remote-camera-shutter/attiny_SPI_Server/attiny_SPI_Server.ino

#define BUTTON 4

#include <NRF24.h>
#include <SoftSpi.h>

NRF24 nrf24(10,SS);
uint8_t data[1], prev[1];
uint8_t len[1];

void setup() 
{
  pinMode(BUTTON, OUTPUT);
  digitalWrite(BUTTON, LOW);
  delay(1000);
  if (!nrf24.init())
  digitalWrite(BUTTON, HIGH);
  if (!nrf24.setChannel(20))
  digitalWrite(BUTTON, HIGH);
  if (!nrf24.setThisAddress((uint8_t*)"servl", 5))
  digitalWrite(BUTTON, HIGH);
  if (!nrf24.setPayloadSize(1))
  digitalWrite(BUTTON, HIGH);
  if (!nrf24.setRF(NRF24::NRF24DataRate2Mbps, NRF24::NRF24TransmitPower0dBm))
  digitalWrite(BUTTON, HIGH);
  nrf24.spiWriteRegister(NRF24_REG_06_RF_SETUP, NRF24_CONT_WAVE | NRF24_PLL_LOCK | NRF24_PWR_0dBm);
  if (!nrf24.powerUpRx())
  digitalWrite(BUTTON, HIGH);
  len[0] = 1;
}

// With printing commented and delay removed, this can achieve about 666 round trips per second
void loop()
{
  // Configure for carrier wave:
  if(nrf24.recv(data, len)){
    if(data[0]!=prev[0])
      digitalWrite(BUTTON, HIGH);
    if(data[0]==prev[0])
      digitalWrite(BUTTON, LOW);
    prev[0] = data[0];
  }
}