SparkFun ProMicro 3.3v and Xbee Radios

I’m just starting to experiment with XBee radios, and I’m following a tutorial for creating a simple doorbell circuit (taken from the Wireless Sensor Networks O’Reilly book), but while I’ve followed all the directions to a tee. The “button” circuit doesn’t seem to be transmitting anything. Here’s the “button” code:

int BUTTON = 2;

void setup() {
  pinMode(BUTTON,INPUT);
  Serial.begin(9600);
}

void loop() {
  if (digitalRead(BUTTON) == HIGH)  {
    Serial.print('D');
    delay(10);
  }
}

And here’s the “bell” code (I didn’t actually have a bell, so I’m just using an LED on pin 5 to detect any signal):

int LED = 5;

void setup() {
  pinMode(LED,OUTPUT);
  Serial.begin(9600);
}

void loop() {
  if (Serial.available() > 0) {
    if (Serial.read() == 'D') {
      digitalWrite(LED,HIGH);
      delay(10);
      digitalWrite(LED,LOW);
    }
  }
}

I’ve attached the schematics for both the BUTTON circuit and the LED circuit. I’ve verified that both XBee’s are on the same PAN ID, and that each one has the other’s HIGH and LOW addresses as their destination HIGH and LOW attributes. And I can verify in the Serial Monitor when watching the BUTTON circuit that a ‘D’ is being serially printed. But the BUTTON ProMicro’s transmit LED isn’t flashing. Could this because I’m using USB to power them? Does this somehow interfere with transmitting serially?

Well, it doesn't seem to be the USB cord I'm using to power the board that's interfering with the transmission. I attached a battery power supply, and the transmit LED still didn't light up when I was holding the button.

How much current does the radio use when transmitting? I'm working with some raw RFM-22B radios, and at their higher power settings, they can't get enough current from the USB. Try using a big capacitor on the power supply to help keep the voltage steady while transmitting.

Sorry for the delay. The peak current during transmission is 45mA@3.3v. I don't think that would be an issue.

Sorry, to be more specific, the XBee radio's peak transmission current draw is 45mA@3.3v, and the Pro Micro 3.3v's maximum current output on it's VCC pin is 500 mA@3.3v.

What XBees are you using?