The Personal Light Electric Vehicles (a.k.a. Personal Transporters) are getting more and more popular in our cities to avoid using our big polluting cars. I personally use an electric unicycle and I love it, but originally it comes with a very simple charger which doesn't give any charge info, and can't be smart controlled (for instance to stop charging at 80%).

For this reason I decided to make some power meter with capabilities to control and monitor the charge in any moment. There are already some similar devices, and I got inspired by the Charge Doctor. But I wanted something more specific, and it needed to be suited to my needings. That's how ChargeMetge was created.

What does Metge mean? Well I come from a city in Spain called Valencia, and the word to say "Doctor" in valenciano (one of the official languages) is "Metge", that's how the name appeared.

So what can this device do? Good question. I provide the following features:

1) Powered on from the same original charger (no batteries, no USB cables, as simple as possible), and with reverse protection to avoid burning your board.

2) Can monitor voltage, current and temperature using some OPAMP's configured to do so.

3) Can control the voltage output by using a N-channel MOSFET, so you can stop charging whenever you want (according to a voltage related to the battery energy).

4) Can inform you about specific events (charge finished, overvoltage, overcurrent...) by using two LED's and a buzzer.

5) Can be controlled by using three push buttons, completely configurable.

6) Can be programmed very easily by using the Arduino IDE and USB.

7) It's very cheap to build, it was one of the main focuses of this project.

As you can see, I use an Arduino Nano and a LCD 1602 display which are very cheap to buy. The board is 2-layer 100mmx60mm with the smallest design rules allowed by PCBWay to make it for a cheap price.

I used a very simple Arduino code to monitor voltage, current and power:

// CHARGE METGE 1.0 BY CARLOS ARCOS (info@carlosarcos.es)
// WRITTEN CODE FOR THE OPEN-SOURCE CHARGE METGE
// VERSION 0.1

#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);          // LCD PIN DEFINITION
int Vinput = A0;
long Iinput = A1;
int Temp = A3;
int Charge_ON = 2;

void setup() {                                // PROGRAM SETUP
  lcd.begin(16, 2);                           // INITIALIZE LCD
  lcd.clear();
  pinMode(Vinput, INPUT);
  pinMode(Iinput, INPUT);
  pinMode(Charge_ON, OUTPUT);
  lcd.setCursor(0,0);
  lcd.print("CHARGE METGE 1.0");
  delay(1000);
  digitalWrite(Charge_ON, HIGH);
  lcd.setCursor(0,1);
  lcd.print("CONNECTED");
  delay(1000);
}

void loop() {
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print(analogRead(Vinput)/9.553); // Prints value on Vinput to LCD, callibrated
  lcd.print("V");
  lcd.setCursor(9,0); // Text offset to separate
  lcd.print(analogRead(Iinput)*1000/231); // Prints value on Iinput to LCD, callibrated
  lcd.print("A");
  lcd.setCursor(0,1);
  lcd.print("Pout=");
  lcd.print((analogRead(Vinput)/9.553)*(analogRead(Iinput)*1000/231)); // Prints value on V*I to LCD
  lcd.print("W");
  delay(1000); // Refresh every second
}

And with this code you will see something like this:

Of course the idea is to add new features by using the different peripherals, but it's a nice way to test it.

I made a simple test to see how it behaviors thermally using an IR camera, and I didn't see any problems.

I still didn't make any enclosure, but I generated the .STEP file with the complete board already assembled, so it can be 3D printed and modified as desired!

Of course it can be improved. I already noted some things to be replaced in a next version, but hey, this one works! I provide all the files needed to build it, so if you want to try it, just do it!