Piezo n Solar

Discussion in 'The Projects Forum' started by havish, Nov 4, 2010.

  1. havish

    Thread Starter New Member

    Nov 4, 2010

    My team is working on a walking charger project with peizo electric sensors and solar panels.

    we are using PIC12F683 micro and we connect a diode to the solar as 1 input and we connect Piezo to a harvesting energy module as 2 Input, so input1,2 goes to micro, and micro compares whichever input has greater voltage, takes that voltage and sends it to MAX666 and further to Lithium ion rechargeable batteries for them to charge. At the same, we use LM35 temp sensor to monitor the batteries, if they are heat/temp goes up, the temp sensor acts as third input to the micro and shutdowns the charging functionality.

    The problem is, we drew the circuit on a paper and asked a guy for help to design the circuit, but he added relay switches and other transistors etc.. into our design and we're not sure, if that is correct. would you please take a look and explain / tell if the work is done right?

    thank you in advance.
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    Hope you didn't pay for that.
    Some notes:
    You need at least 2.5V between VREF and GND (check the datasheet as this may vary for the 12F683 but 1.2V seems too low.
    Add a small 0.1uF cap to VREF and GND
    Do you need an accurate VREF as you've already got a regulated supply. Should be enough for simple temperature monitoring.
    NPN as a high side driver? just unusual as PNP is the norm for a high side driver.
    Use a bigger PIC and latching relays (you'll need the extra I/O to drive a latching relay)
    Can you find a solid state solution vs relays? A P-channel power MOSFET maybe...
    Why are you switching between two power sources? Can't you just combine them or use blocking diodes (higher voltage automatically wins)
    Standard mistake is avoiding decoupling caps.

    How much does your peizo generate?
  3. havish

    Thread Starter New Member

    Nov 4, 2010
    thanks for the reply.

    I have another quesiton, can we directly connect the power inputs to the PIC12F683 micro and get a power output? that way, we dont need a relay

    thank you
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    depends. do you mean charge a battery with the pin out of the micro direct?

    again depends upon the battery resistance.

    Would I DEPEND on that configuration to operate when I needed it most? Probably not.