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191 lines
6.4 KiB
Markdown
191 lines
6.4 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/MAX31850/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/MAX31850/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/MAX31850/issues)
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[](https://github.com/RobTillaart/MAX31850/blob/master/LICENSE)
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[](https://github.com/RobTillaart/MAX31850/releases)
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[](https://registry.platformio.org/libraries/robtillaart/MAX31850)
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# MAX31850
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Arduino library for the MAX31850 / MAX31851 thermocouple sensor.
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## Description
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**WARNING EXPERIMENTAL** needs more testing (no hardware yet).
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(feedback welcome)
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his MAX31850 library is not a full featured library for the MAX31850 family.
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The MAX31850/1 is a Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converter.
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The MAX31850/1 supports K-, J-, N-, T-, S-, R-, and E-type thermocouples. (to be tested).
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The library supports both the MAX31850 and MAX31851 but is limited to one sensor per pin.
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The only feature the class supports is the asynchronous reading of the temperature.
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This allowed the class to be both minimal in size and non-blocking.
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In fact the class has no support for a synchronous read in one call.
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This choice will teach people how to work in a non-blocking way from the start.
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Finally this library will probably make it easier to use a MAX31850 with processing
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boards or IC's with small memory footprint.
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The MAX31851 is (for now) functional identical to MAX31850.
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#### Related
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- https://github.com/RobTillaart/MAX6675
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- https://github.com/RobTillaart/MAX31850
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- https://github.com/RobTillaart/MAX31855_RT
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## Hardware connection
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```
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// PROCESSOR MAX31850 THERMOCOUPLE
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// +---------------+
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// GND 1 | o o | T+
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// DATA 2 | o |
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// VCC 3 | o o | T-
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// | |
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// | oooo |
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// +---------------+
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// 4 address pins.
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```
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This library supports only one MAX31850 per Arduino/ MCU IO pin.
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#### Pull up resistor
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Connect a pull-up resistor 4.7 KOhm between DATA (pin 3) and VCC (pin 2).
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When the wires are longer this resistor needs to be smaller.
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An **indicative** table for pull up resistors, (E12 series), to get started.
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Note: thicker wires require smaller resistors (typically 1 step in E12 series)
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| Length | 5.0 Volt | 3.3 Volt |
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|----------------:|-----------:|-----------:|
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| 10cm (4") | 10K0 | 6K8 |
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| 20cm (8") | 8K2 | 4K7 |
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| 50cm (20") | 4K7 | 3K3 |
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| 100cm (3'4") | 3K3 | 2K2 |
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| 200cm (6'8") | 2K2 | 1K0 |
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| 500cm (16'8") | 1K0 | \* |
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| longer | \* | \* |
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\* = no info, smaller
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## Interface
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```cpp
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#include "MAX31850.h"
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```
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#### Constructor
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- **explicit MAX31850(OneWire \* oneWire)** constructor.
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- **bool begin(uint8_t retries = 3)** initialize the library.
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Returns true if addresses are found.
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Nr of retries can be adjusted if needed, default 3.
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- **bool getAddress(uint8_t \* buffer)** get the address if found.
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#### Read the sensor
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- **void requestTemperatures(void)** Asynchronous request to start conversion.
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- **bool isConversionComplete(void)** CHeck if requested conversion is done.
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- **float read(void)** read the data from the sensor.
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Returns the temperature of the thermoCouple as this is most often needed.
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- **float getTempTC(void)** returns temperature of the ThermoCouple from cache.
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One must call **read()** again to get new measurements.
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- **float getTempInternal(void)** returns internal temperature from cache.
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One must call **read()** again to get new measurements.
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#### Other
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- **uint8_t getAddressPins()** binary form of the 4 address bits. 0x00..0x0F.
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- **uint8_t getErrorCode()** get the internal error code. See below.
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- **bool setTypeTC(char typeTC)** typeTC is one char from E J K N R S T
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- **uint8_t getTypeTC()** returns the current TC type.
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## Types of thermocouples
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The MAX31850 comes in MAX31850E.. MAX31850T types reflecting the version of TC to use.
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| Sensor type | SC in µV/°C | Temp Range in °C | Material | notes |
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|:-------------:|:--------------|:-------------------|:----------------------------|:------------|
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| E_TC | 76.373 | -270 to +1000 | Constantan Chromel |
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| J_TC | 57.953 | -210 to +1200 | Constantan Iron |
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| K_TC | 41.276 | -270 to +1372 | Alumel Chromel | most used |
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| N_TC | 36.256 | -270 to +1300 | Nisil Nicrosil |
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| R_TC | 10.506 | -50 to +1768 | Platinum Platinum/Rhodium |
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| S_TC | 9.587 | +50 to +1768 | Platinum Platinum/Rhodium |
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| T_TC | 52.18 | -270 to +400 | Constantan Copper |
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(MAX31851 idem)
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## Error codes
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| name | value |
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|:--------------------------|:-------:|
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| MAX31850_OK | 0 |
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| MAX31850_ERR_SHORT_OPEN | 1 |
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| MAX31850_ERR_SHORT_GND | 2 |
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| MAX31850_ERR_SHORT_VDD | 4 |
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## Future
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#### Must
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- improve documentation
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- get hardware to test (sponsors welcome)
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- test on different platforms
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#### Should
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- investigate different thermocouples
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- test with different platforms
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- has the MAX31851 special features to implement?
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#### could
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- extend error handling
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- expand to multi sensor per pin.
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- first get one sensor working
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- investigate range checking on type TC
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- need setType() and more.
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- need lower upper range = int16_t will do.
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- add CRC check
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- + error code
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#### Wont
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## Support
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If you appreciate my libraries, you can support the development and maintenance.
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Improve the quality of the libraries by providing issues and Pull Requests, or
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donate through PayPal or GitHub sponsors.
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Thank you,
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