circuit description integrated electronic piezo electric (iepe) type sensors require a constant current source for proper operation. various methods can be used to provide constant current. the circuit below is recommended to provide 4 ma constant current at room temperature for powering iepe sensors. the capacitor at “sensor +” ac coupled the output signal, blocking the dc voltage. the current temperature coefficient is about to 0.25%/deg c.
parts list t1 ａnd t2 can be most of pnp type transistor, such as 3906, 9012 etc.
r1, 165 ohm, sets the constant current level, decreasing the value will increase the current, and vice versa.
r2, 51k ohm typical. precision is not important.