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This Instructables show how to use an Arduino Nano to charge some small LTO battery in constant current constant voltage basic.

Step 1: Why LTO Battery?

Lipo battery is around 4.2 V when fully charged, it is a little bit too high to power a 3.3 V board (like ESP8266) without regulator. You may found a little bit too hot on the metal case surface.

LTO battery has lower voltage relatively. It is around 2.9 V when fully charged.

LTO battery also claim it can charge in larger current (charge faster) and more safety.

Step 2: Preparation

Bread board

I use 2 small bread boards connect vertically, it can make the circuit more neatly

Arduino board

I use an Arduino Nano, other Arduino model should also work

Display

I use a SSD1331 breakout board, any Ucglib supported display should be ok

Current monitor

INA219 breakout board

PNP transistor

I use A1013, any PNP transistor that can support the charge current (my LTO battery is 60 mA if charging in 1 C) should be ok

Battery connector

I use 2 Alligator Clips with Pigtail

LTO battery

I bought a 60 mAh LTO battery

Step 3: Bread Board Circuit

Here are the connection summary:

INA219 breakout board

Vcc  -> Arduino 3.3 V pin
Gnd  -> Arduino Gnd pin, Battery -ve
Scl  -> Arduino A5 pin
Sda  -> Arduino A4 pin
Vin- -> Battery +ve
Vin+ -> PNP transistor Emitter pin

PNP Transistor

Emitter   -> INA219 Vin+ pin
Collector -> Arduino 5 V pin
Base      -> Arduino D10 pin

SSD 1331 OLED display

CS  -> Arduino D2 pin
GND -> Arduino Gnd pin
RST -> Arduino D3 pin
VDD -> Arduino 3.3 V pin
CLK -> Arduino D13 pin
DIO -> Arduino D11 pin
DC  -> Arduino D7 pin

Step 4: Program

Here is the Arduino program summary:

  • check charge current and voltage from INA219
  • control the output PWM to meet constant current constant voltage charging method
  • calculate the charged power
  • display figure and plot the graph

Step 5: Happy DIY!

You may now make your next projects much smaller by saving the voltage regulator space.

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