3G + Bluetooth 4.2 (BLE) + solar - advice need - Page 1
Forum section: electronics / projects

author: maestr0
author_rank: Newbie
timestamp: June 22, 2017, 02:32:26 am
content: My goal is to build a device that is able to download around 200kb of data (binary) from the Internet over 3G and upload it to another module (nRF52) over Bluetooth 4.2 (BLE) (encrypted). The device is going to be installed in a place without an access to a power source so it has to be powered from a solar panel. The device can be in a sleep mode for most of a day and wake up periodically every 30 min in order to check whether new commands have arrived over SMS. An SMS command can trigger an action on the device which can be a command to download a new binary data from the Interned from an API and upload this data to multiple client modules over BLE 4.2 via an encrypted channel. Once an upload is completed the device sleeps again.My current setup is as follow:- Adafruit FONA 3G Cellular + GPS Breakouthttps://learn.adafruit.com/adafruit-fona-3g-cellular-gps-breakout/overview- Arduino DUE- nRF52 module for BLE 4.2- large solar panel (there is no constraint on its size)- Super-Cap charged directly from the solar panel- buck-boost converter to power everything with 3.3VThe device has to survive -15C to +50C and is meant to stay outdoor for the entire year. New York City weather.The current setup works like this:Arduino DUE sleeps for 30 min (deep sleep -watchdog). When Arduino wakes up, it wakes up FONA 3G and initializes its network stack (GPRS) over Serial 1 port and downloads data from the Internet. Next, Arduino wakes up the nRF52 module, sends data to it over Serial 2. nRF52 receives data and sends it further over its Bluetooth BLE 4.2 (encrypted channel) to the other devices which are just nRF52 modules with BLE 4.2 and encryption enabled.This setup generally works but it requires a lot of power even if every component sleeps for most of the time. Would you recommend any other simpler solution? The key part is an ability to use BLE 4.2 with encryption.To sum up I need the device to1 - download 200kb from the internet on demand2 - connect to other devices over BLE with encryption and send downloaded dataIntel Edison and RPi3 are out of the equation due to a lack of support for BLE 4.2

author: poorchava
author_rank: Super Contributor
timestamp: June 22, 2017, 05:29:38 am
content: Cellular communication will use lot of current. At this point, it doesn't matter much how much current other stuff consumes i run mode, as it will still be way less than the GPRS module. Whetever it is that wakes the device up, should be powered directly from the battery/supercap not to waste energy on buck-boost. I'd try either some discrete circuit that generates pulses on a very long time base or some RTC chip that can be programmed to generate wakeup signals. This way you can literally cut all the power to the device off with a mosfet or something to reduce standby current to single microamp range.Another thing is charging - I'd strongly suggest using an MPPT chip to extract as much power from PV as possible. I recall low power single chip solutions from Rohm and IDT, but others major players have them as well for sure.And finally - you need to calculate the energy budget, accounting for all efficiencies, worst case active-on times and so on. If that comes up as negative, you are fucked anyways and simply need to use a bigger PV / energy storage.