i need a voltage sensor because i want to detect the voltage comming from the piezo from different pressures. so i want the exact number...
First, since 90V can kill your Arduino I'd recommend a pair of protection diodes* and a series resistor. (This circuit will knock-down the voltage in a non-linear fasion, so it's just protection against over-voltage... It is not used to attenuate a 0-90V signal down to 0-5V inearly... i.e. 90V or 45V would both read "5V".)Then, you'll need to measure the voltage output under your real-world conditions. You can experiment with a parallel resistor (probably in the in the megohm range) to knock-down the signal (linearly), if necessary. You are unlikely to get 90V and you might end-up getting less than 5V depending on your pressure & physical configuration. (But, I'd still recommend the protection diodes.) Or, you can use a regular 'ol voltage divider (again along with the protection diodes). But, with the high source impedance of piezo will create a 3-way voltage divider, and your signal will be reduced by more than the calculated amount... A lot more if you use low-value resistors in the voltage divider. Quotei need a voltage sensor because i want to detect the voltage comming from the piezo from different pressures. so i want the exact number...That's only gong to work for quick pressure CHANGES. A constant pressure (with no physical movement) is NOT going to generate a constant voltage.** I believe the piezo acts like a small capacitor, so it might sort-of hold the voltage for a several microseconds as it discharges through the load resistance.* The Arduino has built-in protection diodes, but they are rated for low current and are only there as a "last resort" in case something unexpected happens (such as static discharge). If you are experimenting with something that puts-out more than 5V in normal operation, you should take steps to reduce the voltage before it hits your Arduino. ** Conservation of energy... Gravity can generate electricity as water flows down and through a generator. But, you cannot use the static pressure of water behind a dam to generate electricity.
I am using those sensors in a reactive airsoft target system that I am building. The 1Mohm resistor in parallel that they suggest in the comment section works nicely. An analogRead on a good, solid hit gives a value between 500 and 750.
Quote from: wizdum on Jan 29, 2013, 03:25 amI am using those sensors in a reactive airsoft target system that I am building. The 1Mohm resistor in parallel that they suggest in the comment section works nicely. An analogRead on a good, solid hit gives a value between 500 and 750. Doesn't surprise me, the high source impedance that the device has would current limit well before the pin's built in positive and negative protection clamping diodes could fail. Lefty
500 to 700V?