AB-01 v1.2 and photoresistor data from analogRead ADC pin

#1

I use AB-01 boards ver 1.2
I need to check light level so I read photoresistor data.
Circuit is standard, like on the picture:

image
image.jpg2336×1243 485 KB

just one modification - I put power to photoresistor from GPIO pin - I suppose there is 3.3v.
All the rest the same - 10K resistor and ADC pin.

I use a lot this circuit with another device - Moteino - I also power photoresitor from GPIO 3.3v - and I receive from photoresistor data via analogRead() function - the values around 750 in my test conditions.

I noticed that on AB-01 boards ver 1.2 when you read ADC with connected photoresistor in this standard circuit - it shows data which much differ - values around 3500.
So again - same circuit, same components, just different device - and analogRead function show different data.
code pretty simple:

#include "LoRaWan_APP.h"
// light sensor >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
//HTCC-AB01
//https://github.com/HelTecAutomation/CubeCell-Arduino/blob/master/variants/CubeCell-Board/pins_arduino.h

#define LIGHT_PWR P0_2 // GPIO0
#define LIGHT P2_3 // ADC
// light sensor <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

void setup()
{
    Serial.begin(9600);
    pinMode(LIGHT_PWR, OUTPUT);
        digitalWrite(LIGHT_PWR, LOW);
    pinMode(LIGHT, INPUT);
}

void loop() {
  digitalWrite(LIGHT_PWR, HIGH);
  int light = analogRead(LIGHT);
  Serial.print(F("light: ")); Serial.println(light);
  digitalWrite(LIGHT_PWR, LOW);
  delay(2000);
}

and I can see in output:

light: 3438
light: 3371
light: 3584
light: 3559
light: 3753
light: 3521

is it normal behavior and I should just consider to take this in mind and correct my code for CubeCells boards? or Im doing something wrong while reading analog values from ADC pin this way?

#2

The readings you get from ADCs on different platforms will invariably depend on the sensitivity (the maximum voltage that can be measured) and resolution (the range of reported values) of the respective ADCs. The ADC on the CubeCell ASR6502 processor has 12 bit (0…4095) resolution and accepts a maximum voltage of 2.4V—higher voltages can be measured using an appropriate voltage divider on the input.

#3

thank you.
As I found out - on my Moteino devices - it is 10bit ADC with 0-1023 values.
So seems in my case its better to calibrate new results of values from Cubecell.