HCD Pin not working on hw version 0.3 on C module

The pin just floats: never gets driven when trying to use buzzer or haptic.  This did work in version 0.2.  GPIO's seem to work fine.


  • I've let the firmware developer know of the issue.
  • @KingTalullah

    I have a MetaWearC r0.3 device set up in the lab running the latest release firmware and it is generating the HCD signal as expected.

    Could you provide more details about how you are testing -- what is connected to the pin, which app you are using, etc?
  • I've tried connecting both the piezo speaker and the coin battery to the 0.3, both of which work on the 0.2.  I've also tested with a multi-meter and the HCD pin just floats.  On the 0.2, I see 3V across.
  • I'm using the mbientlab app.
  • edited June 2016
    @KingTalullah The HCD driver is setup as "open-drain" and only provides a pull down to sink the current of an attached high current peripheral.  In order to drive a piezo buzzer, an additional resistor needs to be added in parallel with the buzzer to provide the 3V to drive it.  We add this resistor, which needs a value of 1k ohm, to the boards ordered with a piezo before we ship them.  Here is the circuit diagram from the product sheet, as well as a shot of the board showing where the 1k R4 can be added.


  • Ah, I had a feeling I was missing something.  Thanks for the instructions.  I will take care of it.
This discussion has been closed.