piezo-sensor
git.defproc.co.uk / DefProc
A conditioning circuit for using a piezo as an impact sensor for foam darts
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Digikey
Digikey
Mouser
Mouser
RS
RS
Newark
Newark
Farnell
Farnell

A standalone piezo conditioning board for use as an impact sensor.

The circuit takes the noisy input voltage signal from the attached piezo, rectifies it, clips it to 5V and passes through an RC pair to give a pulse-and-discharge signal.

The pulse duration is approximately 10ms long, and the maximum voltage relates to the impact size on the piezo, so it's only triggered by an impact and not a slow press.

By choosing a threshold voltage level on the attached device, it's possible to filter out impacts above a required size. The RC circuit is specifically sized to be useful for registering strikes from foam dart guns such as those from Nerf guns.

 
ReferencesQtyDescriptionManufacturerMPNDigikeyMouserRSNewarkFarnell
C114.7nF (any manufacturer)MCFU5472Z5BC1076CT-ND72152879411844
D1, D22Shottky Rectifier diodeSR110080505731861419
D315.1V Zener Diode1N751A1N751A CT-ND25083360601861484
P11
PZ1120mm uncased piezo (https://www.kitronik.co.uk/c3309-20mm-uncased-piezo.html)7BB-20-6L0490-7712-ND1192520
R111M 1/4W (any manufacturer)LR0204F1M0CF14JT1M00CT-ND47786622329894