NRF24L01 with ATTiny and Uno not connecting - arduino

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'm experiencing the same problem when running Arduino Nano from a battery.
Nano has a 3.3V pin that I'm using for powering the NRF24L01+ module.
When the voltage from my battery-pack drops under 3.3V, the 3.3V pin voltage also drops. After few minutes, the RF module is not sending any messages.
I fixed the problem temporarily by routing the battery through a 12V step-up regulator that I bought earlier for a different project. These 12V then go to the "UN" pin on Nano which accepts 6-20V. This setup works nicely but is definitely not optimal.
Therefore I'm planning to use a 3.3V step-up regulator such as Pololu 3.3V Step-Up Voltage Regulator U1V11F3 which, according to the supplier, can efficiently generate 3.3V from input voltages as low as 0.5V.
I think this might be helpful to your project as well.