Sunday, January 29, 2012
Piezoelectric bender used as a sensor and actuator
Piezoelectric benders are devices that have piezoelectric material on either side of a long flexible metal strip. When the material contracts on one side of the strip and expands on the other (eq due to applied voltage), the strip will bend. In many cases, one end of the strip will be fixed, and the free end will be allowed to deflect to move an object or provide force on an object. In this circuit, I sense the voltage generated when the bender is flexed, then send power to the bender via L6203 H-bridge drivers to effect movement in response. Thus, the bender functions as a sensor and an actuator in the same application. Instead of using a transmit/receive switch, I used a passive network of resistors and diodes to limit the voltage coming back from the bender. An ATMega8 microcontroller senses this limited voltage then controls the L6203's to cause the bender to move.
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2 comments:
Hi Ben,
First, thanks for your great vids...I check your blog almost daily and inevitably find something of common interest. You mentioned a while back about having a goal to affect education...well I for one have learned a few things from you!
I'd be curious about your sensing circuit and if it would work for very small movement of the strip. Or does your diode configuration sap off a small level of voltage? I like the idea of a micro controller doing the detection. I have pretty much the same project on the back burner and was planning to use some sort of triggering circuit set at a very low level. Needs to be both an amplifier and a buffer at the same time. I have not thought too much about it but if you have any insight I'd love to hear it.
john
simmers, you could definitely design a sense circuit that could detect very low voltage levels from the piezo bender. You basically want to amplify the signal (even with just unity gain) to prevent the signal from going negative or over the ADC's max input voltage. You could use an opamp that is known to be tolerant of input signals that are below gnd or far above Vcc. You could also use diodes or zener diodes to help take some of the stress off the opamp. You can sample with a microcontroller's ADC, or have a comparator trigger an interrupt. Good luck -Ben
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