Pinout diagram corrections

[lemmingDev]

Hi

The pinout diagram should be updated to reflect that pins 32 and 33 are only capable of output (GPO), and pins 34, 35, 36 and 39 are only capable of input (GPI).

See this official Espressif document here:
http://esp32.net/images/Espressif/ESP-WROOM-03/Espressif_ESP-WROOM-03_Pinout.pdf

Also, touch inputs T1 (pin 0 - USB serial chip) and T6 (pin 14 - LED) have resistors connected to them on the T-Beam and won't work for touch, so those labels should be removed.

Here is a file you could use

[Skipper-is]

Are any of the pins set up for reading battery level?

[lemmingDev]

Pin 35 I think

So something like:

float vBat;
vBat = analogRead(35) * 2.0 * (3.3 / 4096.0) * 1100/1000;
Serial.print("Battery voltage: ");
Serial.print(vBat);
Serial.println("V");

There is also a more precise way of using a factory set value
Will check how it's done again and let you know

[lemmingDev]

This sketch for the TTGO T-Display, among other things, shows how to use the e-fuse ESP_ADC_CAL_VAL_EFUSE_VREF value to get the accurate battery reading

https://github.com/Xinyuan-LilyGO/TTGO-T-Display/blob/master/TFT_eSPI/examples/FactoryTest/FactoryTest.ino

Let me know if you have trouble deciphering it to use

[lemmingDev]

This sketch sets up a Classic BT serial port that you can monitor for a voltage readout (9600 baud)
You'll need to pair your PC with the BT device called ESP32test after uploading the code and then open the new serial port created (there are 2 ports created, but only one will have the data - for me it was the port with the lower number)

You'll see that it goes up when the USB is plugged in, and down when the USB is removed

The vref stored in the efuses for the board I have on hand is exactly 1100, so I'm not sure whether my board was spot on, or they didn't bother setting it on my board.

#include "BluetoothSerial.h"
#include "esp_adc_cal.h"

#define ADC_PIN             35  //ADC_PIN is the ADC pin the battery is connected to through a voltage divider

int vref = 1100;                //Default value. We'll get a more accurate value from the efuses
uint64_t timeStamp = 0;

BluetoothSerial SerialBT;

void showVoltage()
{
    if (millis() - timeStamp > 1000) {
        timeStamp = millis();
        uint16_t v = analogRead(ADC_PIN);
        float battery_voltage = ((float)v / 1024.0) * 2.0 * 3.3 * (vref / 1000.0);
        String voltage = "Voltage :" + String(battery_voltage) + "V\n";
        SerialBT.println(voltage);
    }
}

void setup()
{
    SerialBT.begin("ESP32test"); //Bluetooth device name

    adcAttachPin(ADC_PIN);
    adcStart(ADC_PIN);
    analogReadResolution(10); // Default of 12 is not very linear. Recommended to use 10 or 11 depending on needed resolution.

    esp_adc_cal_characteristics_t adc_chars;
    esp_adc_cal_value_t val_type = esp_adc_cal_characterize((adc_unit_t)ADC_UNIT_1, (adc_atten_t)ADC1_CHANNEL_6, (adc_bits_width_t)ADC_WIDTH_BIT_12, 1100, &adc_chars);
    //Check type of calibration value used to characterize ADC
    if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF) {
        SerialBT.printf("eFuse Vref:%u mV", adc_chars.vref);
        vref = adc_chars.vref;
    } else if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP) {
        SerialBT.printf("Two Point --> coeff_a:%umV coeff_b:%umV\n", adc_chars.coeff_a, adc_chars.coeff_b);
    } else {
        SerialBT.println("Default Vref: 1100mV");
    }
    SerialBT.println();
}

void loop()
{
  showVoltage();
}

[BrugerX]

Hi

The pinout diagram should be updated to reflect that pins 32 and 33 are only capable of output (GPO), and pins 34, 35, 36 and 39 are only capable of input (GPI).

See this official Espressif document here: http://esp32.net/images/Espressif/ESP-WROOM-03/Espressif_ESP-WROOM-03_Pinout.pdf

Also, touch inputs T1 (pin 0 - USB serial chip) and T6 (pin 14 - LED) have resistors connected to them on the T-Beam and won't work for touch, so those labels should be removed.

Here is a file you could use

Hello Lemming,

I am trying to use the T-Beam to read a soil moisture sensor. I have used a voltage divider circuit with R1 being 10k and R2 being 20k. I get a reading from the output of the sensor of approx. 3.6V and approx. 2.4V from the output of the voltage divider.

However, both pin 33 and pin 35 read 0 value using the Arduino analogRead with the 2.4V. Using the 3.6V directly I do get a result, however they're very different, with pin 33 reading approx. 1100 and pin 35 reading approx. 2800.

Do you have any idea, why this is happening?