user48527: My Arduino Mini board has DHT22 temperature sensor and 433MHz radio transmitter modules. I'm using DHT and RCswitch libraries to make use of them. Code looks like this:
void setup() {
  tempSwitch.enableTransmit(RADIO_PIN);
  dht.begin();
}

void loop() {
  float temp = dht.readTemperature();

  unsigned long message = createTemperatureMessage(SENSOR_ID, temp);
  tempSwitch.send(message, 32);

#ifdef MY_DEBUG
  unsigned int sleepCount = 1; 
#else
  // 3600s / 2 / 8s == 225
  unsigned int sleepCount = 225;
#endif
  for (; sleepCount > 0; sleepCount--) {
    LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
  }
}

So I'm reading temperature and sending it using RCswitch library. Initially I just had delay(1000); instead of fancy LowPower sleep loop but I wanted to make my "device" more battery-friendly so I switched to low-power sleep.
The problem is that now Arduino is only sending data first time and after sleeping 30 minutes (in "release" mode) it does not send anything anymore. If I reduce 30 minutes to 8 seconds it is capable of sending data as well as if I replace sleep with delay(30*60*1000);.
From beyond it looks like something is not caching up after the sleep. Do I need to "wake" radio module in any special way? How to fix that?

user10394: I've never tried this, but if you are putting the Arduino to sleep I would expect it to cut power to the devices (does it?) if it does then after a 30 minute sleep I would expect the devices to come back up in the initial state.  Guessing by your code the initial state of the radio is Tx Disabled, so try moving the
tempSwitch.enableTransmit(RADIO_PIN);

to before the 
float temp = dht.readTemperature();

line.
I'd also be concerned that the DHT22 is not in the correct state after you wake up.
Can you try doing a 1 second LowPower sleep in debug mode, I suspect it would work more often.

48527: <p>My Arduino Mini board has DHT22 temperature sensor and 433MHz radio transmitter modules. I'm using <code>DHT</code> and <code>RCswitch</code> libraries to make use of them. Code looks like this:</p>

<pre><code>void setup() {
  tempSwitch.enableTransmit(RADIO_PIN);
  dht.begin();
}

void loop() {
  float temp = dht.readTemperature();

  unsigned long message = createTemperatureMessage(SENSOR_ID, temp);
  tempSwitch.send(message, 32);

#ifdef MY_DEBUG
  unsigned int sleepCount = 1; 
#else
  // 3600s / 2 / 8s == 225
  unsigned int sleepCount = 225;
#endif
  for (; sleepCount &gt; 0; sleepCount--) {
    LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
  }
}
</code></pre>

<p>So I'm reading temperature and sending it using <code>RCswitch</code> library. Initially I just had <code>delay(1000);</code> instead of fancy <code>LowPower</code> sleep loop but I wanted to make my "device" more battery-friendly so I switched to low-power sleep.</p>

<p>The problem is that now Arduino is only sending data first time and after sleeping 30 minutes (in "release" mode) it does not send anything anymore. If I reduce 30 minutes to 8 seconds it is capable of sending data as well as if I replace sleep with <code>delay(30*60*1000);</code>.</p>

<p>From beyond it looks like something is not caching up after the sleep. Do I need to "wake" radio module in any special way? How to fix that?</p>
 10394: <p>I've never tried this, but if you are putting the Arduino to sleep I would expect it to cut power to the devices (does it?) if it does then after a 30 minute sleep I would expect the devices to come back up in the initial state.  Guessing by your code the initial state of the radio is Tx Disabled, so try moving the</p>

<pre><code>tempSwitch.enableTransmit(RADIO_PIN);
</code></pre>

<p>to before the </p>

<pre><code>float temp = dht.readTemperature();
</code></pre>

<p>line.</p>

<p>I'd also be concerned that the DHT22 is not in the correct state after you wake up.</p>

<p>Can you try doing a 1 second LowPower sleep in debug mode, I suspect it would work more often.</p>
