LTC4067 battery charger with Automatic Battery Charging/Load Switchover

It provides power for the circuit and charges the backup single-cell lithium battery while greatly extends battery life. It lets you monitor voltages and currents. It has suspend mode, which reduces current consumption to around 40μA. The power source is a small, 5V solar cell. Connections:

• analog input A1 on ATmega 328 is /CHRG signal from LTC4067

• analog input A0 on ATmega328 is battery voltage

• analog input A2 is solar cell voltage

• analog input A6 is input current ( I=V/R x 1000 )

• analog input A7 is battery charge current ( I=V/Rprog x 1000 )

• digital output A9 - drive it high to put LTC4067 in SUSPEND mode

There is a sample code to read all this info in the source code link

Please refer to technical data sheet of LTC4067 for more information. It is available here:

Official web page for LTC4067

Or, send me a message.

And this is the link to the schematic

The two trimmer potentiometers are used to determine the current for both the input side - to better match the internal resistance of the solar cell - and for the battery charge current. At shipping they are both set to around 2.5kOhm, which set both currents to about 75mA.

Voltmeters on both battery and solar cell connections

They are connected to analog inputs A0 and A2 on the ATmega328p. The voltage dividers resistors are equal, so the measured voltage is double the shown voltage.

Other features on the board:

• NRF24l01+ radio socket

  with CE and CSN pins connected to digital pins 7 and 8 ( you use RF24 radio(7, 8); in Arduino code). There is a 4.7uF capacitor connected across Vin and GND of the port

• low consumption LDO voltage regulator

  The board comes with a Torex XC6210 3.3V voltage regulator . It has low power consumption of 35μA, while delivering at least 700mA. Voltage drop is 50mV @ 100mA.

• two breakout ports with SDA, SCL lines

  and 10k pull-up resistors for external I2C components, connected to A4 and A5

• ESP8266 ESP-01 socket

  breakout pins are for power supply, GND, RX, TX, RST, CH_PD, GPIO0 and GPIO2. RX, TX and CH_PD pins are connected via solder jumpers, not to interfere with programming.

• 3amp 30V n-channel MOSFET

  for regulating external components such as solenoids. The gate is connected to D3 and the output is protected with a Schottky diode.

• low power (2mA) LED diodes

  that are connected via solder jumpers. Jumpers need to be soldered in.

There are few such boards available and none with this kind of versatility. Fully Arduino compatible with Arduino PRO Mini 3.3V @ 8MHz bootlader.

This board is made for solar powered applications with li-po single cell batteries as backup. Identical - small - footprint as Arduino PRO. Only better. It is intended for sensor applications and can be used as an universal board for sensor node networks. Dimensions are 2 inch x 2.1 inch. The board is 1mm narrower than Arduino PRO, to fit into 2inch slot of an enclosure.

For higher voltage applications take a look at Astri arista.