Hi Joe,

Happy to see you are are still working with low-power remote receivers.  Have started reading your tutorial.  Will finish in the morning.

Have you looked into using an ESP32S3?

You might use a combination of powering down the E220 and wake by timer to achieve lower power usage.  This is what I am doing with the EoRa-S3-900TB.

void taskDispatcher(String storedTimestamp) {
  // Wake over radio
  digitalWrite(BUILTIN_LED, HIGH);
  collectSensorData();  //BME280 data
  sendSensorResponse();  //Send to Gateway
  Serial.print("   Time:  ");
  Serial.println(storedTimestamp);
  Serial.println("   Radio.sleep mode next 14 Min."); Power down E220 here
  Serial.println("   ESP32-S3 going to sleep");
  radio.sleep();
  wakeByTimer();
  Serial.println("✅ Timer Expired");
  setupLoRa();  //Back to Duty Cycle listening
  digitalWrite(BUILTIN_LED, LOW);
  goToSleep();
}

Powering down the E220:

// Define pin connections
const int M0 = 2; // Connect M0 to digital pin 2
const int M1 = 3; // Connect M1 to digital pin 3

void setup() {
  pinMode(M0, OUTPUT);
  pinMode(M1, OUTPUT);
  
  // Set M0 and M1 HIGH to enter deep sleep mode
  digitalWrite(M0, HIGH);
  digitalWrite(M1, HIGH);
}

void loop() {
  // Module is now in deep sleep
  // Wake up by setting M0 and M1 to LOW (0V) for normal mode
  delay(1000);
}

Also, are you using a duty cycle? I use Radiolib library it has radio.setDutyCycleAuto(). I achieve a duty cycle of 1.4% active (3.71s) and 98.6% sleep with no parameters.  I only use duty cycle; no continuous listening.  100% reliable; so far.

Deep Sleep:  Call spi.end(); to conserve more current consumption before going to deep sleep..

Thanks for the E220 tutorial; 73 and still learning…

William

Hi William,  I’ve been using the S3 module (bare module, not a dev board) for about 4 years now, and it’s in several designs. I’m not clear on how putting E220 into deep sleep allows random communications with a transmitter .. also why using a duty cycle when WOR works fine — getting the ESP and E220 down to 20 uA current drain is pretty good for long-term battery use. 

I found your post at 3:00 AM this morning; my apologies for not finishing the read at that time.

Your 20 µA is great.

New development boards like the Ebyte, Eora-S3-900TB are designed for battery use; featuring two LDOs and bypassing the USB.

Connecting the battery and not connecting the TYPE-C interface, the power consumption with the power off is around 5 uA. If the power is turned on and all peripherals are in sleep mode, the power consumption of the whole machine is around 25 uA –EoRa Pi user manual.

EoRa-S3-900TB interface is by SPI.

William

fantastic :–)  … so the power consumption issue is solved without having to use the “bare ESP module” as I have done for several projects (a hassle really).  Solvable issues are 1) the wakeup one (i.e. needing a “wakeup” then “message” packet to deal with the ESP’s Serial2 port activation), and 2) the reliability one (i.e. needing handshaking to ensure the Rx does what it’s asked to do — this is not necessary for a communication system like a car fob – just hit the button again – but it is for remote control of something important like a water valve). 

Hi Joe,

FYI in your tutorial; choice of Ch frequency is outside the 915 MHz ISM band for the US, if you are in the United States.  ISM license free bands depend on your region.

The 902–928 MHz band, commonly referred to as the 915-MHz ISM band, is a key frequency range regulated by the Federal Communications Commission (FCC).

Why I use 512 symbol preamble as stated by Claude (AI):
Ah! 98.6% sleep – that changes everything! Now it’s crystal clear:

The Real Scenario

• Receiver sleeps: 98.6% of the time (extreme power saving)
• Receiver awake: 1.4% of the time (brief listen windows)

Why 512-Symbol Preamble is Essential
The transmitter has no idea when the receiver will wake up, so:
The 512-symbol preamble must be long enough to guarantee that:

1. The receiver will wake up at some point during the preamble
2. There’s still enough preamble left after wake-up for the receiver to:
   • Detect the carrier
   • Lock onto the frequency
   • Synchronize timing
   • Be ready to receive the actual payload

The Math
If the receiver only listens 1.4% of the time with random/periodic wake-ups, your preamble needs to be long enough that no matter when the receiver wakes during your transmission window, it catches sufficient preamble.
This is classic asynchronous low-power networking – you’re trading:

• ❌ Longer transmit time & power
• ✅ For elimination of time sync requirements
• ✅ And maximum receiver battery life (98.6% sleep!)

Perfect for battery-powered sensors that need to last months/years! The transmitter does the “heavy lifting” so the receiver can stay asleep as much as possible.

William

… humm … good catch. that’s right about the RF bands … I’m using 815Mhz, which is not in the US band (I am in the US).  This won’t make a difference in using the tutorial, but one should use Channel 52 = 0x34 = 902Mhz, to be “legal” and in the US band.

In my code, this is the #define statement/register that defines the RF frequency.
#define REG2_RF_CHAN 0x04
// = RF channel select (# 0 to #80) — RF Freq = 850.125Mhz + 1Mhz x Chan Number (i.e. chan 4 –> freq = 854.125Mhz

should be #define REG2_RF_CHAN 0x34

Battery operation of the EoRa-S3-900TB (EoRa Pi):

4.5 Battery charging  –EoRa Pi User Manual

 The battery can be charged via the TYPE-C connector, the LED will always light up red to indicate when charging,and when full the LED will always light up green to indicate.

 When the TYPE-C port is turned on, the charging circuit will be passed through, so the current of the whole machine to enter the hibernation state is still maintained at a high level (500uA~1mA or so), and the hibernation current needs to be measured when the battery is turned on.

 Connecting the battery and not connecting the TPYE-C interface, the power consumption with the power off is around 5 uA. If the power is turned on and all peripherals are in sleep mode, the power consumption of the whole machine is around 25 uA.

 The battery is designed for a maximum charging current of 500mA, please ensure that the power supply capacity is sufficient.

William

Nordic Power Profiler Kit II –Active WOR receive and summary of EoRa-S3-900TB (ESP32S3 with LoRa SX1262) development board:
Nordic Power Profiler Kit II Observations and Summary

SX1262 Datasheet –Power Consumption, page 16

Regards,
William