16F88 Volt-ampermeter - LCD 2x8

Intro
As I experiment a lot in RC electronics, I really needed a way to easily monitor the voltage and the current drawn by motors while testing the power circuits.

I wanted to make my own volt-ampermeter to have it handy. The Internet is full of them, so there is really nothing new or innovative in my instrument, but here is my version.

It displays the voltage and the amps in the below format:

1st line:  U = 12.34V 
2nd line: I  = 1.234A 

Comps
I chose to use a 16F88 I had, a small 8x2 LCD (unfortunatelly no backlit, a cheap $3-4) and a small 2.5" by 3.5" by 1" ABS box (the type with a 9V battery compartment). The box height does not allowed the LCD to be installed inside, so I still have to figure out some screen protection shield. See figure 1 below:

Figure 1 - Click to zoom in

I chose a rail-to-rail opamp as a buffer and signal amplifier. You can see the schematic below. No explanations needed. It is really minimalistic version, while all calibration is software (by means of calculate, implement and test - wasn't easy, but I tried to minimize the component count); I wish I would have put there 2 pots for the ease of calibration - I'd suggest you do it if you have a bigger box in your plan to build this instrument. See figure 2 below.

Figure 2 - Click to zoom in

Note that the PCB I made allows for the PIC PCB (right side of the schematic) to be stacked on the V-A interface (left side of the schematics). The pot for the LCD contrast is soldered directly on the LCD so it is not shown in the schematic, while R/W, D0 to D3 are all grounded directly on the LCD.

Firmware
The Mikrobasic PRO source and HEX are here!

Notes:
Remember that 1A leads to 0.1V voltage drop only in the 0R1 shunt; 5A lead to 0.5V drop. I have not considered the drop on the power wires (and the drop is maybe more than in the shunt itself). Use short wires and make sure they're properly sized (AWG10 or 4sqmm I would recommend).