Arduino Pro Mini external power and serial monitor

Development Tools IDE 1.x
1

Hello,

I'm a first timer on the forum. I have a sketch that outputs an analog value from a LDR. I'd like to view it after installation. My Pro Mini and the relay module are powered by a mobile phone charger and installed on the mains.

I'm aware if I disconnect external power and connect VCC, GND, RX, TX from Pro Mini to the TTL-USB adapter, I can read the values on serial monitor of IDE. But I wish to use this serial monitor occasionally.

I have tried connecting the RX and TX alone from the Pro Mini to the TTL to USB adapter trying to view the info in the Serial Monitor. It didn't work. I do not think it is a good idea to connect VCC and GND from the Pro Mini into the adapter with external power connected, because the supply is around 6V.

Is there a way to accomplish this? Or is there a simpler alternative?

Thanks for your time.

2

A serial connection requires 3 wires, RX, TX, and GND.

3

Yep, you also need a GND. Voltage always needs a reference.

Btw, all my (Chinees) Pro Mini's have a diode connected to the serial header side. So it's okay to connect power to both RAW (or in case of a phone charger Vcc on the normal header) and to the serial header at the same time. Because of the diode it will use the charger. But I saw it not part of the original Arduino Pro Mini schematic. Strange, you would expect the Chinees to leave everything they can... One up for the Chinees :smiley:

4

septillion:
Yep, you also need a GND. Voltage always needs a reference.

Btw, all my (Chinees) Pro Mini's have a diode connected to the serial header side. So it's okay to connect power to both RAW (or in case of a phone charger Vcc on the normal header) and to the serial header at the same time. Because of the diode it will use the charger. But I saw it not part of the original Arduino Pro Mini schematic. Strange, you would expect the Chinees to leave everything they can... One up for the Chinees :smiley:

I saw this same topic, and was going to say the same thing, then I looked at the schematic. The kicker is that in the PICTURE on the same page of the Arduino site where they link to that schematic, they show the two diodes that are missing in the schematic!

5

Thanks a lot dmjlambert and septillion! Simply connecting the ground to the adapter worked!
I'm not from electronics field, so I really need to work on fundamentals :smiley:
Thanks again!