SUN : Self-Sustained Ultralow-power Node

Ambient/Solar Energy harvesting based nodes that DON'T run on a LiPo battery.

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Challenge it addresses: It is expected that by 2020, 50 billion devices will be connected to the internet. An important consideration for a lot of those devices that don’t need a lot of computation power or, that only sense the environment and transmit that data for processing, is of power consumption. LiPo batteries can no longer be used because it may be possible to replace 100 batteries, it’s not possible to replace 1,00,000 LiPo cells (for devices in large sensor networks). This project attempts to develop a node that uses Solar Energy and(or) Ambient light harvesting to power an ultra-low power node.

Simply Put: I want to show that it is possible to keep running a system on a supercapacitor for at least 24 hours. I am using (BLE) CC2650 uC (will be replaced by CC1350 dual band uC), that runs a RTOS and has a special 16 bit core called "Sensor Controller". Through optimized firmware, hardware and negative feedback i want to design a complete solution.

I have already made a working prototype. I will upload the details about it slowly. Right now here are some videos showing the prototype in action. The processor is ARM Cortex M3+, CC2650 from Texas Instruments. It is running a RTOS. One novel feature of CC2650 is the "Sensor Controller Core" which is a separate 16 bit core. It is optimized for extremely low power and autonomous operation form the rest of the core that can sleep. Here the Sensor Controller reads the Ambient light sensor OPT3001 via I2C and if the value is beyond a maximum value or below a minimum value then it glows an LED to notify that. (NOTE: Glowing LEDs to indicate that is really bad, because the whole system without the LED uses less than 1mA with non optimized code , but the LED itself consumes around 4mA !!. This was just for demonstration purposes.)

In the final prototype CC2650 will be replaced by CC1350. I had started this project before CC1350 was launched, hence i am still developing on CC2650. But the RTOS that runs is exactly the same, hence in the last prototype the changes to the code would be minimal. CC1350 is a SoC which has BOTH SubGHz and BLE. So majority of the nodes will use SubGHz for data transmission, but the central node would use both.

Here is a video of the same setup in action with some explanation and showing the supercapacitor charging under ambient light.

Before programming and everything i tested the Power Management circuit. Although i had worked before with BQ25570 and BQ25505 so i knew how to deal with them but it was still necessary to test every detail thoroughly. So here is a video that has 2 tests, one on a sunny day and the other on a cloudy day. To show that the Energy Harvesting circuit is working i replaced the Ferrite Bead with a LED in series with a resistor. Whenever the supercapacitor charges to a pre-programmed level (resistor programming of BQ25570) then the internal mosfet in BQ25570 turns ON the buck converter that produces a constant 1.9V from the linearly decreasing voltage of the Supercapacitor.


Layout, top layer

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Layout, Bottom layer

Portable Network Graphics (PNG) - 386.62 kB - 03/29/2017 at 03:56

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Portable Network Graphics (PNG) - 376.48 kB - 03/27/2017 at 12:44

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  • 1 × CC2650MODA BLE Module from Texas Instruments
  • 1 × BQ25570 Energy Harvestinng IC from Texas Instruments
  • 1 × OPT3001 Ambient Light Sensor
  • 1 × TMP112 Temperature Sensor
  • 1 × AVX Supercapacitor 22mF BZ054B223ZS Best Cap series supercapacitor from AVX. Very low leakage caps.
  • 1 × SLMD121H09L Solar Panel from IXYS

  • Comparing Supercapacitor with Small Energy Devices from Murata

    Shantam Raj04/03/2017 at 17:51 4 comments

    Recently Murata Launched a new line of products called "Small Energy Devices". You can read about them here. Basically it's a miniature device with a high energy storage capacity, low ESR, fast charging and discharging and the ability to withstand load fluctuations. It may be used as a secondary battery in the same way as a capacitor. This energy device achieves better charge/discharge characteristics and has an extended service life superior to conventional batteries. Well suited as a power supply for wearable devices or sensor nodes for wireless sensor networks, this device maintains flat voltage characteristics while accommodating a wide range of load characteristics.



    Their benefits are -

    I have placed order for the UMAC (the top one) series and will design the PCBs accordingly.

  • Voltage Feedback

    Shantam Raj03/24/2017 at 08:52 0 comments

    Currently there is no feedback in the system. I have already started designing a PCB which has feedback. Basically the idea is to monitor the VBAT (Supercapacitor voltage) and the VSTOR(Boost regulator o/p from BQ25570) pins via Analog pins.

    I have also changed the placement of the sensors from the components side to the Solar Panel side as when it will be deployed in the fields then the solar panels will be on top and the sensors need to make measurements in that orientation. Here is how they look like (need to complete s bit of routing )

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