A hand-held display for the mobile logger

A hand-held display for the mobile logger

Although the Logger works fine in our 2014 Chevy Impala, its dash is not suitable for supporting it. This handy accessory lets the Logger lie on the back seat.
This Display is battery-oprated and very portable being only 6x2.5x1.3 in.
The Logger transmits a message every 10 sec providing altitude, temperature, humidity and car battery voltage. It also measures the voltage of its own two re-chargable batteries.
There are two buttons on the top which select what to display.

Here are photographs

Here are the circuit diagrams

Here is the code