Arduino based SmartPort voltage meter

LiPo Voltage metering with Arduino

DIY lipo voltage checker (arduino) - YouTube
1S-6S Battery Voltage Monitor (ROS) : 7 Steps (with Pictures) - Instructables
www.iforce2d.net/sketches/VoltageChecker.ino

Arduino SmartPort

marhar/arduino-frskysp: FrSky SmartPort protocol library for Arduino
arduino-frskysp/FrskySP_sensor_demo.ino at master · marhar/arduino-frskysp
FrskySP: Main Page
FrSky S-Port telemetry library - easy to use and configurable - RC Groups
Google Code Archive - Long-term storage for Google Code Project Hosting.

This seems the best one:
Dakkaron/MinimalSPORTVoltmeter: Arduino Voltmeter compatible to FrSky SPort Telemetry with minimal additional hardware

Install Notes for Dakkaron FrSkySportTelemetry

#install FrSkySportTelemetry
cd arduino lib directory
git@github.com:marhar/FrSkySportTelemetry.git

# install Dakkaron
cd github place
git clone git@github.com:marhar/MinimalSPORTVoltmeter.git

Details on Maximum Current

Mike Blandford responds to my query:

I'd use 5V as the maximum for the SPort signal, assuming you are using standard FrSky hardware. The SPort input is via a transistor buffer with a 1K resistor in series with the base.

The SPort output is driven by a SN74LVC1G126 powered from 3.3V. When not driving the SPort signal, this has an absolute maximum voltage rating of 6.5V. 

When driving the bus, the voltage rating is (VCC+0.5) so 3.8V. 

However, the output signal passes through a 51 ohm resistor, so as long as the current is limited to 50mA the device is safe. 50mA through 51 ohms is 2.55V, so the limit is 3.8+2.55 = 6.35V. 

All values taken from the TI datasheet for the SN74LVC1G126.

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