5

I hope to use a piezoelectric button to harvest and produce a sufficient energy burst to power ON and bootup a MSP430 for a few ms enough to update a simple data structure (e.g. two integers stored in nonvolatile memory e.g. FRAM) and then power OFF. Note that the MCU will be completely dead before the piezo button press. This updated data structure will be used later on when sufficient energy is available to do more complex tasks (e.g. perform computation/send signal over wifi etc.).

Assume: The FRAM-range MSP430 (e.g. MSP430FR59xx) with lowest clock frequency (32kHz), min. operational voltage 1.8V, lowest power mode that can do the above operation. I'm not sure how much current the above operation (integer updating) would require, but I assume it's under 0.5mA, lasting for under 10ms. Assume there is another solar energy harvesting element that is charging up a secondary energy buffer (e.g. a largish capacitor) to do the complex MCU actions mentioned above.

I guess the objective is to see if there is a way to capture user input in a quick and dirty fashion and react upon the input later, when sufficient energy is available from the secondary energy source.

Questions:

  1. Can a piezoelectric sensor button or a capacitive touch sensor button produce enough energy to perform the above?

  2. Assuming (1) is possible and there are 2 such buttons (A and B), then can the MCU obtain knowledge of which button was pressed and gave it power?

winny
  • 13,064
  • 6
  • 46
  • 63
bd3lk
  • 63
  • 5
  • You tagged this "energy harvesting", are you wanting to derive power from the button, or just wake up the processor from a battery? – Ron Beyer May 02 '19 at 03:00
  • 5
    @RonBeyer It seems pretty clear that Rosh wants to power it from the button. – user253751 May 02 '19 at 03:02
  • @immibis Probably but I just don't see a single button press providing enough power for an microcontroller, unless they were pushing the button over and over to charge something that then ran the microcontroller. The MSP430 is a low-power device, but not that low... – Ron Beyer May 02 '19 at 03:21
  • 3
    @RonBeyer That's what they are asking. If the only thing it does is powers on, increases a counter by one and then turns off, would a piezo crystal or other energy harvesting method be enough? If you have some evidence that its not, then you should put that in an answer. – Passerby May 02 '19 at 03:36
  • Welcome to EE.SE! Keep in mind that *"Is it possible ...?"* is a yes/no question. If you're asking us to work it out for you, that would be too broad. You would need to specify something about what you ultimately want to accomplish and what constraints you have on the implementation. There are many different kinds of "nonvolatile memory", and you've left out any mention of how you expect to read that value later. You need to pick a technology, write the code, and then see whether you've got the energy to complete the task. What is your specific question? – Dave Tweed May 02 '19 at 03:48
  • Working with a guy who monitors the Piezo output from various strength taps. He sees upwards of 20 volts across 0.03uF piezo capacitance. That is 0.5 * 20 * 20 * 0.03uF = 0.5 * 400 * 3e-8 joules = 600e-8 joules or 6 microJoules. – analogsystemsrf May 02 '19 at 04:00
  • You need to specify what MSP430 you are working with, the clock frequency and supply voltage to get any real advice. The MSP430 active range use from about 100uA to 4mA depending on what you are doing. I seriously doubt you can make a Piezo device work, but you might be able to use a magnetic push-button. eg. Push a magnet through a coil and have a spring push it back. That way you harvest on the press and release. – Jack Creasey May 02 '19 at 05:44
  • @DaveTweed - I have updated the question. assume there is another energy source that's charging a cap to perform the more complex tasks. I'm asking this question in case someone is familiar with the piezo power output and msp430 energy consumption (before I go buy the items, want to see if the idea is feasible, and what design points are missing from the above) – bd3lk May 02 '19 at 06:15
  • 1) it will be a **huge challenge** to construct something that will use the energy of a button press to do something useful in a microC. The amount of energy from a normal button press is simply too low. 2) There are conventional ways of powering a microC, a small battery can last a year and a larger battery much longer. A small solar panel in combination with a rechargeable battery can last for years. – Bimpelrekkie May 02 '19 at 06:50
  • 3) This "energy harvesting" is a hype but **BE REALISTIC** and don't fall in the trap of trying to make a solution that is actually worse than current solutions. Example: a thermal energy powered watch. See it debunked by EEVBlog Dave here: https://www.youtube.com/watch?v=y4OeOQtiW0w&t=764s – Bimpelrekkie May 02 '19 at 06:51
  • @JackCreasey - Is there a magnetic push button that can be bought off the shelf , or would I need to construct one myself ? – bd3lk May 02 '19 at 08:28
  • 1
    @Bimpelrekkie - I understand that it is trivial to power a MCU using a solar panel and rechargeable battery, but i'm interested in a battery-less design. Not looking to replace existing solutions, but simply exploring options. – bd3lk May 02 '19 at 08:33
  • 1
    How much work are you willing to require the user to do? I can imagine an industrial-size pushbutton that requires 1 N of force and 1 cm of travel to activate. That's 10 mJ of work on the part of the user. If you can capture 10% of that energy (spin a small PM generator?), that's 1 mJ, or maybe 1 mA @ 2V for 0.5 s, which should be more than enough to do what you've outlined. – Dave Tweed May 02 '19 at 12:23
  • microcontrolled knetic energy harvesting solutions already exist and are starting to be "common", like this company: https://www.enocean.com/ Or this product : https://www.allocacoc.com/Home/Home/Product/detail/product_id/92 (which the remote control also works on knetic energy harvesting) There's also these modules: https://switches-sensors.zf.com/product/energy-harvesting-product-range/ – Gustavo Laureano May 02 '19 at 12:35
  • 1
    @Rosh There is a magnetic module produced by Enocean: http://www.farnell.com/datasheets/1637003.pdf?_ga=2.247993607.1014318034.1556808299-1576512398.1556808299 – Jack Creasey May 02 '19 at 15:06
  • @Bimpelrekkie If a normal button press doesn't have enough energy, I'm sure it's not out of the question to use a bigger, tougher button or an even lower-power microcontroller. – user253751 May 02 '19 at 21:55

0 Answers0