Microfire LLC Mod-NTC Datasheet
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This documentation is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International (CC BY-ND).
Release | Date | Description |
1.0.0 | 4/20/2023 | Initial |
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Microfire LLC Mod-NTC Datasheet
MEASURE_TEMP_TASK - Temperature Measurement
BETA_TASK - I²C address change
A module for interfacing with 10K NTC temperature sensors. It has been designed to be flexible and simple to incorporate into new or existing electrical designs.
The Mod-NTC module is a single-sided 25x15 mm 0.8 mm thick PCB with dual castellated/through-hole pins around the east and west edges. It is designed to be usable as a surface mount module as well as in Dual Inline Package (DIP) type format, with the 12 pins on a 2.54mm pitch grid with 0.9mm holes.
Figure 1. Physical dimensions of the module.
The pinout of the module has been designed to provide as many interface options as possible.Figure 2. Pinout of the module.
Pin 1: Probe 1 input. Provides a connection to either wire of the NTC.
Pin 2: Probe 2 input. Provides a connection to the other wire of the NTC.
Pin 3: Not used in this module.
Pin 4: Not used in this module.
Pin 5: Not used in this module.
Pin 6: Not used in this module.
Pin 7: Not used in this module.
Pin 8: Not used in this module.
Pin 9: I²C SCL. Clock line for I2C interface.
Pin 10: I²C SDA. Data line for I2C interface.
Pin 11: VIN. 3.3-volt power supply.
Pin 12: Ground. Ground for the module.
The following figure shows the recommended footprint for mounting the module through reflow processes. It provides for a Class 1 connection (IPC-A-610G § 8.3.4 Castellated Terminations).
It is recommended that the stencil be 8 mils in thickness to ensure enough solder paste can flow into the castellations.
The module is assembled with Chip Quik SMD291SNL50T3 (Sn96.5/Ag3.0/Cu0.5) solder paste, a lead-free paste with a 249-degree Celsius peak reflow temperature. Reflowing the module multiple times can cause malfunction, to avoid the issue, if it is possible, use a lower melting-point temperature solder paste.
Temperature:
When approaching the absolute temperature ratings, it should be noted that the module’s temperature will begin to affect measurements, the extent of which will need to be characterized to the specific environment the module will be deployed in.
Voltage:
The module requires 3.3 volts for proper operation. It can be supplied with less and still communicate through the various peripheral interfaces, but this will not allow the analog circuitry to operate properly. Voltage should not exceed 5.5 volts.
There is no reverse polarity protection on the module.
Isolation is not required for this module.
All modules are designed to be low-power. Power usage has been characterized at two points, idle and active sensor measurement.
The module supports speeds of 10kHz, 100 kHz, 400 kHz, and 1 MHz at 3.3 volts.
The I²C interface uses the following pins:
The module has no pullup resistors on the I²C bus. For reliable communication, appropriate resistors must be chosen for the SDA and SCL lines.
The default address is 0x0C by default. It can be changed through firmware.
Writing is done by sending a start condition followed by the module’s address with the write bit set. The master device then sends data 8 bytes at a time. The first byte received is considered to be the register address. Successive writes will automatically increment the register address by one byte. Transmission is finished with a stop condition.
Reading is done by sending a start condition followed by the module’s address with the read bit set. The master sets the register to read from, then requests data. The device then sends the appropriate number of bytes as determined by the register being read.
Adding the module is a straightforward process.
A suitable power supply must be supplied. Ideal solutions will provide a low-ripple, low-EMI, 3.3 volt supply.
The module operates at the same ground potential as what Pin 11: Ground is connected to, so a low-impedance connection is needed.
An NTC probe that is compatible with the module consists of two wires. This is most commonly provided for with a BNC, SMA, or U.FL connector.
Any unused pins should be left unconnected to any other trace or net.
An NTC (Negative Temperature Coefficient) is a thermistor, a resistor whose resistance changes with temperature. The resistance of NTC will decrease as the temperature increases. The amount the resistance decreases can be related to a constant, commonly referred to as beta, or ß.
NTCs come in various configurations, materials, and specifications. Mod-NTC is intended for room temperature ranges using 10K sensors. The 10K specification signifies the sensor will read 10,000 Ohms at 25 degrees Celsius.
NTC sensors typically come with a value called beta. The beta value is used in a formula to convert the NTC’s output to a temperature value.
Some NTC probes will come with Steinhart-Hart coefficients. They are typically presented as three numbers: A, B, and C. The formula to use the coefficients with Mod-NTC is simple. Call the following function, passing resistance.
float SH_calculation(float _resistance) |
The module’s I²C interface operates similarly to many common I²C sensors. There are several registers that hold values such as temperature or version information. The registers are used to pass information both to the module and the controlling device. Tasks are performed by writing a specified value to a certain register.
All registers are either 1 byte or a float which is 4 bytes formatted as an IEEE 754 32-bit floating point, little-endian. The firmware will allow the registers to be read and written.
Register Name | Value | Type | Description |
HW_VERSION_REGISTER | 0 | byte | Hardware version |
FW_VERSION_REGISTER | 1 | byte | Firmware version |
TASK_REGISTER | 2 | byte | Task register |
STATUS_REGISTER | 3 | byte | Status of measurement |
BETA_REGISTER | 4 | float | Beta value for connected sensor |
TEMP_C_REGISTER | 8 | float | Measured temperature in Celsius |
TEMP_K_REGISTER | 12 | float | Measured temperature in Kelvin |
TEMP_F_REGISTER | 16 | float | Measured temperature in Fahrenheit |
RESISTANCE_REGISTER | 20 | float | Resistance of the temperature sensor in ohms |
BUFFER_REGISTER | 24 | float | Buffer used for passing information |
When a particular value is written to TASK_REGISTER, it starts an operation within the module.
Temperature measurement is performed when MEASURE_TEMP_TASK is written to the TASK_REGISTER register. To read the resulting measurement, you would read the TEMP_C_REGISTER, TEMP_F_REGISTER, TEMP_K_REGISTER or RESISTANCE_REGISTER register.
Task Name | Duration | Value | Description |
MEASURE_TEMP_TASK | 150 ms | 40 | Temperature measurement |
BETA_TASK | 1 ms | 20 | Beta change |
I2C_TASK | 1 ms | 2 | I²C address change |
Starts a temperature measurement.
Register | Description |
None |
Parameter | Description |
TEMP_C_REGISTER | The solution-under-test’s temperature in degrees Celsius. |
TEMP_F_REGISTER | The solution-under-test’s temperature in degrees Fahrenheit. |
TEMP_K_REGISTER | The solution-under-test’s temperature in Kelvin. |
RESISTANCE_REGISTER | The resistance in ohms as measured from the temperature sensor. |
STATUS_REGISTER | An error code for the measurement. Can be one of the following: 0: no error 1: no probe 2: system error |
Changes the device’s beta value.
Register | Description |
BUFFER_REGISTER | Used to temporarily store the new beta value. |
Register | Description |
None |
Changes the device’s I²C address.
Register | Description |
BUFFER_REGISTER | Used to temporarily store the new I²C address. |
Register | Description |
None |
Microfire LLC ㅡ Justin Decker, CEO 61190 Deronda Ave Whitewater, CA 92282 justin@microfire.co | 17 May 2021 Certificate of ComplianceRoHS 3 Directive 2015/863/EUMicrofire LLC certifies to the best of its knowledge and belief that the products listed herein conform with RoHS 3 Directive 2015/863/EU and its subsequent amendments. This declaration further certifies that Microfire LLC has obtained RoHS Certificates of Compliance from each applicable supplier of materials and parts used in the assembly and manufacture of these goods. Modules Mod-EC Mod-pH Mod-ORP Mod-ISO Mod-NTC Development Boards Isolated Dev Board Mod-EVAL Mod-EVAL_ISO Probes Industrial pH Probe Industrial EC Probe Industrial ORP Probe Lab pH Probe Lab EC Probe Lab ORP Probe Justin Decker |
