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# Help with piezoelectric circuit

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I connected three piezoelectric sensors to a rectifier which was further connected to a capacitor (100µF). I kept hitting the sensors for some time, and measured the voltage across the capacitor using a multi-meter. It displayed the voltage to be around 6 volts. Then, I used a breadboard to connect the capacitor, a resistor (100Ω ± 5%) and an LED bulb. The bulb didn’t light up even for a fraction of a second. I measured the voltage across the capacitor again and found out that it had been discharged.

Any suggestions on how I can fix this?ledcapacitorpiezoelectricitypiezoelectric-effectShareEditFollowFlagasked 1 hour agoMr.Brawler111 bronze badge New contributor

• how to fix what? – jsotola 1 hour ago
• What you have learned is that a 100uF capacitor doesn’t store a lot of charge, and a piezoelectric sensor doesn’t generate a lot of current/power. So if you want more usable amounts of electricity, you could connect hundreds of piezos to something that constantly vibrates and power a few small LEDs that way. What are you hoping for? If you want to make a light light up on impact you can amplify the signal from the sensor. Generating power with a piezo is more of a problem or it would be commonly done. – K H 50 mins ago
• Ah, you are telling us too many things at a time. Me IQ97 lost count at three. Now I suggest to eat the big elephant byte by byte in three or four bytes, starting the with the piezo. (1) So you hit the poor little piezo sensor with a hammer, and the piezo gets excited, generating electrons like a charged up capacitor. (2) Now the charged up piezo, say negative end, is connected to a capacitor through a rectifier, which lets electrons pass through but not allow them go back. (3) Now you use a multimeter and finds the capacitor charged up to 6V. So far so good eh? / to continue, … – tlfong01 43 mins ago
• (4) Now let us look at the cap. If I remember correctly, the cap, after collecting the electrons (charges), should have an energy of 1/2 * (C * (V** 2)).= (100 * 10**-6) * (6V * 6V) (my always dodgy calculation is not proofread. :)) = (100 * 6 * 6 * 6) * (10**-6) ~= 21,000 micro Joule. (5) Now you connect the cap to a LED, which our stupid human eyes should see it growing red, if there is, say, current of 5mA, passing through it. (6) Now the starting discharging current should be big, something like V/R, where V = 6V, and R the “initial” resistance of the LED. / to continue, … – tlfong01 21 mins ago
• (7) If the initial resistance R of the LED is too big, then the current passing through, by Ohme’s Law, I = V/R might be smaller than 5mA, so the LED wount bother to light up. (8) And even the initial current is bigger than 5mA, the cap might run out of steam, I mean, electrons very soon, perhaps in 10 micro seconds. In other words, even the LED lights up for 10uS, how can we stupid eyes notice any flick of light so smaller than 1/25 second? So my answer to your question is that my/your stupid human eyes are so very slow to see anything. / to continue, … – tlfong01 12 mins ago
• (8) There are a couple of workarounds:(a) use a tight string, say guitar string to hit the piezo, then you might see LED blinking, as the string repeatedly hitting the piezo, refilling it with new electrons. (9) Use a digital storage oscilloscope, eg my Rigol DS1064, 50MHz, 1G samples per second, to store the cap discharge waveform, and display back in slow motion. (10) Actually I did this piezo hitting, current storing/displaying game a while ago. Perhaps I should search my lab log and show you. Ah locking down supper time. See you late this evening or tomorrow. – tlfong01 20 secs ago   Edit

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