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.

• Avamander: Yes, receiver needs to be listening while another one is transmitting to receive packets.
• Avamander: Also, try setting the PA level lower.
• Gerben: Coin cells can't deliver a lot of current. To account for the short bursts of higher current (during transmission) you can put a capacitor in parallel to the battery.
• Alex Wulff: Good call, I'll try it with a capacitor. Would 10uF be not enough, or too much?
• Avamander: Experiment. Also set the PA level lower so that the radio would consume less power. tmrh20.github.io/RF24/… (You are using github.com/TMRh20/RF24, right?)

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.

• Alex Wulff: Hmmm... this is very good to know. I had some 100µF capacitors lying around and, after testing, it appears that it is transmitting, albeit after setting the PA level to its lowest setting. Not sure if it works on a higher PA level. Looks like that capacitor seemed to do the trick.
• Mikael: Glad to hear it, I used values think you should have enough power
• Mikael: I tried to say you likely have enough capacitance for high PA level if it is burst only. Otherwise you could add more capacitors - or switch to a power source with higher current capabilities