Read analog input from Arduino Uno Wifi Wire/TWI/I2C pins (A4 & A5)

Question

I recently got an Arduino Uno Wifi (flashed it with the Wifilink firmware to support UDP) and I have created a simple sketch to read analog values from a flex sensor.

I am using the code below (copy paste from the official website)

const int FLEX_PIN = A4; // Pin connected to voltage divider output

// Measure the voltage at 5V and the actual resistance of your
// 47k resistor, and enter them below:
const float VCC = 4.98; // Measured voltage of Ardunio 5V line
const float R_DIV = 47500.0; // Measured resistance of 3.3k resistor

// Upload the code, then try to adjust these values to more
// accurately calculate bend degree.
const float STRAIGHT_RESISTANCE = 37300.0; // resistance when straight
const float BEND_RESISTANCE = 90000.0; // resistance at 90 deg

void setup() {
  Serial.begin(9600);
  pinMode(FLEX_PIN, INPUT);
}

void loop() {
  // Read the ADC, and calculate voltage and resistance from it
  int flexADC = analogRead(FLEX_PIN);
  float flexV = flexADC * VCC / 1023.0;
  float flexR = R_DIV * (VCC / flexV - 1.0);
  Serial.println("Resistance: " + String(flexR) + " ohms");
  // Use the calculated resistance to estimate the sensor's
  // bend angle:
  float angle = map(flexR, STRAIGHT_RESISTANCE, BEND_RESISTANCE, 0, 90.0);
  Serial.println("Bend: " + String(angle) + " degrees");
  Serial.println();
  delay(500);
}

The code does not work in the Arduino Uno Wifi: it does not show any change in the bend degrees. However, it works in another Arduino Uno I have for testing.

Also I made a test and I found out that pins 4 and 5 in Arduino Uno Wifi produce current for some reason even with an empty script, capable of lighting a LED (while pins 0,1,2,3 do not light it up).

The same applies for the values for the sensors. For example if I put the flex sensor in analog pin 0 then the values change when I bend it (e.g. 362 read not bend and 600 bend, which is fine).

On the other hand when I put the pin of the sensor in A4 or A5 there is a change from 1023 (starting value) to 982 and it won't change no matter if I bend the sensor.

I was recently informed that those pins are Wire/TWI/I2C pins. Is there any way i can read analog input from those pins?

Also posted in Arduino forums link

Did not know that will do – user2713459 Nov 07 '17 at 08:17 — user2713459, Nov 07 '17 at 08:17
edited with the link added – user2713459 Nov 07 '17 at 09:53 — user2713459, Nov 07 '17 at 09:53

Juraj · Accepted Answer · 2018-01-07T03:27:14.193

0

'WiFi' is connected to those pins.

pins A4 and A5 are Wire/TWI/I2C pins and there is the additional UART SC16IS750 connected to which the esp8266 is connected on Uno WiFi

edited Jan 07 '18 at 03:27

answered Nov 07 '17 at 05:12

Juraj

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Thank you for your answer i just edited the post, is there any way to read analog input from those pins ? – user2713459 Nov 07 '17 at 10:21
1

the SC16IS750 is wired on board and whatever you do, the line and connection will disturb the analog reading. use another analog pin or if you don't want to use the wifi capability, buy a regular Uno. – Juraj Nov 07 '17 at 12:44

Read analog input from Arduino Uno Wifi Wire/TWI/I2C pins (A4 & A5)

1 Answers1