We are attempting to develop a low-power energy harvesting bluetooth sensing system using the CYBLE 214009-00 module. The system is designed to be powered with fuel cells, whose voltage is boosted with a boost converter chip, and the power is stored in a capacitor, which periodically discharges to intermittently power the BLE module to take measurements from sensors and broadcast them over bluetooth. More specifically, we first fully charge the capacitor (to around 4 V), then operate the BLE chip until the capacitor reaches 2.5 V, at which point we set the chip to go into deep sleep for a certain amount time and let the capacitor charge back up to full in this low power state. In between operation we would like the BLE chip to remain on in deep sleep mode since turning on the chip consumes lots of power and takes away from valuable that could be spent taking measurements, sending bluetooth packets etc. Thus, to find out how much power is required to keep the chip on in deep sleep, we programmed it to run in deep sleep, and powered our system with increasing amounts of power until we saw the capacitor voltage stabilize. We found that 5-6 mA at 0.6 V (3 mW) was required to keep the capacitor voltage constant, which is much more than we expect deep sleep to consume. Granted, there are other components on our board which take power or introduce inefficiency (instrumentation amps, voltage regulator, boost converter), but we still expect the system to run much more efficiently in deep sleep.
In order to more specifically test how much power the CYBLE chip itself was consuming, we ran the same deep sleep code on a CYBLE evaluation board while powering it with 3.3 V, and observed it to consume approximately 1.3 uA (4.3 uW).
In addition, we tried removing the CYBLE chip from the board and powering the remainder of the system with the power supply as before, and 1 mA was sufficient (which is much closer to what we expected to see from the previous test). Thus, we have reason to believe that somehow the connection of the chip to our board is introducing some severe inefficiencies, i.e. some of the chip's GPIOs are sinking current or are set to the wrong drive setting.
I have attached several files for reference:
DeepSleep.cydsn - PSOC 4 project intended to put the CYBLE chip in deep sleep indefinitely
wristband_pcb.pdf - PCB layout of the energy harvesting bluetooth sensing system, including the CYBLE chip.
wristband_schematic.pdf - schematic of above system
WristbandPCBV1.kicad_pcb - KiCad project included for more details
If anyone has any ideas or suggestions they would be greatly appreciated.