Project Files of SHT31 Sensor Library for Proteus V1.1 (Temperature + Humidity Sensor + Arduino)

SHT31 TEMPERATURE HUMIDITY SENSOR (GY-SHT31-D) LIBRARY FOR PROTEUS - V1.1
Designed by The Engineering Projects
www.TheEngineeringProjects.com

IMPORTANT LINKS
Article (read it first - pictures, step by step, every feature explained):
  https://www.theengineeringprojects.com/2026/09/sht31-proteus-library.html
Report a bug or suggest a feature (our forum):
  https://www.theengineeringprojects.com/forum/category/sht31-proteus-library
The demo uses our TEP Serial Monitor Advance (included) instead of Proteus's
Virtual Terminal - its own article:
  https://www.theengineeringprojects.com/2026/10/serial-monitor-advance-proteus-library.html
Support us (the libraries are free):
  https://www.theengineeringprojects.com/donate

FILE STRUCTURE
SHT31-TEP-v1.1/
|-- Proteus Library Files/
|   |-- ArduinoV3TEP.IDX                          0.8 KB   its index -> LIBRARY folder
|   |-- ArduinoV3TEP.LIB                         95.6 KB   TEP Arduino UNO (demo) -> LIBRARY folder
|   |-- TEPSERIALMON.LIB                         11.1 KB   TEP Serial Monitor Advance -> LIBRARY folder
|   |-- TEPSHT31.LIB                             44.4 KB   SHT31 Simple + Advance (2 devices) -> LIBRARY
|-- Proteus Model Files/
|   |-- TEPSERIALMON.DLL                        978.0 KB   Serial Monitor model -> MODELS folder
|   |-- TEPSHT31.DLL                            537.0 KB   the TEP I2C sensor model -> MODELS
|-- Proteus Simulation/
|   |-- SHT31_Demo.hex                           38.4 KB   both UNOs (the demo sketch v1.1)
|   |-- SHT31-ArduinoUnoV3.pdsprj                22.9 KB   demo: UNO 1 + SHT31 Simple, UNO 2 + Advance
|   |-- TEPSERIALMON.DLL                        978.0 KB   copy of the monitor model
|   |-- TEPSHT31.DLL                            537.0 KB   copy of the model so the demo runs as is
|-- Arduino Code/
|   |-- SHT31_Demo/SHT31_Demo.ino                 6.4 KB   sketch (source of the .hex)
|   |-- libraries/Adafruit_SHT31/                13.3 KB   Adafruit SHT31 2.2.2, BSD, 6 files
|   |-- libraries/Adafruit_BusIO/                77.0 KB   Adafruit BusIO 1.17.4, MIT, 24 files
|-- README.txt                                  ~27.7 KB   this file
Total: 3.29 MB (unzipped). The C++ source code of the model is not included.

WHAT IS IT?
A simulation model of the Sensirion SHT31 (SHT3x-DIS) temperature and humidity
sensor on the common purple GY-SHT31-D breakout, for Proteus 8. Your Arduino
talks to it over I2C exactly as to the real chip (address 0x44 with ADDR low,
0x45 with ADDR high) and the popular Adafruit SHT31 library runs unmodified:
begin, readTemperature, readHumidity, readBoth, readStatus, heater /
isHeaterEnabled, reset. The model speaks the SHT31's command protocol: single
shot measurements with their real duration (a read before the result is ready
is NACKed), periodic mode (0.5 .. 10 measurements / s, Fetch Data, Break), ART,
the CRC-8 on every word, the status word, the heater, the serial number - and
v1.1 adds the sensor's alert mode with the ALERT pin, a heater that really
warms the sensor (it reads a higher temperature and a lower humidity, the dew
point stays) and, if you want it, the real response time of the sensor (2 s for
temperature, 8 s for humidity). You set the temperature and the humidity with
sliders, presets (ROOM, SHOWER, FRIDGE, DESERT, BREATH, REAL TAU) or by
clicking the thermometer or the water drop above the board.
The part looks like the GY-SHT31-D: the purple board, the mounting hole, the
white SHT31 with its dark sensing opening, the small parts and the board print.
Above the board sits an animated climate view: a thermometer, a water drop that
fills with the humidity, the dew point, the heater (with how much it warms the
sensor) and an ALERT sign. On the board: a red PWR LED, a blue I2C LED that
flashes for every I2C transaction to this sensor and an amber ALERT LED that
lights while the ALERT pin is high - TEP additions (the real board has no LED) -
and the live I2C address (0x44 / 0x45).

TWO DEVICES IN ONE LIBRARY (search "SHT31" in Pick Devices):
  SHT31 Simple      device SHT31TEP       "SHT31 Temperature Humidity Sensor - Simple"
                    On-Sheet Panel: a control panel on the schematic next to the
                    board - six presets, the two sliders of v1.0 (drag them:
                    TEMPERATURE, HUMIDITY) and what your sketch READ over I2C
                    (decoded by the model as the Adafruit library converts it,
                    the dew point as the demo computes it: "SKETCH READ: 24.99 C
                    50.00 % DEW POINT 13.8 C"), the set values and what the sensor element
                    sees (the heater included). The red X in the panel's header
                    closes it, the PANEL button on the board opens it again. Your
                    v1.0 designs keep working with this device.
  SHT31 Advance     device SHT31ADVTEP    "SHT31 Temperature Humidity Sensor - Advance"
                    Pop-Up Panel: only the board on the schematic; at Run a TEP
                    pop-up window opens - the same look as the TEP Serial Monitor
                    (move it by its header, resize it, minimise it). The tabs
                    Sensor and Test sit in the header; the gear and ? icons open
                    Settings and Help; the palette icon switches the theme:
                      Sensor    the live climate view (click the thermometer or
                                the drop), the presets, a click-slider with - / +
                                for every input, the last reading as big tiles, and
                                what the Arduino read over I2C (the values, the dew
                                point, the sensor element, the status word, the I2C
                                address and the measured SCL clock)
                      Test      four tools measured on the model with your sketch:
                                I2C check, Timing, Step response, Dew point &
                                heater (see THE TEST TOOLS below)
                      Settings  theme (TEP Dark / Light), text size, open at Run,
                                window size - remembered for your Windows user
                      Help      Help & Support like the TEP Serial Monitor: report a
                                bug, suggest a feature, article, user guide,
                                updates, donate, website, forum; Copy diagnostics
                                (the inputs, what was read, the registers, the last
                                transactions, the test results) for a bug report
                    The OPEN PANEL button on the board opens the window again
                    after you close it.
Both devices use the same model (TEPSHT31.DLL) and the same properties.

NEW IN V1.1
* Two devices: SHT31 Simple (panel on the sheet, close / open) and SHT31
  Advance (pop-up window with the live climate view, four test tools, settings
  and help) - see above.
* Board: the real GY-SHT31-D's look (purple, the mounting hole, the white SHT31
  with its opening) with an animated climate view above it (thermometer, water
  drop, dew point, heater, alert), PWR / I2C / ALERT LEDs (a TEP addition), the
  live I2C address, a PANEL / OPEN PANEL button and a SIMPLE / ADVANCE badge.
* Model - the ALERT pin and the alert mode (a known gap of v1.0): the four alert
  limits (read E11F / E114 / E109 / E102, write 611D / 6116 / 610B / 6100 with a
  CRC - a bad CRC is ignored and sets status bit 0), the datasheet defaults (80 %
  / 60 C set, 79 % / 58 C clear, 22 % / -9 C clear, 20 % / -10 C set), checked
  after every periodic measurement with the set / clear hysteresis; status bits
  15 / 11 / 10 and the ALERT pin (active high) follow.
* Model - the heater warms the sensor (+4 C with a 4 s time constant): the
  temperature it reports rises, the humidity falls and the dew point stays -
  as on the real sensor (v1.0: only the status bit).
* Model - the real response time on request (the REAL TAU preset / the RESPONSE
  property): tau63 2 s for the temperature, 8 s for the humidity; status 0x8010
  after a reset (the datasheet value); ART (4 measurements / s).
* Model - the command protocol decoded in an I2C transaction log ("write 2400
  (single shot, high repeatability)", "read -> 25.00 C, 50.00 % (CRC OK)", the
  busy NACKs) and the measured SCL clock.
* The demo: ONE project with two UNOs - UNO 1 with SHT31 Simple, UNO 2 with
  SHT31 Advance - each with the TEP Serial Monitor Advance instead of the
  Virtual Terminal (U3 = UNO 1, U4 = UNO 2, quick buttons) and an LED on A0.
* The demo sketch (v1.1) keeps every v1.0 line and adds: the dew point line, a
  humidity alarm on the LED (above 70 %), and the Serial Monitor commands HELP,
  STATUS, HEATER ON / OFF, ALERT ON / OFF (the sensor's own alert mode, set up
  with raw commands), HUMID. It prints nothing periodically except the readings.
* Version 1.1 everywhere; the C++ source code is no longer included (and
  neither is the Arduino AVR core archive - its GitHub link is below).

TEST STATUS
v1.1: verified in Proteus 8.5 on 8 Oct 2026 (the demo run from this package's
Proteus Simulation folder):
  * start-up: "Temperature: 25.0 C | Humidity: 50.0 %", "Dew point: 13.8 C";
  * ALERT ON 60 + SHOWER (with the real response): at 62.8 % "SHT31 alert:
    humidity above the limit (ALERT pin high)", at 71.2 % "Humidity alarm: above
    the limit (LED on)";
  * the four tools on U2: I2C check (0x44, status 8010, 0 NACKs, SCL 91 kHz, CRC
    OK reads in 691 us); Timing (6 measurements of 15.50 ms every 522.63 ms, 6
    reads, data age 5.3 ms); Step response "Humidity, real tau" 50 -> 80 -> 50 %
    (first reading 949.4 / 324.7 ms, 90 % after 18756.7 / 18110.2 ms, 38 readings
    each); Dew point & heater after HEATER ON on U4 (room 13.9, bathroom 26.2,
    fridge 1.7, desert 8.5 C, all +0.00 C, "heater on: +2.6 / +3.6 / +3.9 / +4.0 C");
  * a v1.0 design (the v1.0 release demo with this DLL): the v1.0 panel,
    "Temperature: 25.0 C | Humidity: 50...".
After that run (PC-tested, to be re-checked in Proteus): the panel's dew point uses
the demo's conversion and formula (13.8 C, as the demo prints), the Timing tool
states the datasheet's typical / max times correctly, every register has its own
row (no cut text), the Test pages fill the window. The re-check in Proteus
(8 Oct) passed all of that and found two more, fixed afterwards (PC-tested, to be
re-checked in Proteus): the "Humidity, real tau" steps now hold 48 s (6 tau) so
each settles (2 %) inside its step, and step 1 waits until the readings sit at
the start value; while SHOWER or BREATH runs, the humidity / temperature sliders
stay at the value you set, labelled "(base)", and say what the sensor gets now
("SHOWER now 95.0 %") - on the sheet panel and in the pop-up.
PC tests (8 Oct 2026, this package's DLL / LIB / sketch):
  2817 automatic checks on a PC, 0 failed, plus the v1.0 test, unchanged and
  passing with the v1.1 model (SHT31: official Adafruit CRC checks, 12
  environments, heater status, alternate address and busy NACK); 13 chip checks
  for v1.1 (the busy NACK, the heater (a warmer sensor, the same dew point),
  alert limits with CRC, the ALERT pin with hysteresis, periodic and ART rates,
  the real response time); 72 on the complete Proteus model (the LIB (pins,
  properties, both devices), power, ADDR, the PWR / I2C / ALERT LEDs, the panel,
  red X / PANEL, OPEN PANEL, the pop-up pages and links, the command protocol
  decoded, busy NACKs, the heater, the alert mode and a bad CRC, the real
  response, the presets and effects (SHOWER / BREATH: the sliders keep the base
  and say what the sensor gets now), the scene click, the four tools, a design
  with the v1.0 symbol); 30 with the real v1.1 demo sketch and the unmodified
  driver library on two UNOs (every v1.0 output line, the dew point line and
  humidity LED, every Serial Monitor command incl. the alert mode, SHOWER on the
  panel (base + now = what the sketch prints), the Timing / Step response (the
  real response x3 right after a SHOWER: it waits for the start value, settles
  inside each 48 s step) / Dew point & heater tools with the real sketch); 2702
  on the rendered boards and pop-up windows (every page fits in TEP Dark and
  Light, at Large text and 150 % DPI; every tool's hint lines and every header
  state fit).
v1.0 (29 Sep 2026): the v1.0 demo was opened, run and checked in Proteus 8.5
  (25.0 C / 50.0 % at the start, 60.0 C / 50.0 % after the temperature drag,
  60.0 C / 78.4 % after the humidity drag, no CRC errors); the v1.0 tests (the
  unmodified Adafruit library over the bit-level I2C slave: CRC checks, 12
  environments, heater status, alternate address, busy NACK) still pass with
  the v1.1 model.

INSTALLATION (about 2 minutes)
1. Close Proteus. Extract the WHOLE ZIP to a normal folder (e.g. Desktop).
2. Copy everything in "Proteus Library Files" (TEPSHT31.LIB with both devices,
   TEPSERIALMON.LIB and the TEP Arduino UNO V3 library ArduinoV3TEP.LIB / .IDX
   used by the demo) to the LIBRARY folder of Proteus, for example:
     C:\Program Files (x86)\Labcenter Electronics\Proteus 8 Professional\LIBRARY
   (on some PCs: C:\ProgramData\Labcenter Electronics\Proteus 8 Professional\
   LIBRARY - use the folder that already holds Proteus's own .LIB files).
3. Copy TEPSHT31.DLL and TEPSERIALMON.DLL from "Proteus Model Files" to the
   MODELS folder (...\Proteus 8 Professional\MODELS).
4. Updating from v1.0: replace TEPSHT31.LIB and TEPSHT31.DLL, and
   delete TEPSHT31.IDX if there is one in the LIBRARY folder. A v1.0 design keeps
   its v1.0 symbol: it runs with the new model and shows the v1.0 panel (without
   the v1.1 board parts and the red X) - re-pick the part to get the v1.1 symbol.
5. Start Proteus. In Pick Devices (P) search "SHT31": you get the Simple and the
   Advance device (category Sensors > Environmental, as in v1.0).
The model DLL is the TEP I2C sensor family model: TEPMPU6050.DLL, TEPBMP280.DLL,
TEPMAX30102.DLL, TEPVL53L0X.DLL, TEPSHT31.DLL and TEPTCS34725.DLL are identical
files under the v1.0 names, so every v1.0 design finds its model.

RUN THE DEMO
"Proteus Simulation\SHT31-ArduinoUnoV3.pdsprj" - keep SHT31_Demo.hex and the
two DLLs beside the project.
  UNO 1 (ARD1): SHT31 Simple (U1), Serial Monitor U3.
  UNO 2 (ARD2): SHT31 Advance (U2), Serial Monitor U4.
  Both UNOs run SHT31_Demo.hex. An LED (D1 / D2) with 220 ohm on A0 of each
  UNO: the humidity alarm.
  1. Press Run. Both monitor windows open (9600 baud) and so does U2's pop-up.
     U3 and U4 show "TEP SHT31 - drag the temperature and humidity sliders." and
     "TEP SHT31 Demo v1.1 - type HELP in the Serial Monitor", then twice a
     second:
       Temperature: 25.0 C | Humidity: 50.0 %
       Dew point: 13.8 C
     (the exact dew point of 25 C / 50 % is 13.85 C.) The blue I2C LED on each
     board flashes with every measurement.
  2. U1: drag HUMIDITY above 70 % - "Humidity alarm: above the limit (LED on)",
     LED D1 lights. SHOWER: the humidity climbs to 95 % in 8 s and falls again
     (the slider keeps your 50.0 % "(base)"; under it "SHOWER now 95.0 %");
     BREATH: a quick breath on the sensor; FRIDGE / DESERT; REAL TAU: now the
     readings follow a slider change slowly, like a real SHT31 (humidity 8 s).
     Close the panel with its red X and open it with PANEL.
  3. U3 / U4 quick buttons: STATUS ("Status: 0x8010 - heater OFF, alert pending
     ..."), HEATER ON (in a few seconds the temperature reads about 4 C more,
     the humidity less, the dew point stays), HEATER OFF, HELP. Type ALERT ON 60
     and drag the humidity above 60 %: "SHT31 alert: humidity above the limit
     (ALERT pin high)" and the amber ALERT LED on the board; ALERT OFF.
  4. U2 (Advance): the Sensor page shows the same inputs and what the sketch
     read; the Test page has the four tools (below).
  5. Close U2's window and open it again with OPEN PANEL on the board.
Closed a monitor window? Click OPEN MONITOR on the monitor part.

WIRING (as in the v1.0 demo)
VIN -> supply, GND -> GND, SCL -> A5, SDA -> A4, ADDR -> GND (address 0x44; ADDR
high = 0x45); ALERT not connected (it is optional: it drives the ALERT LED and
can go to D2 for attachInterrupt).
In the sketch: Adafruit_SHT31 sensor;  sensor.begin(0x44);  Serial 9600.
Serial Monitor RXD <- Arduino D1 (TX), Serial Monitor TXD -> Arduino D0 (RX),
Serial Monitor GND -> ground. RXD2 is not needed: I2C has no serial line to
watch. The humidity LED + 220 ohm from A0 to GND.
Pin order in Proteus: VIN GND SCL SDA ADDR ALERT (v1.0; the GY-SHT31-D has VIN
GND SCL SDA in a row and AD / AL as separate pads).
REAL HARDWARE:
 * Supply: the GY-SHT31-D has no regulator - VIN goes straight to the sensor,
   which runs on 2.4 .. 5.5 V; 3.3 V is the usual choice (5 V works).
 * I2C pull-ups: 10 k on the board (to VIN), so A4 / A5 need nothing else.
 * Address: ADDR low = 0x44, high = 0x45 - two SHT31 on one bus.
 * ALERT is active high (push-pull), only in periodic mode.
 * Self-heating: keep the sensor away from the regulator and the MCU; the
   heater is for removing condensation and for a plausibility check, not for
   normal measuring. Accuracy of the real SHT31: +-2 % RH, +-0.3 C; the model
   gives exact values.

THE TEST TOOLS (SHT31 Advance, Test tab) - what they really measure
Every tool runs on the live model with your sketch: it changes the sensor's
inputs (and restores them) and watches the I2C traffic your Arduino really
makes - it never talks to your Arduino. Each tool shows one "Good for:" line and
one line on how it measures.
  I2C check       Good for: checking that the SHT31 answers and what your
                  sketch really told it. The sensor's state decoded (the
                  address and the ADDR level, the status word - marked when a
                  command or a CRC failed -, the last command, single shot /
                  periodic, the four alert limits as % RH / C, the ALERT pin, the
                  heater and how much it warms the sensor now, the busy NACKs,
                  the limit CRC errors), transactions, bytes, NACKs, the
                  measured SCL clock and the last transactions decoded (repeats
                  folded). With the demo: "write 2400 (single shot, high
                  repeatability)", "read -> 25.00 C, 50.00 % (CRC OK)".
  Timing          Good for: seeing how long a measurement takes and whether
                  your sketch reads it in time. Records for 1, 3 or 10 s every
                  measurement and every read: the measurement time, the period
                  (periodic mode), the sketch's read period, the data age at
                  each read and the busy NACKs (a read before the result is
                  ready), with the datasheet times. With the demo: a 15.5 ms
                  measurement per reading, read about 5 ms after it ended
                  (Adafruit waits 20 ms), a reading every 520 ms, no busy NACK.
  Step response   Good for: seeing how quickly a change reaches your sketch -
                  measurement, read period and, with the real response time, the
                  sensor itself. Steps the temperature (25 -> 35 C), the
                  humidity (50 -> 80 %) or the humidity with the real response
                  time (tau 8 s, 48 s = 6 tau per step) 1, 3 or 5 times and
                  plots every reading; per step: the first reading that shows it
                  (10 %), 90 % and settled (2 %). Step 1 waits until the
                  readings sit at the start value (e.g. the sensor still drying
                  after a SHOWER: "Settling at 50.0 % (the sketch reads 63.2 %)"),
                  so the chart starts flat. With the demo: the next reading
                  (within 520 ms); with the real response: 90 % after about
                  18.5 s, settled (2 %) after about 31.5 s.
  Dew point &     Good for: checking your dew point maths in four climates -
  heater          and seeing what the heater does to the readings. Holds room
                  25 C / 50 %, bathroom 28 / 90, fridge 4 / 85, desert 40 / 15
                  (5 s each) and computes the dew point (Magnus, Sensirion's
                  constants 243.12 / 17.62) from what your sketch read; the last
                  point (8 s) checks the heater: type HEATER ON first - the
                  sensor reads about +4 C and the dew point stays. With the demo:
                  4 / 4 within 0.3 C, then "OK: +4.0 C, dew point kept".

THE DEMO SKETCH ON THE SERIAL MONITOR (SHT31_Demo v1.1)
  HELP                    the command list
  STATUS                  the sensor's status word decoded (heater, alert, mode)
  HEATER ON | OFF         the sensor's heater
  ALERT ON [rh] | OFF     the sensor's own alert: writes the high limits (rh,
                          default 70 %; clear 2 % lower) and starts periodic mode
                          (4 / s, read with Fetch Data); prints when the alert
                          sets or clears
  HUMID rh                the LED's humidity alarm level (default 70 %)
Monitor quick buttons in the demo: STATUS, HEATER ON, HEATER OFF, HELP.
Every line the sketch prints has at most 80 characters (it fits the Serial Monitor's
Simple interface); longer answers are split, the second line indented.

EXPECTED MONITOR OUTPUT (U3 and U4)
  TEP SHT31 - drag the temperature and humidity sliders.
  TEP SHT31 Demo v1.1 - type HELP in the Serial Monitor
  Temperature: 25.0 C | Humidity: 50.0 %
  Dew point: 13.8 C
After dragging to 60 C / 78.4 % (as in the v1.0 check):
  Temperature: 60.0 C | Humidity: 78.4 %
  Dew point: 54.9 C
  Humidity alarm: above the limit (LED on)
After STATUS:
  Status: 0x8010 - heater OFF, alert pending, single shot, LED above 70 %

PROPERTIES (double-click the sensor > Edit Properties; the same on Simple and
Advance - the v1.0 properties and one new)
  TEMPERATURE     temperature in C, -40 .. 125 (default 25)
  HUMIDITY        relative humidity in %, 0 .. 100 (default 50)
  RESPONSE        v1.1: 1 = the real response time (tau 2 s / 8 s), 0 = at once
                  as v1.0 (default 0; the REAL TAU preset)
The panel style is chosen by the device (Simple / Advance), not by a property.
The Advance window settings (theme, text size, open at Run, size) are on its
Settings page. The demo's Serial Monitors: BAUD 9600, THEME TEPDARK, AUTOOPEN
YES, QUICK1-4 as above (see the Serial Monitor's article for all its
properties).

LINKS.INI (OPTIONAL)
The Help page cards of the Advance device open web pages. To point them
somewhere else without a new DLL, put a text file named links.ini next to
TEPSHT31.DLL with lines KEY=URL, for example:
  ARTICLE=https://www.theengineeringprojects.com/...
Keys: WEBSITE, FORUM, BUG_REPORT, FEATURE_REQUEST, ARTICLE, USER_GUIDE,
UPDATE_CHECK, DONATE. Only http:// and https:// links are used; lines starting
with # are comments.

TROUBLESHOOTING
* "SHT31 not found. Check power, SDA, SCL and ADDR.": check VIN / GND (the PWR
  LED must be lit and the board shows "I2C 0x44"), SDA -> A4, SCL -> A5, and
  that ADDR matches the address in begin() (0x44 = ADDR low).
* "Measurement or CRC error.": the sensor did not answer (power, wiring) or a
  CRC did not match; in your own sketch also: reading a single shot before it
  is ready (15 ms at high repeatability) - the sensor NACKs, the I2C check
  counts busy NACKs.
* The values change slowly: the REAL TAU preset / RESPONSE = 1 is on.
* The temperature is a few degrees too high: the heater is on (STATUS, the
  board's view shows HEATER +x C) - HEATER OFF.
* ALERT never fires: the SHT31 checks its limits only in periodic mode (ALERT
  ON in the demo); with single shot measurements the ALERT pin stays low.
* The part is not simulated / no panel: TEPSHT31.DLL is missing from MODELS and
  from the project folder. No monitor window: TEPSERIALMON.DLL is missing, or
  click OPEN MONITOR on the monitor part.
* Advance: the pop-up does not appear - click OPEN PANEL on the board, use
  Proteus's Debug menu, or turn "Open the panel at Run" on its Settings page
  back on.
* Simple: the red X does not close the panel /
…