FTDI Debugger

[TeslaIaint]

I have set up a breadboard arduino  (ATmega 328 with Arduino Uno Optiboot) much like the picture below according to this tutorial: http://arduino.cc/en/Main/Standalone

In order to program, I wired up the FTDI Basic Breakout https://www.sparkfun.com/products/9716 like this:

ftdi                     arduino
5v         -------->      5v
GND      -------->     GND
TX         -------->     RX
RX         -------->     TX
DTR (RST)   ----->    Reset     must connect through a .1uF ceramic cap

I uploaded this code and it works fine.

Code: [Select]



int led = 9;

// the setup routine runs once when you press reset:
void setup() {                
 // initialize the digital pin as an output.
 pinMode(led, OUTPUT);
 Serial.begin(9600);  
}

// the loop routine runs over and over again forever:
void loop() {
 digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
 Serial.println("test");
 delay(1000);               // wait for a second
 digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
 delay(1000);               // wait for a second
}


For future use, I would like to use a power supply for the chip and inputs/outputs other than the USB power supplied by the FTDI breakout board, but I would like to use the FTDI breakout board connected to my computer for debugging. How can I connect the FTDI board without the conflicting power issues?

[retrolefty]

For future use, I would like to use a power supply for the chip and inputs/outputs other than the USB power supplied by the FTDI breakout board, but I would like to use the FTDI breakout board connected to my computer for debugging. How can I connect the FTDI board without the conflicting power issues?

Simple enough, just don't connect the 5 volt or 3.3 volt terminals of the FTDI module to your breadboard, just the ground terminals, DTR, Tx and Rx terminals. What you can do to help with conflict like when your standalone 328p and external circuitry is being powered up with a battery or other independent voltage source but the FTDI module is not plugged into the PC, is to use two series 1K ohm resistors in each of the Rx and Tx signals going to your standalone. That will prevent any 'back door' current flow in that situation.

Lefty

[TeslaIaint]

What you can do to help with conflict like when your standalone 328p and external circuitry is being powered up with a battery or other independent voltage source but the FTDI module is not plugged into the PC, is to use two series 1K ohm resistors in each of the Rx and Tx signals going to your standalone. That will prevent any 'back door' current flow in that situation.

Thanks Lefty. I previously just tried unplugging the 5v from the FTDI, but my "test power" led was still dimly lit. You say that a 1K resistor will work from RX of FTDI to TX of uC and another series 1K resistor from TX of FTDI to RX of uC while the FTDI is connected to the PC and the rest of the board is under external power? I just want to make sure I understand you.

[retrolefty]

What you can do to help with conflict like when your standalone 328p and external circuitry is being powered up with a battery or other independent voltage source but the FTDI module is not plugged into the PC, is to use two series 1K ohm resistors in each of the Rx and Tx signals going to your standalone. That will prevent any 'back door' current flow in that situation.

Thanks Lefty. I previously just tried unplugging the 5v from the FTDI, but my "test power" led was still dimly lit. You say that a 1K resistor will work from RX of FTDI to TX of uC and another series 1K resistor from TX of FTDI to RX of uC while the FTDI is connected to the PC and the rest of the board is under external power? I just want to make sure I understand you.

Yes, that is correct. And by the way the standard arduino board design is to isolate the USB serial converter's send and rec lines with 1K ohm resistors. That is mostly so that it's somewhat possible to use pins 0 and 1 with user external components if not needing or using serial commands, but the isolation also works for having different or no power on the FTDI's module.

Lefty

[TeslaIaint]

I disconnected the 5v from the FTDI cable and put the 1k ohm resistors in series with the rx-tx and tx-rx, but am still getting 1.9 V to the 5V rail. Any other ways to get rid of that? Or will it not damage my chip or components with a separate battery supply to the circuit?

[xl97]

I leave my FTDI cables plugged into GND, RX, TX (no +5v).. and power my boards from my PSU all the time... especially when debugging..

or because my custom Arduino based boards have a +5v voltage regulator.. which needs more than +5 to power it).. so I power externally.. but I still want my FTDI cable connected (RX/TX/GND) so I can see whats going on in my serial monitor.. or do serial communications..etc..


I havent tried lefty's suggestion on the resistors.. but probably something I would benefit from doing

[TeslaIaint]

or because my custom Arduino based boards have a +5v voltage regulator.. which needs more than +5 to power it).. so I power externally.. but I still want my FTDI cable connected (RX/TX/GND) so I can see whats going on in my serial monitor.. or do serial communications..etc..

Yea that's the only reason I would like the FTDI cable connected as well, and I'll also be using a 5V regulator.  Good to know it isn't letting the smoke out. Thanks