Olny one pin for input and output together

Other Hardware General Electronics
1

Hello, I have only one pin on MCU and sometimes will be set as INPUT and sometimes as OUTPUT. Two different software, but I need one hardware. Any idea how to make a schematic?

When software for INPUT will be used, pin on MCU will be connect directly to GROUND during switch.
When software for OUTPUT will be used, connected will be LED diode with maximum current 3 mA.

mcu
mcu587×414 2.64 KB

2

Welcome to the forum

Why ?
Which Arduino board and what are the other pins used for ?

Do you have a question ?

3

Does your MCU have open drain outputs?
What is the Vf of the LED?

4

Assuming you are using an Arduino...

A digital GPIO pin can be used for input or output, and you can switch function inside a sketch. For example I have a circuit that uses a small coil to sense a passing magnet which is then changed to an output so current can be pulsed through the coil to exert a force. In your circuit above and assuming a 5V Arduino, the LED might drop ~1.3v so for 3mA you would need a resistor in series with the LED of (5 - 1.3)/0.003 = 3.7/0.003 = ~1200 ohms.

5

With the circuit shown you will eventually fry your Arduino, you need a current limiting resistor as recommended by jhaine. Also wire it with the resistor from 5V to the anode of the LED, the Cathode connected to the port pin. Your switch will remain the same. The difference is when pressing the button the LED will light and your Arduino will live again for another project. Note you will also have to change the software so the pin goes low to turn on the LED.

6

To address your requirement of using a single pin on the MCU as both an input and an output, you can employ a simple circuit with a pull-down resistor and an LED. Here's a schematic that should meet your needs:

   +5V
    |
    R1
    |
   MCU
    |
    |
    |
  [Pin]
    |
    R2
    |
    |
    LED
    |
  GROUND

Here's how the circuit works:

  • When the pin is set as an input, it is not actively driving the line. The pull-down resistor (R1) connects the pin to ground, ensuring a clear low signal when the switch is closed.
  • When the pin is set as an output, it can actively drive the line. The LED (with a maximum current of 3 mA) is connected in series with a current-limiting resistor (R2) to prevent excessive current flow and protect the LED from burning out.
  • The resistor values for R1 and R2 will depend on the specific characteristics of your MCU and the LED you are using. You can select appropriate resistor values based on the voltage levels and currents specified in your MCU's datasheet and the LED's specifications.

Remember to consider the voltage levels and current capabilities of your MCU to ensure the circuit operates within its limits.

7

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