Dear Forumites
I’m in the process of developing a semi-commercial SMS alarm, based on the Arduino UNO R3 and Sim800l. With semi-commercial I mean that these will be sold, but not in professional packaging or with any warranty, but I still need the hardware design to be sound, with an expected lifespan of more than two years. The coding is done.
It is with the hardware design that I need help. The module will be powered by anything between 12VDC (wall wart or car battery) and 50VDC (Solar panel).
First off, all hardware must be available on AliExpress. I think I need:
• a converter from 12-50VDC to 12V to power the Uno, the 12V -> 4.2 converter and the battery charger.
(50 - 12 VDC converter)
• a suitable battery pack. The battery will supply both the Uno and the Sim800L during a mains failure or, when the unit is powered by solar, throughout the night.
• A charging board for the 12V Li-ion battery
(charging board)
• A converter from 12VDC to 4.2VDC for the Sim800L (12 - 4.2VDC converter)
The unit will need a battery backup for at least 16 hours, with sufficient provision for at least 20 active SIM800L bursts, say one minute long each. I think this results in a battery capacity of
Sim800L standby: 4.2V * 7mA * 16 = 0.5Wh
Sim800L burst: 4.2V * 2A * 1 / 60 * 20 = 2.8Wh
UNO standby: 5V * 50mA * 16 = 4Wh
Indicating LED: 2.2V * 20mA * 16 = 0.7Wh
Total about 8Wh
Required for min 40% SOC = 12Wh. 3S1P 18650 batteries would work, and perhaps I could use the 12V charger of this offer as a wall-wart power supply?
Power supply battery
I need someone with experience with these boards/modules to advise me if I have selected the right ones, and if not, what I should choose instead.
I've posted the project on Freelancer, I think it should be easier to arrange for secure payment over there: