I am designing a piezo energy harvesting board with some built-in features like a fuel gauge you can connect to a MCU to get readings on the battery.
So, on particular application I can image this being used is: you have the module strapped to your leg (around the calf area) on one side then the battery on the other side or something like that. Then, there are leads that go into the shoe with the piezo cell like this AB2063B-2.
The leads will also likely go to a vibration sensor like LDT0-028K. My thing now is how do I interface with this sensor to have connections to a MCU?
I've seen articles like this or this arduino forum thread saying to use like a 1M - 50MΩ depending on frequency. From google, frequency of someone running or jogging is like 2 - 3 Hz?
From the Arduino thread, that implies needing like 20MΩ for the load. But the commenter also mentioned using a force sense resistor if you want to measure pressure or bend ratio. So, I looked it up and the force sense resistors look like the vibration sensors or piezo sense transducers so I don't really understand where it is meant to go.
Also, after the load resistor, what connections do you need for the MCU? An analog pin and GND? Does it matter which is which?
the last time I implemented a wearable device I used a PIC24FJ256GA705 microcontroller with a LSM9DS1_magnetometer to sense user movement and a BM71 BLE module to send results to a smartphone
these days I would use a small ESP32 microcontroller - has plenty of memory (for a microcontroller) GPIO, ADC/DAC, SPI/I2C/Canbus interfaces, WiFi and BLE, e.g. ESP32-S3 Super Mini
The way the forum works is you post a hand drawn wiring diagram and link any non-common parts datasheet. You also post your Auto-formatted code in a < CODE/ > block. If it's a lot of code trim out code that does NOT change the erroneous behaviour. Also any output also posted in a code bock.
There’s no code for this and I posted an example of the wiring that I think it might look like but ultimately, the wiring and connections and how to set it up is my question
Oh thank you for that. I’m using LTC4070 as the medium to use piezo (converted to DC) to charge a li-ion battery. The ranges of resonant frequency I’ve seen for piezo cells on digikey are commonly about 6kHz - 30kHz. I’m not sure the exact cell a user would want to use
So in my example, I’m thinking maybe the user attaches an sd card module to store data taken. I’m trying to capture the most common / useful measurements from someone walking or running or jogging or common situations one would use a piezo cell.
I connected a buck-boost directly to the battery since the idea is to have the battery primarily powering the load and have the piezo trickle charge it. I’d anticipate max current to typically be 500mA, especially if the storage of measurements is through the air like WiFi or bluetooth
I have a few of these sensors and I don't remember using a load resistor at all. I probably had a diode (1N914) reverse biased to Vcc to handle the overvoltage, though.
If they bend at the same rate and time, and if... the polarity is the same.
My experience is that polarity can differ between two piezos of the same batch.
And the chemical makup and shape of the piezo as well as the mechanical coupling to the piezo will have to be experimentally determined. All piezo material is not the same.
The shoe is just an example I came up with, a user can use this for anything they choose.
My main issue is I don't understand how to set up a vibration sensor to give outputs that you can connect to a MCU like arduino, y'all think I should add an accelerometer too?
The problem to solve is the sensor produces high voltage AC and the Arduino can only measure low voltage DC. Doesn't that tell you you need to begin by measuring the sensor output and then rectify that to a DC? Measure that and use resistors to make a voltage divider circuit to reduce the voltage to some value the Arduino can use.
