     }
     else if (millis() - lastHeartbeat >= HEARTBEAT_THRESH_MILLIS) {
         // Re-use ack byte for heartbeat
-        validateAck(sendByte(triggerVal));
+        validateAck(sendByte(ackVal));
     }
 
     digitalWrite(heartbeatLEDPin, isCommHealthy);

        }
        else {
            radio.read(&recvByte, 1);
            Serial.print("Received ack byte " + recvByte);
        }
    }
    else {

}

void validateAck(byte ackResponse) {
    if (ackResponse == ackVal) {
        isCommHealthy = true;
        Serial.println("Comms healthy");
    }
    else {
        isCommHealthy = false;
        Serial.println("Bad ack received! This probably means that the connection is unstable.");
