• Lithium iron phosphate (LiFePO4) battery test

    Michael Wen07/09/2016 at 14:27 0 comments

    I removed LDO from my NodeUSB (ESP8266) board, and use LiFePO4 battery to power it directly.

    700 mAh able to run about 6 hours (345 minutes):

    2016-07-08 13:04:30.324560

    2016-07-08 18:50:05.973346

    Then, I charged LiFePO4 battery (3.3V LDO directly) and ran another test:

    2016-07-08 23:40:50

    2016-07-09 01:15:34

    That is 95 minutes, so about 27% of capacity, 190 mAh.

    Second test is much batter (I charged longer this time, for 3 hours):

    2016-07-09 13:25:182016-07-09 16:07:58162 minutes

    That is about 47% of the capacity.

    If use 3.5V LDO to charge LiFePO4 battery, it can reach 95% of capacity. I will test it next week.

  • Lithium iron phosphate (LiFePO 4) battery

    Michael Wen07/08/2016 at 15:06 0 comments

    Today I started testing LiFePO4 battery. I had the idea of using LiFePO4 battery for few months. Now I just received the shipment early this week.

    Few benefits use LiFePO4 battery:

    1. Can use LiFePO4 battery directly power MCU, without LDO or buck converter. LiFePO4 battery discharge at 3.2V. This is huge for ultra-low power applications that average 3-15 uA. Even the really good LDO still consume 2-5 uA when MCU is sleep.
    2. Better high temperature performance.
    3. Long life, 2,000 charge/discharge cycles
    4. Large overcharge tolerance and safer performance
    5. Simplified battery management system and battery charger

  • First design

    Michael Wen07/07/2016 at 14:52 0 comments

    Here is the schematic of BeWi based on Atmega168 and NRF24l01+:

    1. Atmega168 read sensor data
    2. Atmega168 use SPI to talk to NRF24l01+ and send 2.4G BLE beacon packets
    3. Atmega168 control AO6604 to enable/disable battery charging.
    4. Atmega168 read battery voltage and decide when to charge, keep battery voltage low can greatly extend battery life
    5. HT7333 provide power to Atmega168 and NRF24l01+
    6. C2 is 0.22F super capacitor, depends on the setup, it can power BeWi alone with small solar module

  • Evaluate different chips/modules for WiFi, BLE beacons

    Michael Wen07/06/2016 at 19:14 0 comments

    After testing different chips/modules for WiFi, BLE beacons.

    I am leaning toward to use NRF24l01+ send and listen BLE beacon frames.

    The reasons:

    1. TI does not provide API to use CC2540/CC2541 in sniffer mode
    2. To write software on CC2540/CC2541, you need IAR, which cost $4,000 USD!
    3. ESP8266 chip use too much power, it is take too long to boot and transmit the packet, the best I can do is 200ms.

    Use another MCU (Arduino) with NRF24l01+ , anything can develop the firmware fairly easy. Cost will be low.