You can't use your favorite Arduino libraries with this board, but that doesn't mean you can't use your favorite I2C sensor. In this example, you'll connect an AHT20 temperature and humidity sensor the QT Py. Then, you'll upload the example code and open the Serial Monitor to see the temperature and humidity data print out.
The AHT20 is a nice but inexpensive temperature and humidity sensor from the same folks that brought us the DHT22. You can take...
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$4.50
In Stock
This 4-wire cable is a little over 100mm / 4" long and fitted with JST-SH female 4-pin connectors on both ends. Compared with the chunkier JST-PH these are 1mm pitch instead of...
$0.95
In Stock
- Board STEMMA GND to sensor GND (black wire)
- Board STEMMA 3.3V to sensor 3.3V (red wire)
- Board STEMMA SCL to sensor SCL (yellow wire)
- Board STEMMA SDA to sensor SDA (blue wire)
// SPDX-FileCopyrightText: 2024 ladyada for Adafruit Industries
//
// SPDX-License-Identifier: MIT
// https://chat.openai.com/share/5dddee44-3196-4a6b-b445-58ac6ef18501
#include <SoftI2C.h>
extern uint8_t scl_pin;
extern uint8_t sda_pin;
void Wire_begin(uint8_t scl, uint8_t sda);
bool Wire_scan(uint8_t i2caddr);
bool Wire_writeBytes(uint8_t i2caddr, uint8_t *data, uint8_t bytes);
bool Wire_readBytes(uint8_t i2caddr, uint8_t *data, uint8_t bytes);
bool Wire_readRegister(uint8_t i2caddr, uint8_t regaddr, uint8_t *data, uint8_t bytes);
bool readAHT20(float *temperature, float *humidity);
#define AHTX0_I2CADDR_DEFAULT 0x38
void setup() {
while (!USBSerial()); // wait for serial port to connect. Needed for native USB port only
delay(100);
USBSerial_println("CH552 QT Py I2C sensor test");
Wire_begin(33, 34); // set up I2C on CH552 QT Py
USBSerial_print("I2C Scan: ");
for (uint8_t a=0; a<=0x7F; a++) {
if (!Wire_scan(a)) continue;
USBSerial_print("0x");
USBSerial_print(a, HEX);
USBSerial_print(", ");
}
USBSerial_println();
if (! Wire_scan(AHTX0_I2CADDR_DEFAULT)) {
USBSerial_println("No AHT20 found!");
while (1);
}
}
void loop() {
delay(100);
float t, h;
if (!readAHT20(&t, &h)) {
USBSerial_println("Failed to read from AHT20");
}
USBSerial_print("Temp: ");
USBSerial_print(t);
USBSerial_print(" *C, Hum: ");
USBSerial_print(h);
USBSerial_println(" RH%");
}
/*********************** AHT20 'driver */
#define AHTX0_CMD_TRIGGER 0xAC
#define AHTX0_STATUS_BUSY 0x80
bool AHT20_getStatus(uint8_t *status) {
return Wire_readBytes(AHTX0_I2CADDR_DEFAULT, status, 1);
}
bool readAHT20(float *temperature, float *humidity) {
uint8_t cmd[3] = {AHTX0_CMD_TRIGGER, 0x33, 0x00};
uint8_t data[6], status;
uint32_t rawHumidity, rawTemperature;
// Trigger AHT20 measurement
if (!Wire_writeBytes(AHTX0_I2CADDR_DEFAULT, cmd, 3)) {
return false;
}
// Wait until the sensor is no longer busy
do {
if (!AHT20_getStatus(&status)) {
return false;
}
delay(10); // Delay 10ms to wait for measurement
} while (status & AHTX0_STATUS_BUSY);
// Read the measurement data
if (!Wire_readBytes(AHTX0_I2CADDR_DEFAULT, data, 6)) {
return false;
}
// Parse humidity data
rawHumidity = data[1];
rawHumidity = (rawHumidity << 8) | data[2];
rawHumidity = (rawHumidity << 4) | (data[3] >> 4);
*humidity = ((float)rawHumidity * 100.0) / 0x100000;
// Parse temperature data
rawTemperature = (data[3] & 0x0F);
rawTemperature = (rawTemperature << 8) | data[4];
rawTemperature = (rawTemperature << 8) | data[5];
*temperature = ((float)rawTemperature * 200.0 / 0x100000) - 50.0;
return true;
}
/**************************** Wire I2C interface */
void Wire_begin(uint8_t scl, uint8_t sda) {
scl_pin = scl; //extern variable in SoftI2C.h
sda_pin = sda;
I2CInit();
}
bool Wire_scan(uint8_t i2caddr) {
return Wire_writeBytes(i2caddr, NULL, 0);
}
bool Wire_readRegister(uint8_t i2caddr, uint8_t regaddr, uint8_t *data, uint8_t bytes) {
if (!Wire_writeBytes(i2caddr, ®addr, 1)) {
return false;
}
return Wire_readBytes(i2caddr, data, bytes);
}
bool Wire_writeBytes(uint8_t i2caddr, uint8_t *data, uint8_t bytes) {
uint8_t ack_bit;
I2CStart();
ack_bit = I2CSend(i2caddr << 1 | 0); // Shift address and append write bit
if (ack_bit != 0) {
I2CStop();
return false;
}
for (uint8_t i = 0; i < bytes; i++) {
if (I2CSend(data[i]) != 0) {
I2CStop();
return false;
}
}
I2CStop();
return true;
}
bool Wire_readBytes(uint8_t i2caddr, uint8_t *data, uint8_t bytes) {
uint8_t ack_bit;
I2CStart();
ack_bit = I2CSend(i2caddr << 1 | 1); // Shift address and append read bit
if (ack_bit != 0) {
I2CStop();
return false;
}
for (uint8_t i = 0; i < bytes; i++) {
data[i] = I2CRead();
if (i == bytes - 1) {
I2CNak(); // NAK on last byte
} else {
I2CAck(); // ACK on other bytes
}
}
I2CStop();
return true;
}
Confirm that your upload settings match the settings listed here under Tools:
- Board: CH552 Board
- USB Settings: Default CDC
- Upload method: USB
- Clock Source: 16 MHz (internal), 3.3V or 5V
- Bootloader pin: P3.6 (D+) pull-up
For the port, select the COM port that matches your QT Py. It will not be labeled like you may be used to with other boards in the Arduino IDE.
You can confirm that you have the correct port selected by selecting Get Board Info from the Tools menu. This will open the Board Info window. The CH552 QT Py VID is 1209 and the PID is C550.
Page last edited January 22, 2025
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