• Pressure Detection Circuit

    Bolzbrain • 05/10/2022 at 18:30 • 0 comments

    To sense the pressure i chose a small sensor:

    It has a range from 0-200g and a 8MR to 2kR resistance depending on the pressure.

    This datasheet here said it hat about 2.9kR when under 200g pressure.

    So i came up with a quit circuit based on a 741 op amp i had still around from another project:

    The circuit uses the 741 as comperator. R2 and R3 give me a reference voltage, R5 is sized it a way that together with R4 the voltage on in 3 will be higher than the reference voltage when more than 200g are on the sensor.

    Its a bit chaotic on the breadboard but i am happy it works, heres a first test:

    The LM741 isnt a very good choise for the long run tho.
    It needs at least 4.5V to work right....others make doe with 1.8V.

    It also isnt very good in therms of energy saving.
    If i realy wana make this device be powered with a supercap and not a battery i will need something like the MAX480CPA....

  • 160mV AC is still to low

    Bolzbrain • 05/07/2022 at 14:16 • 0 comments

    I tryed a few more magnet sizes for the linear generator

    I settled on magnets with 6mm diameter and 8mm lengh.

    A setup with 3 magnets and 3 coils gave me 160mV AC

  • shake generator first tests

    Bolzbrain • 04/26/2022 at 04:27 • 0 comments

    Linear shake generators have been around for a while, best example is the shake to load led lamp.

    I hope to scale down this principle.

    I choose to use cylindrical magnets with 3mm diameter and 3mm length.


    Now i was in need of a tube with 3mm inner diameter and wall as thin as possible.
    Every 10th of a millimeter more between the magnets and the coils would lower the generator.

    But where does one find a thin walled  tube?
    Well i tryed a few things like this pneumatic tubing with the lead of a thermocouple for a coil...

    This actually worked when i checked with the Multimeter in AC mode...i was geting around 0.12mV...still basically nothing but a start.

    Next step was to use another even thinner wire, so i took a old broken mini drone motor and stripped it of its windings.

    That allready looked a lot cleaner, but it didnt perform better.

    The walls of the pneumatic tube where just to thicc.

    Then it came to me, the nozzle diameter of my 3D printer is 0.4mm thats thin.

    So i printed a very thin pipe in vase mode, at first i had problems with cooling but then i just slowed down the print to 10% and it worked.

    That gave me some better results, but still way to little voltage to run anything usefull.

    I have to get above 20mV so i could use a LTC3108 energy harvesting IC to get some usefull voltage.

    Then i found out that by stacking a few coils in series i could get higher voltages, so i gave it a try (lighter for scale).

    I also printed a few washers to keep 3mm distance between the coils and a few tiny distance keepers for the magnets.

    This setup generates 100uA peaks in short circuit and about 10mV peaks without load.

    Thats still below the 20mV DC i need to reach...but a step in the right direction.


    I think i will just add more coils in series.

    Another idea would be to add 2x 1:100 SMD transformator.

    That would give me 1000mV peaks in theory. then i could add diodes and will be left with about 300mV pulsed DC.

    Slap a condensator behind that and the LTC3108...bam done.

  • Prototype 1

    Bolzbrain • 04/22/2022 at 00:15 • 0 comments

    I could not wait for the sensor to be shipped to i build a very rough first Prototype:

  • 3D Printing first parts

    Bolzbrain • 04/21/2022 at 20:12 • 0 comments

    First Prototype will use a spring and piston design that thriggers the indocator.

    Printing in Progress right now...

  • First steps

    Bolzbrain • 04/21/2022 at 17:39 • 0 comments

    I scoped out some out some pressure sensors, and then choose a

    20g-2 kg high precision resistance type thin film force sensor

    its a generic disk type sensor.


    After doing some research on "shake generators" i found that generators in the form factor (small) arent for sale sadly.

    So i am gona  build my own.

    But building a smal form factor shake generator is almost a own project.

    Thats why the first prototypes will use a button cell so i can test the rest of the sensors untill i get the generator working.

    I also started to design the handle in FreeCad