Sunday, July 23, 2017

18650 Li-Ion battery powered Wemos D1 with Wemos Battery Shield - DONE 30 days achieved

Wemos has developed a series of shields for the Wemos D1 :

  • DHT Shield
  • Battery Shield
  • Matrix LED Shield
  • Buzzer Shield
  • Dual Base
  • SHT30 Shield
  • WS2812B RGB Shield
  • ProtoBoard Shield
  • 1-Button Shield
  • Micro SD Card Shield
  • Relay Shield
  • DC Power Shield
  • Tripler Base
  • Motor Shield
  • OLED Shield

The good thing is that you can stack them on top of another.

Let's take a look for now to the Battery Shield that is now on version 1.2.0 and it has a retired version 1.1.0

Get the schematics from here version 1.1.0 and 1.2.0 to see the differences. An immediate visual difference is the inductor on the V1.1.0 is much higher than the one on V1.2.0 but is not all.

Battery Shield V1.1.0

Since I didn't found yet the version 1.2.0, I used the V1.1.0 from here. and the Wemos D1 mini from here. I've also added an BMP180 pressure and temperature sensor.


  • Charging Voltage: max: 10V, recommend: 5V
  • Charging Current: max: 1A
  • Lithium Battery voltage: 3.3-4.2V
  • Boost Power Supply: 5V(max: 1A)

 Connections between the Wemos D1 mini and Battery shield:

D1 mini Shield
5V         5V(max: 1A) Power Supply
A0           Vbat f the jumper J2 is closed.

Now for the battery. Since I didn't find a decent LiIon flat battery on a good price I had to improvise and I've dismounted a EUR 5 Innergie 2600mA power bank.

Original Power Bank

I have disassembled the power bank and I've get the battery from it.

Samsung 18650 Li-Ion battery. Nice !!!

Then I've added the battery to this EUR 1 battery holder from

Battery is charging 

I've connected the Battery Shield's miniUSB to 5V to charge the battery and the red LED start to light. When the battery was charged the LED red turned off and LED green turned ON signaling that the charging is done.  After I've removed the USB cable from the Battery Shield the green LED turned off not to consume from battery. At this moment I've added the BMP180 and flash the firmware.


This is happening when the battery is shorted. Don't try it at home. This was done so you not have to try it.

Melted wires and battery holder.

To log the battery level I've used again the good service offered by the and log
the A0 value, a computed voltage which is not accurate at this time since I didn't had a voltmeter with me to do it.

#include <ESP8266WiFi.h>
#include <Wire.h>
#include <Adafruit_BMP085.h>

Adafruit_BMP085 bmp;

unsigned int raw=0;
float volt=0.0;

void setup() {
  if (!bmp.begin()) {
    Serial.println(F("Could not find a valid BMP180 sensor, check wiring!"));
  const char* ssid     = "WIFI_SSID";
  const char* password = "WIFI_PASSWORD";
  const char* host = "";

  pinMode(A0, INPUT);
  raw = analogRead(A0);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
  Serial.println(F("Connected to WiFi"));
  String v=String(volt);// change float into string
  // make TCP connections
  WiFiClient client;
  if (client.connect(host,80))  // "" or
      String postStr = apiKey;
      postStr +="&field1=";
      postStr += String(v);
      postStr +="&field2=";
      postStr += String(raw);
      postStr +="&field3=";
      postStr += String(bmp.readPressure()/100);
      postStr +="&field4=";
      postStr += String(bmp.readTemperature());
      postStr +="&field5=";
      postStr += String(bmp.readAltitude());      
      postStr += "\r\n\r\n";
      client.print("POST /update HTTP/1.1\n");
      client.print("Connection: close\n");
      client.print("X-THINGSPEAKAPIKEY: "+apiKey+"\n");
      client.print("Content-Type: application/x-www-form-urlencoded\n");
      client.print("Content-Length: ");
  ESP.deepSleep( 10 * 60 * 1000000 ); //10 minutes  

void loop() {


For connecting the BMP180 to Wemos D1 mini see this post. 

The Wemos will enter in sleep mode and every 10 minutes will wake and log the data to cloud.

Don't forget to connect the RST pin to D0 to activate the deep sleep.

The 5V to 3V3 on the Wemos is always  powers so there is some energy lost on it but is ok.

After one day the graph is looking like this:

Total cost: EUR 14.

[ EDIT 1 ] 5 days later after 700 measurements the graph is:

I am considering adding a solar panel to charge the battery during the day.

5 days later
[ EDIT 2 ] I've measured battery's voltage today and the deviation is 0.5V. So I need to add 0.5V over the calculated value. Voltage measured on battery after 5 days is 4.11 V.

I don't find the any information if the shield module will stop providing voltage to Wemos D1 if the battery voltage drop under the 3.6 V or will dry the 18650 battery, but my guess is that will stop at 3.6 V.

[ EDIT 3 ] After 9 days the battery has 4.06 V

9 days later

[ EDIT 4 ] After 11 days the battery has 4.03 V
11 days 

[ EDIT 5 ] After 13 days the battery has 4.00 V. For one day the router decided to take a break. It looks like the battery still have 0.4 V left and it is enough for the rest of the month. I predict that the module can run 30 days without problems with only one charge. Discharging rate is is pretty linear and I hope it will stay linear.

13 days later
[ EDIT 6 ] After 16 days - 3.943 V

[ EDIT 7 ] After 30 days - 3.8 V

The second interruption was deliberate ( I had to travel ).


After 4160 records logged with a single charge of one 18650 battery there is still some power left
for at least one week. In conclusion you can use the WeMos D1 ,  Wemos Battery Shield and one 18650 to get and log data at 10 minutes interval with a single charge for more then one month.

[ EDIT 8 ] After  2 hours charge the module is ready for another month of working. I've added a trigger to be notified via twitter when the voltage is bellow 3.7 V to charge it again.

Ready for a new month

[EDIT 9] I have now  38 days with one charge. Remember, every 10 minutes is measuring the temperature and post it on then is entering again is deep sleep

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