[PCB] Pro mini / RFM95W / 18650 solar chargeable

Hello LoRa friends,


I recently designed a PCB (my first one) that has the components that are important to me.

Here are some key facts:

  • Arduino Pro mini 3.3V without LED, without regulator (5uA)
  • RF95W (1.5uA)
  • MCP1700-330 LDO (1.6uA, 250mAh max, 2.3-6V input)
  • NCR18650B (3200mA LiPo 4.2V charge, 3.0V cut)
  • TP4056 charger with protection for LiPo (4.2-7V input)
  • Diode for solar module (TP4056 works very well with 5V / 6V solar cells)
  • Resistors, capacitor for measuring the battery voltage at A0 and 1.1V reference
  • Plug’n Play slot for BME280 (temperature, humidity, air pressure over I2C)
  • SMA antenna connector or wire e.g. helical


Price for everything from aliexpress about 15 €.
PCBs from China: 25 € for 30 pieces.

Theoretical battery life in sleep:
Below 10uA Sleep = <0.01mA

3200mAh / 0.01mA = 320k hours = 13k days, 36 years

But beware, a LiPo has about 5% self-discharge per month. With simpler calculation comes to about 2 years.

A small test showed me the consumption in operation:
The node sent 6 bytes per minute on SF7 in CH0 and ABP with Arduino-lmic
Starts at 4.15V. After 48 hours, the battery still had 4.07V.
It is about 2%.

=> 150,000 times sending data!

In 48 hours it sent just under 3k times.

You quickly realize that the standby consumption is not the problem. The sending, as well as the self-discharge is much more important.

Example application: Temperature measurement every 3 hours:
(without standby and self-discharge)
8 times per day -> 50 years.

You quickly realize that the only enemy is the self-discharge, or even extreme temperatures.
Therefore, it should be sufficient to install a small 5V solar cell, so that the battery always remains full, or you just replace the battery every 1-2 years.
Alternatively, 3xAA(A) pack can be connected, but it has only 30% of that much mAh!

If someone of you would like to have a PCB to test, I like to send in EU for a few euros (shipping, PCB costs and the equivalent of a six-pack beer :smiley: )

I look forward to your impressions!

Have a good time! :wink:

Ps. I can also 3D print a housing, if you want … or just share my files!

And the Console-Output (without Temp/hum Sensor!):


It would be interesting to test it. Sketch to use? Dimensions?

1 Like

Thank you! What do you mean by Sketch? PCB design, 3D printing or Arduino code?

Arduino code :slight_smile:

No Problem, but remember, i write it only for first test and used much from Arduino-lmic example, so very dirty.
And i only use a single channel gateway, so if you use a full GW, you must uncomment the block with “LMIC_setupChannel” and delete my definitions!

Good luck & if you have any questions, contact me!

   Copyright (c) 2015 Thomas Telkamp and Matthijs Kooijman

   Permission is hereby granted, free of charge, to anyone
   obtaining a copy of this document and accompanying files,
   to do whatever they want with them without any restriction,
   including, but not limited to, copying, modification and redistribution.

   This example sends a valid LoRaWAN packet with payload "Hello,
   world!", using frequency and encryption settings matching those of
   the The Things Network.

   This uses ABP (Activation-by-personalisation), where a DevAddr and
   Session keys are preconfigured (unlike OTAA, where a DevEUI and
   application key is configured, while the DevAddr and session keys are
   assigned/generated in the over-the-air-activation procedure).

   Note: LoRaWAN per sub-band duty-cycle limitation is enforced (1% in
   g1, 0.1% in g2), but not the TTN fair usage policy (which is probably
   violated by this sketch when left running for longer)!

   To use this sketch, first register your application and device with
   the things network, to set or generate a DevAddr, NwkSKey and
   AppSKey. Each device should have their own unique values for these

   Do not forget to define the radio type correctly in config.h.


#include <Arduino.h>
#include <U8g2lib.h>
#include <lmic.h>
#include <hal/hal.h>
#include <SPI.h>
#include <Wire.h>

// Enable debug prints to serial monitor
#define MY_DEBUG

int BATTERY_FULL = 4.2;

U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE, /* clock=*/ SCL, /* data=*/ SDA);   // pin remapping with ESP8266 HW I2C

// LoRaWAN NwkSKey, network session key
// This is the default Semtech key, which is used by the early prototype TTN
// network.
// DEVEUI und AppEUI **LSB**
static const PROGMEM u1_t NWKSKEY[16] = { 0xAA ....};

// LoRaWAN AppSKey, application session key
// This is the default Semtech key, which is used by the early prototype TTN
// network.
// **MSB**
static const u1_t PROGMEM APPSKEY[16] = { 0xAA ....};

// LoRaWAN end-device address (DevAddr) Write 0x and than the DevADD as Numbers
static const u4_t DEVADDR = 0x0123456789;

// These callbacks are only used in over-the-air activation, so they are
// left empty here (we cannot leave them out completely unless
// DISABLE_JOIN is set in config.h, otherwise the linker will complain).
void os_getArtEui (u1_t* buf) { }
void os_getDevEui (u1_t* buf) { }
void os_getDevKey (u1_t* buf) { }

static uint8_t mydata[] = "Hello, world!";
static osjob_t sendjob;

// Schedule TX every this many seconds (might become longer due to duty
// cycle limitations).
const unsigned TX_INTERVAL = 60;

// Pin mapping for Marioz PCB
const lmic_pinmap lmic_pins = {
  .nss = 10,
  .rxtx = LMIC_UNUSED_PIN,
  .rst = 9,
  .dio = {4, 5, 7}, //DIO0, DIO1 and DIO2 connected

void onEvent (ev_t ev) {
  Serial.print(": ");
  switch (ev) {
    case EV_JOINING:
    case EV_JOINED:
    case EV_RFU1:
    case EV_JOIN_FAILED:
      Serial.println(F("EV_TXCOMPLETE (includes waiting for RX windows)"));
      if (LMIC.txrxFlags & TXRX_ACK)
        Serial.println(F("Received ack"));
      if (LMIC.dataLen) {
        Serial.println(F("Received "));
        Serial.println(F(" bytes of payload"));
      // Schedule next transmission
      os_setTimedCallback(&sendjob, os_getTime() + sec2osticks(TX_INTERVAL), do_send);
    case EV_LOST_TSYNC:
    case EV_RESET:
      // data received in ping slot
    case EV_LINK_DEAD:
    case EV_LINK_ALIVE:
      Serial.println(F("Unknown event"));

void do_send(osjob_t* j) {
  // Read sensor values and multiply by 100 to effectively keep 2 decimals
  // Signed 16 bits integer, -32767 up to +32767
  int16_t t = 0;
  // Unsigned 16 bits integer, 0 up to 65535
  uint16_t h = 0;
  // Unsigned 16 bits integer, 0 up to 65535
  uint16_t b = readBat() * 100;
  byte buffer[6];
  buffer[0] = t >> 8;
  buffer[1] = t;
  buffer[2] = h >> 8;
  buffer[3] = h;
  buffer[4] = b >> 8;
  buffer[5] = b;
  LMIC_setTxData2(1, buffer, sizeof(buffer), 0);

  Serial.print("Sending - temperature: ");
  Serial.print(", humidity: ");
  Serial.print(", battery: ");

  // Check if there is not a current TX/RX job running
  if (LMIC.opmode & OP_TXRXPEND) {
    Serial.println(F("OP_TXRXPEND, not sending"));
  } else {
    // Prepare upstream data transmission at the next possible time.
    LMIC_setTxData2(1, buffer, sizeof(buffer), 0);
    Serial.println(F("Packet queued"));
  // Next TX is scheduled after TX_COMPLETE event.

void setup() {

  // Fuer A0 Battery:

  // For Pinoccio Scout boards
  digitalWrite(VCC_ENABLE, HIGH);

  // LMIC init
  // Reset the MAC state. Session and pending data transfers will be discarded.

  // Set static session parameters. Instead of dynamically establishing a session
  // by joining the network, precomputed session parameters are be provided.
#ifdef PROGMEM
  // On AVR, these values are stored in flash and only copied to RAM
  // once. Copy them to a temporary buffer here, LMIC_setSession will
  // copy them into a buffer of its own again.
  uint8_t appskey[sizeof(APPSKEY)];
  uint8_t nwkskey[sizeof(NWKSKEY)];
  memcpy_P(appskey, APPSKEY, sizeof(APPSKEY));
  memcpy_P(nwkskey, NWKSKEY, sizeof(NWKSKEY));
  LMIC_setSession (0x1, DEVADDR, nwkskey, appskey);
  // If not running an AVR with PROGMEM, just use the arrays directly

#if defined(CFG_eu868)
  // Set up the channels used by the Things Network, which corresponds
  // to the defaults of most gateways. Without this, only three base
  // channels from the LoRaWAN specification are used, which certainly
  // works, so it is good for debugging, but can overload those
  // frequencies, so be sure to configure the full frequency range of
  // your network here (unless your network autoconfigures them).
  // Setting up channels should happen after LMIC_setSession, as that
  // configures the minimal channel set.
  // NA-US channels 0-71 are configured automatically
  //    LMIC_setupChannel(0, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(1, 868300000, DR_RANGE_MAP(DR_SF12, DR_SF7B), BAND_CENTI);      // g-band
  //    LMIC_setupChannel(2, 868500000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(3, 867100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(4, 867300000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(5, 867500000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(6, 867700000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(7, 867900000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  //    LMIC_setupChannel(8, 868800000, DR_RANGE_MAP(DR_FSK,  DR_FSK),  BAND_MILLI);      // g2-band
  LMIC_setupChannel(0, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(1, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7B),  BAND_CENTI);      // g-band
  LMIC_setupChannel(2, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(3, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(4, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(5, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(6, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(7, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);      // g-band
  LMIC_setupChannel(8, 868100000, DR_RANGE_MAP(DR_FSK, DR_FSK),  BAND_MILLI);      // g2-

  // TTN defines an additional channel at 869.525Mhz using SF9 for class B
  // devices' ping slots. LMIC does not have an easy way to define set this
  // frequency and support for class B is spotty and untested, so this
  // frequency is not configured here.
#elif defined(CFG_us915)
  // NA-US channels 0-71 are configured automatically
  // but only one group of 8 should (a subband) should be active
  // TTN recommends the second sub band, 1 in a zero based count.
  // https://github.com/TheThingsNetwork/gateway-conf/blob/master/US-global_conf.json

  // Disable link check validation

  // TTN uses SF9 for its RX2 window.
  LMIC.dn2Dr = DR_SF9;

  // Set data rate and transmit power for uplink (note: txpow seems to be ignored by the library)
  LMIC_setDrTxpow(DR_SF7, 14);

  // Start job

float readBat() {
  int sensorValue = analogRead(BATTERY_SENSE_PIN);
#ifdef MY_DEBUG
  // 2M, 470K divider across battery and using internal ADC ref of 1.1V
  // Sense point is bypassed with 0.1 uF cap to reduce noise at that point
  // ((2e6+470e3)/470e3)*1.1 = Vmax = 5,78 Volts
  // 5,78/1023 = Volts per bit = 0.00565

#ifdef MY_DEBUG
  float batteryV  = sensorValue * 0.00565;
  Serial.print("Battery Voltage: ");
  Serial.println(" V");
  return batteryV;

void loop() {

what about LiLyGo TTGO v2.0?

I did not know the board, but I know many similar ones …
They often cost only 15 € / $, but have far worse properties.
No battery (alone that costs more than half) by far not so low power consumption in sleep. The radio module is often too long away on pcb from the antenna connection. so much loss?!
In addition comes Bluetooth, WiFi which one can use at most as gateway, not as node. Oled exactly the same.
Too much things around and with battery keep the things 1,2,3 months.

Many compromises and no benefits.

1 Like

do you sell a finished product?

strange; 10uA and no lowpower in the code?
so your measurements based on „no sleep“ or did you share a preversion of your code?

If there is demand, then I would do that, gladly! I am a student and I enjoy it. a few euros would be nice! Gladly also in different versions: PCB only, with resistances and co, with everything, with case, …

10mA are indicated by the fact that all components in sleep use exactly that. First measurements have shown that the Arduino-LMIC library also have low power modes. Class A, B, C as a node also plays a role!
I will continue to test and soon measure with shunt and oscilloscope in Lab.
I am studying Computer Engineering and in the university in my lab we have some measurement tool :wink:

I will announce all further findings here!

Please write me if you are interested in such a product and what you are missing and so on …
Then I can think about whether I should sell it!

Thanks for the positive news so far :slight_smile:


OK, so to protect the Lipo, and keep it safe, you need the project to shut down (turn off) when the battery voltage falls to 3.3v or perhaps 3.0V, how does the board do that ?

looking forward for your pcb on PCBs.io :blush:

Jes, the TP4056 is with build in protection. It has a Cut-Off by 2.4V. I think that’s enough, because in the datasheet of NRC18650B is discharged to 2.5V.
Or is it not enough? Then I would have to install an additional protection …

IMG_1421 I like this concept very much… :grinning::grinning::grinning: A litle bit more flexible for different sensors. I will study yours. Exchange schematics?



very funny! :slight_smile:
Good work!

You put pins down to connect easily? That’s what I thought, but I wanted to be as compact as possible …
So that you can easily connect sensors, the pins of the Arduino are a bit above, so you can expand them with your own small perforated boards, or make more PCBs.

One tip:
Forme antenna cables around. I have not learned enough ektrotechnik for me to explain, but everybody does it. In addition, I make holes with GND around it, so I get a slight shielding.

And another tip:
Desolder the LED and the Voltage Regulator from your Arduino. The LED consumes 0.8mA alone! And the regulator 0.05mA.

To the circuit diagram:
I have to be honest and confess that I do not have one. It’s my first own PCB and I did not know about autorouting, so I did everything by hand. The version 2 is completely redesigned and then with schematic!

Nice day! :slight_smile:

Nice Work. I would be interested in a few pieces, prefered with components and (outdoor) case

Hello @marioz

I am interrestet too at your PCBs.

I need some more input at your great work.

Have you some info at the dimensons of that solution?

An BOM (Bill Off Material)!

I don`t know how we can get the requirements.

Makin an surfey in a marketplace-thread?


1 Like

Is there a chance you could share your PCB design, I think it would work great for a project I am working on as well.

Great idea!

1 Like

Love the longboard shape sitting on the back of the battery! Great work…

I’ve been through the rechargeable batteries paths and the self-discharge, especially when temperature varies, is frustrating. I also tried primary non-rechargeable cells, but they’re very, very expensive and need some complicated energy buffering as they cannot deliver more than a 2-5 mA continually (otherwise you cause damage to the cell).

I’ve been experiencing with low-power for while and at the moment having some success with Whisper Nodes and 2xAA. Alkalines are to be cheap and reliable… saying that, I’m really keen to reduce the size of one of my nodes and I’m trying to work with solar harvesting + super-caps (or tiny Li-Po). Found a TI and an ST solar harvesting ICs, just trying it out to see how small can I go with the solar panel. My idea is to transmit every 1h-6h, will post something if I get things to work.