Hi everyone,
I'm doing something stupid. Hopefully someone can tell me what.
I have a TTN UNO (it's based on the Leonardo). Serial0 is the traditional USB/power connection and Serial1 is used for comms to the LoraWAN modem internally. In my project I'm trying to have the TTN Uno power up every hour (triggered by an RTC and powered by a battery via a little circuit), take a measurement, send measurement to TTN and power off again. It's works some times but will at some point fail. Without a serial console it is difficult to know at what point it is failing. As I don't have spare serial point (can't power from normal USB in my project as it would always be on) I'm using the SoftwareSerial library and digital pins 10 and 11 to create a serial connection for debugging. The SoftwareSerial port works. However, when I power up the TTN Uno (switched USB lead from battery) the TTN Uno won't start unless I hit the reset button. I have a small test sketch that flashes an LED in loop(). If the CP2101 TTLtoUSB serial port is plugged into my computer and connected to the TTN Uno (pins10/11/GND) the TTN Uno will not start until the reset buttong is pressed. If the TTLtoSerial converter is connected to the TTN UNo but not the PC, it starts fine. I see ~2.6v on pin 10 (connected to TXD of USBtoTTL converter) and 0v on pin 11 (RXD) when the converter is plugged in to the PC but the TTN Uno is unpowered.
The current sketch on the board doesn't use these pins or SoftSerial (I've stripped it back). Here it is below. Question is, why won't the TTN UNo start if pins 10/11 are connected to a TTLtoUSB converter plugged into an active PC?
#define LED 6
void setup()
{
pinMode(LED, OUTPUT);
delay(2000);
}
void loop()
{
while (true)
{
digitalWrite(LED, HIGH); //until code decides to turn it off
delay(1000);
digitalWrite(LED, LOW); //until code decides to turn it off
delay(4000);
}
}