NRF24L01 Connection Not Working

Question

I have an ATTiny85 connected to an NRF24L01+ module using this wiring diagram: diagram. The ATTiny85 periodically goes in and out of sleep to send some value to a receiver, an Arduino Uno. If the ATTiny is running off the Arduino power supply (3.3v), everything works correctly. When I run the ATTiny off of a separate CR2032 coin cell that delivers around 3v, the Arduino never receives any data. I have a status LED hooked up to the ATTiny to ensure that the ATTiny is waking correctly, which it is. Here's the code for both:

EDIT: Connecting it to an external 3.3v not from the Uno makes everything work - why wouldn't the coin cell's voltage work? I think everything is rated below 2.8v, the CR2032 minimum.

ATTiny Code

#include <avr/sleep.h>
#include <avr/interrupt.h>

// Routines to set and claer bits (used in the sleep code)
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

#define CE_PIN 3
#define CSN_PIN 3 //Since we are using 3 pin configuration we will use same pin for both CE and CSN

#include "RF24.h"

RF24 radio(CE_PIN, CSN_PIN);

byte address[11] = "SimpleNode";
unsigned long payload = 0;

void setup() {
  radio.begin(); // Start up the radio
  radio.setAutoAck(1); // Ensure autoACK is enabled
  radio.setRetries(15,15); // Max delay between retries & number of retries
  radio.openWritingPipe(address); // Write to device address 'SimpleNode'
  pinMode(4, OUTPUT);
  digitalWrite(4, HIGH);
  delay(500);
  digitalWrite(4, LOW);
  delay(500);
  digitalWrite(4, HIGH);
  delay(500);
  digitalWrite(4, LOW);
  delay(500);
  digitalWrite(4, HIGH);
  delay(500);
  digitalWrite(4, LOW);
  delay(1000);
  setup_watchdog(6);
}

volatile int watchdog_counter = 0;

ISR(WDT_vect) {
  watchdog_counter++;
}

void loop() 
{
  sleep_mode(); //Go to sleep!

  if(watchdog_counter >= 5)
  {
    digitalWrite(4, HIGH);
    watchdog_counter = 0;
    payload = 123456;
    radio.write( &payload, sizeof(unsigned long) ); //Send data to 'Receiver' ever second
    delay(1000);
    digitalWrite(4, LOW);
  }
}



//Sleep ATTiny85

void system_sleep() {

  cbi(ADCSRA,ADEN);                    // switch Analog to Digitalconverter OFF

  set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
  sleep_enable();

  sleep_mode();                        // System actually sleeps here

  sleep_disable();                     // System continues execution here when watchdog timed out 

  sbi(ADCSRA,ADEN);                    // switch Analog to Digitalconverter ON

}

// 0=16ms, 1=32ms,2=64ms,3=128ms,4=250ms,5=500ms
// 6=1 sec,7=2 sec, 8=4 sec, 9= 8sec
void setup_watchdog(int ii) {

  byte bb;
  int ww;
  if (ii > 9 ) ii=9;
  bb=ii & 7;
  if (ii > 7) bb|= (1<<5);
  bb|= (1<<WDCE);
  ww=bb;

  MCUSR &= ~(1<<WDRF);
  // start timed sequence
  WDTCR |= (1<<WDCE) | (1<<WDE);
  // set new watchdog timeout value
  WDTCR = bb;
  WDTCR |= _BV(WDIE);
}

Receiver Code

#define CE_PIN 7
#define CSN_PIN 8

#include <SPI.h>
#include "RF24.h"

RF24 radio(CE_PIN, CSN_PIN);

byte address[11] = "SimpleNode";
unsigned long payload = 0;

void setup() {
  while (!Serial);
  Serial.begin(115200);
  radio.begin(); // Start up the radio
  radio.setAutoAck(1); // Ensure autoACK is enabled
  radio.setRetries(15,15); // Max delay between retries & number of retries
  radio.openReadingPipe(1, address); // Write to device address 'SimpleNode'
  radio.startListening();
  Serial.println("Did Setup");

}

void loop(void){
  if (radio.available()) {

    radio.read( &payload, sizeof(unsigned long) );
    if(payload != 0){
        Serial.print("Got Payload ");
        Serial.println(payload);
    }
  }
}

Is the problem here that the ATTiny and Uno need to be turned on at the same time to establish a connection, or is it something to do with the battery, or something else entirely? Any help would be appreciated.

Answer 1

I was just researching the exact question and I have some bad news.

The ORIGINAL nrf24l01+ alone use around 10-12 ma in transmitting, but unoriginal might even draw more. (https://www.sparkfun.com/datasheets/Components/SMD/nRF24L01Pluss_Preliminary_Product_Specification_v1_0.pdf)

Nevertheless a standard CR2032 battery is simply not made to supply more than a few milliamps at the best, leaving your nrf24L01+ lacking enough current.

There is something called shockburst which can lower your consumption considerably at the cost of range - but if it will succeed in transmitting with one CR2032 I'm not sure about.

Edit: If you add a capacitor you need to cover at least a 10ma drain for around 15ms (turn on - send - turn of immediately), that will require a minimum of a 200µF capacitor at 3V to be able to deliver the current while keeping above 2.0v.