FRDM-KL25Z battery power problem

[bobalong]

My project is a simple timestamp logger.  I'm using a FRDM-KL25Z with  a DS3231 I2C clock module, and 2 buttons with 22K pullups.  I assume I have a Rev-D board since there is no provision on board for a 5v regulator and associated caps.

It works well when connected to my PC using the KL25Z-USB connector, but not when using the other supply options.  I have tried regulated 5v on VIN and regulated 3.3 v on the 3.3v pin.  The program does not work with either.  Both behave the same as when I use the OpenSDA connector ( which I know does not allow the program to run).  I have not tried attaching a coin cell yet.

How do I power the project with a battery?

[bobalong · Accepted solution]

I was barking up  the wrong tree!  It was a USB issue, not power.

The project is a pocket-size device that will log the time each time a button is pressed.  At the end of the day it will bit connected via USB to my PC to upload the results.

I had the USBKeyboard declaration at the top of the code, so the USB initialisation occurred long before it was needed.

I moved it into the function that does the transfer with a 2 second delay after it and the project works as intended.

[BlackNight]

Hi James,

the usual way is to connect your battery to V_IN. This is what I'm using (see 5V Generation from V_IN on the Freedom Board RevE | MCU on Eclipse ). However, if you need 5V on the 5V header, then you need to add a DC-DC converter (see that article) to generate 5V from V_IN, as this is otherwise generated from the USB connector (check the board schematics).

I assume that you have your DS3231 (or 3232?) powered by 3.3V, so you should be fine. But if you have other (off-board) peripherals, you need to generate that 5V from the battery somehow.

I hope this helps,

Erich

[bobalong]

Unfortunately, no help.  I do not need 5v, only 3.3v.  The only reason I tried 5v was to see if it would work.

As I said before, connecting the proper voltage supply to the VIN and 3.3v pins does not work.  I have tried with 2 boards with the same result.

Any clues on where to get a coin-cell holder for the board?  All the ones I've seen do not have compatible pins.

[BlackNight]

Hi James,

I suggest you check the schematics as it could be that you have damaged the DC-DC converters somehow? Follow the path on the schematics and check if the parts have the proper voltage.

As for the con cell holder: Completing the FRDM-KL25Z Board | MCU on Eclipse

Erich

[bobalong]

Curioser and curioser.  Since the board works with the KL25Z-USB connection the DC-DC converter is working.  Also, the 3.3v input bypasses the converter.  I tried powering the board using a USB charger and the KL25Z-USB connection.  No Luck!  It appears that the USB library I'm using may be the problem.  If it cannot initialise, it hangs.  I think.  I'm using the online mbed IDE.