BC127 no life at all


This is my first post here but i have been in electronics for 40+ years. I recently purchased a BC127 module and am trying to get it working or at least showing some signs of life. Using the BC127 datasheet pin-out I have soldered 36awg wire-wrap wire directly to the pins to get the module to work with breadboards. Pins 1, 2, 3 ,4, 11, 22, 27 are all wired to ground. Pins 33, 34 are 3.3v dc. Pins 37, 38, 39 are connected to 3 leds, red, blue and green respectively with a 240 ohm resistor in series with each. The LEDS have common anodes connected to 3.3v. Finally GND and pins 41, 42 are connected to a FTDI USB to usart link to the comp. All wiring/soldering has been inspected using 200X microscope and all have been checked for continuity and non are shorted to gnd or any other pin. When i supply 3.3v to pins 33, 34 I expected some LED activity but there is no life from the module. I have confirmed the module is getting proper power. Monitoring the LED open drain outputs they are staying in the high impedance state so i am assuming the module is not running it’s firmware. Is there another pin that should be connected to get some life from the module. I have been in electronics for many years so i am seasoned at soldering, testing, and diagnosing ccts but this thing is doing nothing.
Any help would be most appreciated thank you.


I should add that the reset pin is not connected. The eval board shows a 10K res to V+ 3.3v but measuring at the rst pin it is already at V+ 3.3v so i am assuming there is an internal pull-up res.
Non of the battery pins are connected. vbat, vbat sense, vchg, chg ext, and vregen have all been left disconnected.
For now:
gnds, vdd pads (power)
LEDs 1, 2, 3, and 3.3v (indication)
TX, RX, and gnd (communication)
are all i have connected.


Hi Laurie,

Have a look at page 28 at the product technical specification:

Full PDF can be found at:

If you power up correctly, the BC127 will print some info to your terminal after powering up (version etc.)

Good luck!


I am not using the battery at all. Power is from an external linear power supply. There is no CPU in charge of the power up sequence. Just the raw BC127 itself. I guess i should be asking which pins need to be powered and which i can leave alone. I appreciate the quick response but it adds to my confusion as it assumes a battery will be in the picture. There is no battery.


Thank you Dave. The module came from Sparkfun which backs up to Blue Creations, which backs up to Sierra and neither of the two doc’s nor the sch’s clearly show which pins necessarily need to be connected to V+ for proper power-up. Only pin 33 (VDD PADS = Positive Supply Input) and pin 34 (3V3_USB = Positive Supply input). Pins 28, 29, 30, 31, and 32 are indicated to be necessary for battery operation which i am not needing as yet.
The manual you suggested shows a different layout for external power operation so I am getting the microscope and needle tipped iron ready. I’ll let you know what happens.
Since I have just discovered Sierra, it looks like i have a treasure trove of info and a great bunch of people to get to know.


OK I am up and running. Leds flashing and the link to terminal emulator is working as well. Thanks again.


Well done and good luck! :slight_smile:


Hello, I am in the same situation as you, I need to run the BC127 but without a battery. Would you mind telling me which of the power pins you left unconnected?