https://github.com/pedroluisdionisiofraga/esp32-lm75a-driver
Open source driver to LM75A to ESP32 using ESP-IDF framework
https://github.com/pedroluisdionisiofraga/esp32-lm75a-driver
esp-idf esp32 i2c-master
Last synced: 2 months ago
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Open source driver to LM75A to ESP32 using ESP-IDF framework
- Host: GitHub
- URL: https://github.com/pedroluisdionisiofraga/esp32-lm75a-driver
- Owner: PedroLuisDionisioFraga
- Created: 2025-01-17T22:10:59.000Z (4 months ago)
- Default Branch: main
- Last Pushed: 2025-02-14T10:40:58.000Z (3 months ago)
- Last Synced: 2025-03-22T04:12:44.555Z (2 months ago)
- Topics: esp-idf, esp32, i2c-master
- Language: C
- Homepage: https://www.ti.com/product/LM75A?qgpn=lm75a
- Size: 1.56 MB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# LM75A Driver
This is a driver for the LM75A temperature sensor written in C.
## Understand LM75A Basics
- **I2C Addressing**: The LM75A supports 7-bit addressing, where the first four bits are fixed as 1001. The last three bits are configured using pins A2, A1, and A0
- **Registers**:
- **Temperature**: Address 0x00, 9-bit data.
- **Configuration**: Address 0x01, for setting operating modes.
- **$T_{HYST}$ and $T_{OS}$**: Addresses 0x02 and 0x03, for hysteresis and over-temperature settings
- **I2C Operations**: It supports read and write commands, with a pointer register selecting the target data
## `glitch_ignore_cnt`
Filter out noise or glitches on the I2C bus
### Purpose of glitch_ignore_cnt
- I2C lines (SDA and SCL) are vulnerable to noise and signal glitches, especially in electrically noisy environments.
- `glitch_ignore_cnt` defines how many short-duration glitches on the SDA and SCL lines the driver should ignore.
- This filtering improves communication stability and prevents the ESP32 from misinterpreting brief noise as valid signals.
### How It Works
- The driver will ignore pulses on the I2C lines that are shorter than the filter count (glitch_ignore_cnt).
- Higher values provide more noise immunity but may slow down the bus.
- Lower values offer faster communication but are more sensitive to noise.
### Impact on I2C Communication
| Value | Effect |
| ----- | ------ |
| 0 | No glitch filtering (fast but risky) |
| 1–7 (Default) | Moderate filtering for typical use |
| 8–15 | Strong filtering for noisy environments |
## 🔥 $T_{OS}$ (Overtemperature Shutdown Threshold)
The $T_{OS}$ register defines the maximum temperature limit.\
If the measured temperature exceeds this limit, the LM75A triggers an overtemperature alert by activating the OS (Overtemperature Shutdown) pin. Default value is 80°C.
### Purpose
Used for thermal protection to prevent devices from overheating.
### Default Behavior
- **Comparator Mode (Default)**: OS pin stays active until the temperature drops below $T_{HYST}$.
- **Interrupt Mode**: OS pin deactivates after any read operation.
### Register Address: 0x03
### Example
If $T_{OS}$ is set to 80°C, the LM75A will assert the OS pin when the temperature reaches 80°C.
## ❄️ $T_{HYST}$ (Hysteresis Threshold)
The $T_{HYST}$ register sets a lower temperature limit to reset the overtemperature alert after it has been triggered. Default value is 75°C.
### Purpose
- Prevents the sensor from rapidly toggling the OS pin when the temperature hovers around the $T_{OS}$ threshold.
### Register Address: 0x02
### Example
If $T_{OS}$ is set to 80°C and $T_{HYST}$ is set to 75°C:
- The OS pin will be triggered when the temperature reaches 80°C.
- The OS pin will only deactivate when the temperature drops below 75°C.
## 🔄 How $T_{OS}$ and $T_{HYST}$ Work Together
This hysteresis prevents false triggers caused by small temperature fluctuations.
1. Rising Temperature:
- If T > $T_{OS}$, the OS pin is activated.
2. Falling Temperature:
- The OS pin remains active until the temperature drops below $T_{HYST}$.
## ⚙️ Configuration Register
The Configuration Register allows you to configure the operating mode and other settings of the LM75A sensor.
### Purpose
- Configure the sensor's operating mode (Comparator or Interrupt).
- Enable or disable the OS pin.
### Register Address: 0x01
### Configuration Bits
| Bit | Name | Description |
| --- | ---------- | ------------------------------------------------ |
| 7 | OS_POL | OS polarity (0: Active low, 1: Active high) |
| 6 | OS_F_QUE | OS fault queue (00: 1 fault, 01: 2 faults, 10: 4 faults, 11: 6 faults) |
| 5 | OS_COMP_INT| OS mode (0: Comparator, 1: Interrupt) |
| 4 | SHUTDOWN | Shutdown mode (0: Normal, 1: Shutdown) |
| 3-0 | Reserved | Reserved bits |
### Example
To set the sensor to Interrupt mode with active high polarity and 4 faults queue:
- Write `0b01001000` to the Configuration Register.
## 🌡️ Temperature Register
The Temperature Register holds the current temperature reading from the LM75A sensor.
### Purpose
- Read the current temperature in Celsius.
### Register Address: 0x00
### Data Format
- The temperature data is a 9-bit two's complement value.
- The MSB is the most significant byte, and the LSB is the least significant byte.
- The temperature is represented in 0.5°C increments.
### Example
To read the temperature:
- Read 2 bytes from the Temperature Register.
- Combine the bytes and shift right by 7 to get the 9-bit value.
- Multiply by 0.5 to get the temperature in Celsius.
## Example of Usage
```c
#include
#include
#include
#include
#include
#include "lm75a.h"
static const char *TAG = "MAIN";
/* ------------------------------------------------------------------
* Existing or newly introduced #defines in main
* Adjust these to match your board / wiring
* ------------------------------------------------------------------ */
#define I2C_MASTER_SDA_IO 21
#define I2C_MASTER_SCL_IO 22
#define I2C_MASTER_FREQ_HZ 400000
#define LM75A_I2C_ADDR 0x48
#define LM75A_OS_PIN 23
static volatile uint8_t interrupt_count = 0;
static volatile uint8_t last_counter = 0;
// OS interrupt handler
static void os_interrupt_handler(void *arg)
{
// Toggle LED (example on GPIO2)
gpio_set_level(GPIO_NUM_2, !gpio_get_level(GPIO_NUM_2));
// Increment interrupt counter
interrupt_count++;
}
void app_main(void)
{
// Configure an LED as output on GPIO2 (example)
gpio_config_t led_conf = {.pin_bit_mask = (1ULL << GPIO_NUM_2),
.mode = GPIO_MODE_OUTPUT,
.pull_up_en = GPIO_PULLUP_DISABLE,
.pull_down_en = GPIO_PULLDOWN_DISABLE,
.intr_type = GPIO_INTR_DISABLE};
gpio_config(&led_conf);
// 1) Simplified LM75A init if you have a function like this
lm75a_t *lm75a = lm75a_create((lm75a_config_t){
.i2c_port = I2C_NUM_0,
.master_sda_pin = I2C_MASTER_SDA_IO,
.master_scl_pin = I2C_MASTER_SCL_IO,
.os_pin = LM75A_OS_PIN,
.i2c_frequency = I2C_MASTER_FREQ_HZ,
.address = LM75A_I2C_ADDR,
});
lm75a_status_t status;
status = lm75a->init(lm75a);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to initialize LM75A: %s", lm75a_status_to_string(status));
return;
}
// 2) Optional: set an interrupt on the OS pin
status = lm75a->set_os_interrupt(lm75a, os_interrupt_handler, NULL);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to set OS interrupt: %s", lm75a_status_to_string(status));
return;
}
// 3) Set THYST
status = lm75a->set_thys(lm75a, -26, true);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to set THYST: %s", lm75a_status_to_string(status));
return;
}
// 3.5) Read THYST
float thys;
status = lm75a->get_thys(lm75a, &thys);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to get THYST: %s", lm75a_status_to_string(status));
return;
}
ESP_LOGI(TAG, "THYST: %.1f°C", thys);
// 4) Set TOS
status = lm75a->set_tos(lm75a, 14, false);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to set TOS: %s", lm75a_status_to_string(status));
return;
}
// 4.5) Read TOS
float tos;
status = lm75a->get_tos(lm75a, &tos);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to get TOS: %s", lm75a_status_to_string(status));
return;
}
ESP_LOGI(TAG, "TOS: %.1f°C", tos);
// 5) Set OS mode
status = lm75a->set_os_mode(lm75a, LM75A_OS_INTERRUPT_MODE);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to set OS mode: %s", lm75a_status_to_string(status));
return;
}
// 5) Get and log product ID
// .
// .
// .
// 5) Main loop reading temperature
while (1)
{
float temperature;
status = lm75a->read_temperature(lm75a, &temperature, LM75A_SCALE_CELSIUS);
if (status != LM75A_OK)
{
ESP_LOGE(TAG, "Failed to read temperature: %s", lm75a_status_to_string(status));
}
else
{
ESP_LOGI(TAG, "Temp: %.2f°C | Interrupt Count: %d", temperature, interrupt_count);
}
vTaskDelay(pdMS_TO_TICKS(2000));
if (interrupt_count > last_counter)
{
last_counter = interrupt_count;
ESP_LOGW(TAG, "Interrupt detected! Counter: %d", interrupt_count);
ESP_LOGW(TAG, "GPIO2: %d", gpio_get_level(GPIO_NUM_2));
}
}
// 7) Clean up (unreachable in this loop example)
lm75a_destroy(lm75a);
}
```
## Future Works
- [ ] Test with negative temperature values, i.e., submit the sensor to a cold environment and verify if the measures (read_temperature) and the triggers ($T_{OS}$, $T_{HYST}$) are working properly.
## References
1. [LM75A open source - 13xiaobang](https://github.com/13xiaobang/esp32_lm75a/tree/master/main)
2. [LM75A open source - UncleRus](https://github.com/UncleRus/esp-idf-lib/tree/master/components/lm75)