Powering an iComSat GSM Shield and a Gear Motor with LiPo Battery

Question

I have an iComSat GSM Arduino Shield (based on the sim900) and a gear motor that I am planning on using with a Teensy 3.1 microcontroller. I'd like to power the whole rig using a 2000mAh LiPo Battery Cell.

So I have:

• Teensy microcontroller Vin= 3.4 - 4.5V
• GSM Shield __ | Vin=9-20V _ Iavg=500mA _ Ipulse=2000mA
• Gear Motor __ | Vin=6V _ Ifree=70mA _ Istall=1600mA
• LiPo Battery Pack __ | V=3.3 - 4.3 V _ Imax = 2C = 4000mA

My question is which of the following courses of action should I take, and are there alternative courses of action that I haven't thought of yet?

1. Use boosting circuits to boost the battery voltage up to 6 V and 15 V for the gear motor and the GSM module, respectively

2. Use a higher voltage battery source (i.e. 12 or 15V) and use voltage reduction circuits to limit the voltage seen by the servo and microcontroller.

3. Get a sim 900 GSM module on its own (i.e. not integrated into an Arduino Shield) and use it directly with the battery (the sim900 on its own needs 3.2 - 4.8 V). I would still use a boosting circuit for the gear motor.

What's the most energy efficient and robust solution? Or is there another solution I haven't though of?

Answer 1

The GSM shield looks to pass the input directly to a LDO, and regulate it down to 3.8V? I’ve no idea why they claim such a high input voltage requirement, I could be missing something.

With care you could patch the VIN & VBAT leads together on the module, and power them both from 3.8V. The LDO should drop itself out of the circuit, although check it’s not getting hot (e.g. dissipating any power). That device doesn’t explicitly state it can be back-powered like some LDOs will, but if you tie VIN & VOUT together it should prevent damage.

No promises though, if you break anything taking my advice I’m not liable!

But this would leave you with all logic powered @ a lower voltage.