with double-faced adhesive tape to a wall, structure-borne sound can be captured. Further experimenting with other objects will reveal lots of surprising sounds.
A breadboard version is quickly assembled when wire connections are following the red traces on the solder-side of the board. The double-sided PCB layout can be found in the zip file.
puttings things together
To minimize hum or other electrical noise you should use shielded cable to connect the piezo-disk.
The shield is connected to -IN and to the outer metal rim of the piezo-disk. Also putting the amplifier into a metal can ( Fishermans ) will reduce the 50/60 Hz hum a lot. Two AAA batteries as supply will last about 1000 hours and have the advantage that they have less noise than an DC adapter. To run the circuit with 9 Volt bock batterie is are also possible.
Choosing the right value for resistor R1
When you want to capture sub-audio signals or you want to use the piezo as an accelerometer a 10 Meg resistor allows a low frequency range. However when the amp is switched on or a strong signal through dangling the piezo it will take a while until the amp is settled again. Reducing R1 to 100K or 10K this effect will disappear but the frequency range rises more.
R1= 10..1 M ; sub-audio, accelerometer
R1= 100..10K; audio, voices, music
Cotton Wool Video
Force Sensor / Accelerometer
Here the piezo-disk acts as a accelerometer/force sensor. The video shows that even slow movements are easily registerd.
Piezo Force Videohttp://interface.khm.de/wp-content/uploads/2012/01/PiezoPreamp_force.flv
Piezo Preamp V3 Eagle PCB
PiezoPreampV3 Eagle board files 9/2012
Martin Nawrath, firstname.lastname@example.org