PiSensors is a C source library for reading sensors on the Raspberry Pi
GPIO header under piAROS (Raspberry Pi 3 / 3B+ / 4).

Version 0.4 supports:
 - DHT11, DHT22 / AM2302   temperature, humidity (any GPIO)
 - DS18B20                 temperature, several sensors on one pin
                           (1-Wire, any GPIO; also DS18S20, DS1822)
 - BME280                  temperature, humidity, pressure (I2C)
 - BMP280                  temperature, pressure (I2C)
 - OLED display 0.96" 128x64, SSD1306 (also SH1106) (I2C)

It is a source / link library, not a system .library: there is nothing
to install. Add the source files to your project, or link the included
libpisensors.a, and read a sensor with a few lines of C:

DHT11 / DHT22 on GPIO4 (header pin 7):

    struct PiDhtReading d;
    char t[16], h[16];

    pig_open();
    if (pidht_read(4, 0, &d) == PIG_OK)
        printf("DHT%d: %s C, %s %%n", d.type,
               pig_tenths_to_str(t, d.temp10),
               pig_tenths_to_str(h, d.hum10));

All DS18B20 sensors on GPIO4:

    UBYTE rom[8][8];
    struct PiDsReading s;
    int i, n = pids_search(4, 0, rom, 8);

    for (i = 0; i < n; i++)
        if (pids_measure(4, 0, rom[i], &s) == PIG_OK)
            printf("%s Cn", pig_tenths_to_str(t, s.temp10));

BME280 / BMP280 on the I2C bus:

    struct PiBme280 bme;
    struct PiBme280Reading r;
    char p[16];

    if (pibme280_open(&bme, PIBME280_ADDR_AUTO, 0) == PIG_OK &&
        pibme280_read(&bme, &r) == PIG_OK)
        printf("%s hPan", pig_tenths_to_str(p, r.pres10));

Text on an OLED display:

    struct PiOled o;

    if (pioled_open(&o, PIOLED_ADDR_AUTO, 0) == PIG_OK)
    {
        pioled_text(&o, 0, 20, "Hello", 3, 1);
        pioled_update(&o);
    }
    pii2c_close();

DHT11 / DHT22 driver (pidht):
 - automatic sensor type detection, 2-second read guard
 - clear error codes; on a timeout it tells where the reading stopped
 - the data pin is only ever driven low, never high

DS18B20 driver (pids18b20):
 - finds all sensors on one pin by their 64-bit numbers (ROM codes)
 - CRC check of every reading; the 85.0 C power-up value is recognised
   and measured again
 - interrupts are disabled only inside one bit (max. 75 us), never for
   a whole reading; pids_start() lets a window program measure in the
   background instead of waiting 750 ms
 - the data pin is only ever driven low, never high

BME280 / BMP280 driver (pibme280):
 - tells a BMP280 (no humidity) from a BME280 by its chip ID - cheap
   boards are often mixed up by sellers
 - finds the sensor at 0x76 or 0x77 by itself
 - Bosch's integer compensation formulas, checked against the datasheet
 - forced mode: the sensor sleeps between readings and does not warm up

OLED display driver (pioled):
 - SSD1306 0.96" and SH1106 1.3", address 0x3C / 0x3D found by itself
 - text in a 5x7 font in several sizes (with degree sign), pixels,
   lines, rectangles; picture rotated by 180 degrees on request
 - powered from 3.3 V - no level shifter needed

I2C bus (pii2c), usable for your own I2C drivers:
 - hardware I2C controller on GPIO2/3 (header pins 3 and 5)
 - checks that SDA/SCL are not stuck low before taking the pins,
   gives them back as they were when closed
 - automatic retries and bus recovery after a disturbance
 - only one program can use the bus at a time, so two programs cannot
   garble each other's transfers; the bus is freed when a program ends

GPIO layer (pigpio), usable for your own drivers:
 - pin access with safety checks: only GPIO 2..27 can be changed, pins
   used by UART / I2C / SPI are refused unless you pass PIG_FORCE
 - microsecond timer that also works with interrupts disabled
 - board detection; Raspberry Pi 5 is refused (GPIO is in the RP1 chip)

All values are integers (temperature 215 = 21.5 C, pressure 10133 =
1013.3 hPa) - no floating point needed.

Included, as source and ready-built:
 - SensorPins   graphical demo (Zune): shows which header pins to use
                for a DHT, DS18B20 or BME/BMP280, warns about wrong
                choices, reads the sensor live and can show the values
                on an OLED display too
 - DHTRead      reads a DHT11 / DHT22 (Shell)
 - DSRead       finds and reads DS18B20 sensors (Shell)
 - BMERead      reads a BME280 / BMP280 (Shell)
 - I2CScan      lists the devices on the I2C bus (Shell)
 - OLEDDemo     small weather station: BME280 values on an OLED (Shell)
 - libpisensors.a, build.sh for the AROS cross compiler
 - manual.txt   API reference, wiring, troubleshooting

Planned: SCD40 (CO2), OLED preview in SensorPins.

Connecting sensors is done at your own risk. Read the safety chapter in
manual.txt before wiring anything. GPIO pins are 3.3 V only - never
connect 5 V to a GPIO pin. A bare DS18B20 or the waterproof cable
version needs a 4.7 kOhm resistor between DATA and 3.3 V.

Copyright (c) 2026 rhun. MIT licence. Provided "as is", without
warranty of any kind.