SHT30NopI2CTemperatureAndHumiditySensor < IoT_Course

---+ The SHT30 !I2C Temperature and Humidity Sensor
---++ Introduction

The SHT30 is a temperature and humidity sensor that communicates over the !I2C bus. Typical accuracy for temperature is +- 0.1 °C and +- 1.5% relative humidity. Sensirion, the company behind the SHT30 supplies a series of documents including the data sheet, several application notes and sample code, written in C for the !STM32F10x micro-controller. You can find them at [[https://www.sensirion.com/en/download-center/humidity-sensors/digital-humidity-sensors-for-various-applications/][https://www.sensirion.com/en/download-center/humidity-sensors/digital-humidity-sensors-for-various-applications.]]

There is also [[https://github.com/rsc1975/micropython-sht30][a SHT30 driver written for !MicroPython on the ESP8266]] but unfortunately it did not work on the ESP32 out of the box. Making it work for the ESP32 is not too difficult however. This is the subject of an exercise on the SHT30 ( [[The I2C bus and the SHT30 Temperature and Humidity Sensor]] ). Since the SHT30 driver only implements a small subset of the SHT30 functionality, I developed a driver called !SHT3X translating the Sensirion code into !MicroPython and taking over some of the SHT30 code.

Here is a list of functions, their command codes and if they are implemented in the SHT30 driver:

| Function | Repeatability | measurement per s | Clock Stretching | Command Code | Implemented in SHT30 driver |
| Single shot data acquisition | High | | enabled | 0x2C06 | no |
| ^ | Medium | ^ | ^ | 0x2C0D | no |
| ^ | Low | ^ | ^ | 0x2C10 | no |
| ^ | High | ^ | disabled | 0x2400 | yes |
| ^ | Medium | ^ | ^ | 0x240B | no |
| ^ | Low | ^ | ^ | 0x2416 | no |
| Continuous data acquisition | High |  0.5  | disabled | 0x2032 | no |
| ^ | Medium | ^ | ^ | 0x2024 | no |
| ^ | Low | ^ | ^ | 0x202F | no |
| ^ | High |  1  | ^ | 0x2130 | no |
| ^ | Medium | ^ | ^ | 0x2120 | no |
| ^ | Low | ^ | ^ | 0x212D | no |
| ^ | High |  2  | ^ | 0x2236 | no |
| ^ | Medium | ^ | ^ | 0x2220 | no |
| ^ | Low | ^ | ^ | 0x222B | no |
| ^ | High |  4  | ^ | 0x2334 | no |
| ^ | Medium | ^ | ^ | 0x2322 | no |
| ^ | Low | ^ | ^ | 0x2329 | no |
| ^ | High |  10  | ^ | 0x2737 | no |
| ^ | Medium | ^ | ^ | 0x2722 | no |
| ^ | Low | ^ | ^ | 0x272A | no |
| Read serial number | | | | 0x3780 | no |
| Fetch Data | | | | 0xE000 | no |
| Accelerated Response Time | ^ | ^ | ^ | 0x2B32 | no |
| Break continuous acquisition | ^ | ^ | ^ | 0x3093 | no |
| Soft Reset | ^ | ^ | ^ | 0x30A2 | yes |
| Heater enable | ^ | ^ | ^ | 0x306D | yes |
| Heater disable | ^ | ^ | ^ | 0x3066 | yes |
| Read out status register | ^ | ^ | ^ | 0xF32D | yes |
| Clear status register | ^ | ^ | ^ | 0x3041 | yes |
| Read high alert limit | set | ^ | ^ | 0xE11F | no |
| ^ | clear | ^ | ^ | 0xE114 | no |
| Read low alert limit | set | ^ | ^ | 0xE109 | no |
| ^ | clear | ^ | ^ | 0xE102 | no |
| Write high alert limit | set | ^ | ^ | 0x611D | no |
| ^ | clear | ^ | ^ | 0x6116 | no |
| Write low alert limit | set | ^ | ^ | 0x610B | no |
| ^ | clear | ^ | ^ | 0x6100 | no |

---++ The SHT30 command codes

The SHt30 uses 16 bit command codes with a 3-bit CRC (cyclic redundancy check) calculated over the upper 13 bit added on the lowest significant 3 bits.<br />Let us have a look at the "one time measurement" commands in order to understand the command layout. Here is the table from the data sheet:

<img alt="sht30commandCode.png" height="267" src="%ATTACHURL%/sht30commandCode.png" title="sht30commandCode.png" width="446" />

If we analyze the codes we get:

| Repeatability | Clock Stretching | Command code | bit for clock stretching | rest of command code | bits for repeatability | CRC |
| High | enabled | 0010 | 1 | 100 | 0000 0 | 110 |
| Medium | ^ | 0010 | 1 | 100 | 0000 1 | 101 |
| Low | ^ | 0010 | 1 | 100 | 0001 0 | 000 |
| High | disabled | 0010 | 0 | 100 | 0000 0 | 000 |
| Medium | ^ | 0010 | 0 | 100 | 0000 1 | 011 |
| Low | ^ | 0010 | 0 | 100 | 0001 0 | 110 |
As you can see, knowing the repeatability and the clock stretching parameter we can easily construct the command code: Starting from a command code 0x2400 we set bit 11 if clock stretching is enabled and we "or" 01 into bits 3 and 4 for medium and 10 for low repeatability to get the command code. This code we use as a key into a dictionary from where we can pick up the 3 bit checksum, which we or to bits 0..2 .
---++ Methods available in the !SHT3X class

Here is a list of the available methods of the !SHT3Xclass:

*__init__(scl_pin=machine.Pin(22),sda_pin=machine.Pin(21),i2c,address=0x45)*: creates an instance of the !SHT3X object. The default values for scl_pin, sda_pin and i2c_address should be ok for the ESP32 and our version of the SHT30 shield. The method raises an !SHT3XError.BUS_ERROR if the sht30 chip is not found on the !I2C bus

_from sht3x import !SHT3X_

_sht30 = !SHT3X()_

should therefore work and create the !SHT3X object.

*sht30.isPresent()*: returns <i>True </i>if the sht30 is chip is found on the !I2C bus, _False_ otherwise

<b>sht30.serialNumber(): </b>Returns the 32 bit serial number of the sht30 chip

<b>sht30.readStatus(): </b>Returns the status bits (16 bits) from the status register

<b>sht30.printStatus(): </b>Prints the status bits from the sht30 status register in a humanly readable form

*sht30.clearStatus()*: Clears the status register

*sht30.softReset()*: Resets the sht30

*sht30.enableHeater()*: Switches the heater on

*sht30.disableHeater()*: Switches the heater off

*sht30.getTempAndHumi(clockStretching=!SHT3X.CLOCK_STRETCH, repeatability=!SHT3X.REP_S_LOW, raw=False, timeout=100)*

gets temperature and humidity in the selected mode. If clock stretching as been selected the corresponding command 0x2cxx is issued followed by a wait until the measurement has been completed. The wait time used is the maximum measurement time for that mode found in table 4 chapter 2.2 of the data sheet.

If no clock stretching is selected, the method will poll the sht30 every ms for the result data. If within "timeout ms" the sht30 does not return the result an !SHT3X.TIMEOUT error is raised.

After the wait, the data are read out and the checksum checked. If the checksum received is wrong an !SHT3X.CRC_ERROR is raised.

If raw mode has been selected, the 6 byte result (16 bits for temperature, 16 bits humidity and 2*8 bits checksums) is returned. Otherwise the raw values are converted to physical temperature values (in °C) and relative humidity (in %) which are returned to the caller.

*sht30.Celsius2Fahrenheit(tempC)*: takes a temperature value in °C and converts it to °F

<b>sht30.startPeriodicMeas(mps=0.5,repeatability=self.REP_P_HIGH): </b>starts repetitive measurements in the selected mode. In "continuous mode" clock stretching is not done. Here I wait for the period selected before the data are read out.

*sht30.stopPeriodicMeas()*: Stops "continuous measurement mode"

<b>sht30.measPeriodic(self,mps=0.5, repeatability=REP_P_HIGH, raw=False, noOfMeas=50, callback=None): </b>Starts continuous measurements using sht30.startPeriodicMeas(), reads out the data after each measurement and stops continuous measurements using stopPeriodicMeas() as soon as "noOfMeas" measurements have been reached. You can specify a callback function which is called with [tempC,humi], the temperature in °C and the humidity value in % as parameter if raw is False or with the raw data [tempRaw,humiRaw,checksum] as parameter if raw is True.

<b>sht30.readAlert(high=True,set=True,raw=False): </b>Reads the alert limits. Returns temperature and humidity limits for alerts in °C and % or the raw data read out if raw == True.

<b>sht30.writeAlert(self,tempC,humi,high=True,set=True): </b>Write the alert limits

Here you find the driver itself:

%ATTACHURL%/sht3x.py.txt

and here some test code exercising the driver:

%ATTACHURL%/sht3xTest.py.txt

And here is the result printed out by the test program:

&gt;&gt;&gt; %Run -c $EDITOR_CONTENT<br />Serial number: 0x317d411<br />Measure with clock stretching, the delay between writing the cmd and reading back the result<br />is calculated from the repeatabilty parameter (see data sheet)<br />Temperature: 24.26994 °C, Humidity: 61.74011 %<br />Measure without clock stretching<br />After sending the command the SHT30 is polled for the result every 1ms<br />Generates a timeout exception if the SHT30 does not respond in time<br />Temperature: 24.28329 °C, Humidity: 61.75385 %<br />Read and print the alert settings: High limit to set the alert<br />The data sheet says that this should be 60°C and 80%<br />Temperature limit high: 59.93164 °C Humidity limit high: 79.6875 %<br />Set accelerated response time<br />Print the current status register contents<br />--------------------------------------------------<br />Status register content: 0x2060<br />--------------------------------------------------<br />No alert pending<br />Heater is enabled<br />Last command succeeded<br />Checksum of last write command was correct<br />Clear the status register, switch on the heater and print the values again<br />Switch on the heater<br />--------------------------------------------------<br />Status register content: 0x20a0<br />--------------------------------------------------<br />No alert pending<br />Heater is enabled<br />Last command succeeded<br />Checksum of last write command was correct<br />Start periodic measurement<br />We pass the function printContinuousValues as callback routine, printing the temperature and humidity values<br />read out in each measurement cycle<br />Period measurement will take 20.0 s<br />Interval: 2.0<br />Temperature: 24.21387 °C, Humidity: 61.6684 %<br />Temperature: 24.26994 °C, Humidity: 61.78131 %<br />Temperature: 24.28329 °C, Humidity: 61.79504 %<br />Temperature: 24.24057 °C, Humidity: 61.80878 %<br />Temperature: 24.25392 °C, Humidity: 61.83167 %<br />Temperature: 24.24057 °C, Humidity: 61.82861 %<br />Temperature: 24.22722 °C, Humidity: 61.85608 %<br />Temperature: 24.24057 °C, Humidity: 61.91101 %<br />Temperature: 24.22722 °C, Humidity: 61.92932 %<br />Temperature: 24.21387 °C, Humidity: 61.90643 %<br />--------------------------------------------------<br />Status register content: 0x2000<br />--------------------------------------------------<br />No alert pending<br />Heater is enabled<br />Last command succeeded<br />Checksum of last write command was correct<br />&gt;&gt;&gt;

-- %USERSIG{UliRaich - 2020-05-22}%

---++ Comments

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I	Attachment	History	Action	Size	Date	Who
png	sht30commandCode.png	r1	manage	24.8 K	2020-05-24 - 18:11	UliRaich
txt	sht3x.py.txt	r1	manage	18.5 K	2020-05-23 - 19:48	UliRaich
txt	sht3xTest.py.txt	r1	manage	2.7 K	2020-05-23 - 19:48	UliRaich
This topic: IoT_Course_English > WebHome > SHT30NopI2CTemperatureAndHumiditySensor
Topic revision: r7 - 2022-06-16 - UliRaich