u/Tiger_Impuls

Hi everyone,

Two friends of mine wanted to do their final high-school research project (PWS for the Dutch folks) on piezoelectric energy harvesting and the possibility of using the generated energy for real-world applications. I told them numerous times that the amount of energy generated by piezo elements is exceptionally low, but they still wanted to research the piezo effect

Their main goal is to investigate how much energy piezo elements can generate and compare different elements to see how properties such as diameter, excitation frequency, impedance, and capacitance influence the harvested energy. To give them a way to measure this, I decided to design a PCB for them.

The main measurement method uses a programmable capacitor bank. By measuring the voltage increase, they can calculate the stored energy. Making the capacitance programmable also allows them to analyse which capacitance is optimal for charge transfer and storage. By using both MLCCs and electrolytic capacitors, they can also analyse differences in leakage current.

Since they also wanted to learn how to use an oscilloscope, I added a parallel load resistor to the capacitor bank. This can be used to measure energy delivered to a resistive load, as well as to discharge the capacitor bank. With no capacitors connected, the same setup can also be used to measure the losses of the full-bridge rectifier.

The ADC has a VREF of 2.048 V, so a resistor divider scales the maximum 10 V input down to 2.032 V. We don't intend to charge the capacitors beyond 8 V. A MOSFET disconnects the ADC and resistor divider when they're not being measured to prevent continuously draining the capacitor bank.

The goal was to provide as many research possibilities as possible while keeping the cost relatively low. I know there are dedicated piezo energy-harvesting ICs, but they are relatively expensive and would give the students less opportunity to experiment with the individual components.

The PCB is 40mm in diameter to fit in a custom designed case with a load cell to be able to apply a constant bending force to the piezo elements. The case will also support the extending connectors.

Are there any problems or potential improvements you can see with this PCB or measurement approach?

All feedback is greatly appreciated!

P.S. Any recommendations for a budget-friendly buffer op-amp would also be appreciated.

[REVIEW REQUEST] Programmable capacitor bank for piezo energy harvesting experiments