Project Files of PC817 Optocoupler Library for Proteus: PC817 and 4N35

PC817 OPTOCOUPLER LIBRARY FOR PROTEUS - V1.0 (PC817 and 4N35 optocouplers with a pop-up)
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/2026/11/pc817-optocoupler-library-for-proteus.html
Report a bug or suggest a feature (our forum):
  https://www.theengineeringprojects.com/forum/category/pc817-optocoupler-proteus-library
The demo runs on our Arduino UNO V4.0 (included) - working LEDs, RESET and a
built-in serial monitor, no Virtual Terminal to wire - its own article:
  https://www.theengineeringprojects.com/2026/10/arduino-uno-library-for-proteus-v40.html
The 24 V switch is our own push button (included):
  https://www.theengineeringprojects.com/2026/11/push-button-library-for-proteus.html
the 12 V lamp is our own 5 mm LED (included):
  https://www.theengineeringprojects.com/2026/11/5mm-led-library-for-proteus.html
Support us (the libraries are free):
  https://www.theengineeringprojects.com/donate

FILE STRUCTURE
PC817-Optocoupler-TEP-v1.0/
|-- Proteus Library Files/
|   |-- ArduinoV4TEP.LIB                              201.9 KB   TEP Arduino boards V4.0 (UNO) -> LIBRARY
|   |-- TEPBUTTON.LIB                                  20.7 KB   a part the demo uses -> LIBRARY folder
|   |-- TEPLED5MM.LIB                                  21.8 KB   a part the demo uses -> LIBRARY folder
|   |-- TEPOPTO.LIB                                    30.0 KB   the library -> LIBRARY folder
|   |-- TEPRESISTOR.LIB                               306.9 KB   a part the demo uses -> LIBRARY folder
|-- Proteus Model Files/
|   |-- TEPARDUINO.DLL                                883.5 KB   the Arduino board model -> MODELS folder
|   |-- TEPBUTTON.DLL                                 274.0 KB   its model -> MODELS folder
|   |-- TEPLED5MM.DLL                                 289.5 KB   its model -> MODELS folder
|   |-- TEPOPTO.DLL                                   306.0 KB   the model -> MODELS folder
|   |-- TEPRESISTOR.DLL                               311.0 KB   its model -> MODELS folder
|-- Proteus Simulation/
|   |-- Opto_Demo.hex                                  12.1 KB   the demo firmware
|   |-- Optocoupler-Isolation-ArduinoUnoV4.pdsprj      24.9 KB   the demo project
|   |-- TEPARDUINO.DLL                                883.5 KB   copy of the board model
|   |-- TEPBUTTON.DLL                                 274.0 KB   copy of its model
|   |-- TEPLED5MM.DLL                                 289.5 KB   copy of its model
|   |-- TEPOPTO.DLL                                   306.0 KB   copy of the model
|   |-- TEPRESISTOR.DLL                               311.0 KB   copy of its model
|-- Arduino Code/
|   |-- Opto_Demo/Opto_Demo.ino                         3.3 KB   the demo sketch (source of the .hex)
|-- README.txt                                        ~14.8 KB   this file
Total: 4.65 MB (unzipped). The C++ source code of the models is not included.

WHAT IS IT?
Two optocouplers, drawn at true scale (the top view): an infrared LED and a phototransistor with
nothing between them but light.
  * PC817 - DIP-4 (1 A, 2 K, 3 E, 4 C), 4.58 x 6.5 mm: CTR 50 to 600 % at 5 mA, sold in ranks A
    (80-160 %), B (130-260 %), C (200-400 %)
    and D (300-600 %); 80 V, 50 mA; 5000 Vrms between its two sides. The rank is printed on the
    body: pick it in Edit Properties.
  * 4N35 - DIP-6 (1 A, 2 K, 3 not connected, 4 E, 5 C, 6 B): CTR 100 % or more at 10 mA; its base on
    a pin; 70 V, 50 mA, 5000 Vrms.
  * One analog model: the LED (VF from the datasheet, burns out past its rating), the light as a
    photocurrent into the base, and the
    phototransistor (a Gummel-Poon-style law with a recombination current, so CTR rises, peaks and
    falls with IF as on the datasheet curve),
    with the charges of its junctions - so the switching times follow the load resistor and a base
    resistor, as on a real part.
  * It says whether its output is OFF, ON (CTR now) or SWITCHED ON (the load sets the current),
    recognises PWM on the LED, and measures its own
    turn-on and turn-off delays. Click one at Run for the pop-up: inside the package, CTR against IF
    with the rank's band, graphs,
    an event log and a check page.
The body is drawn as on the real part and to true scale against our Arduino.
The TEP signature and the pop-up are TEP additions.

TWO DEVICES (search "PC817" or "4N35" in Pick Devices):
  PC817TEP     "PC817 Optocoupler V1.0" in TEPOPTO.LIB (Optoelectronics > Optocouplers), prefix U,
  model TEPOPTO.DLL. Pins 1 A, 2 K, 3 E, 4 C.
  OPTO4N35TEP  "4N35 Optocoupler V1.0" in TEPOPTO.LIB, prefix U, model TEPOPTO.DLL. Pins 1 A, 2 K, 4
  E, 5 C, 6 B (pin 3 is not connected).

THE POP-UP
Click the part at Run. Tabs:
    Optocoupler  inside the package (the LED's glow and the light across the gap, the pins lit while
    their current flows, the voltage across
                 the gap), CTR against IF on a log scale with the rank's band and the working point,
                 and eight live values: IF, VF, IC, VCE,
                 CTR now, the delays on and off, the power and the gap. While the LED is pulsed the
                 values are averages.
                 The toolbar: New part, the pins, the rank.
    Graphs     the live values over the last 2, 6 or 15 s. Live / Freeze.
    Event log  every change and warning; filters All / Changes / Warnings, Pause, Clear
    Check      what the part is doing and what to look at, each with a verdict (green = fine, amber
    = check, red = wrong)
    Settings   theme, text size, open at Run, window size
    Help       report a bug, suggest a feature, article, updates, donate, forum; Copy diagnostics
    for a bug report

TEST STATUS
V1.0: verified in Proteus 8.5 on 31 Oct 2026 (the demo project as shipped: an A4 sheet, an Arduino UNO V4.0).
What the runs showed (the model's own numbers and the sketch's monitor):
  * The project loads and starts cleanly. Before the runs, the model was fitted in a separate solver
    to the datasheets: CTR at the test point by
    rank (PC817 C: 283 % at 5 mA, 5 V), the CTR curve peaking near 3 to 5 mA, and the PC817's
    switching test (VCE 2 V, IC 2 mA, RL 100 ohm):
    rise 4.2 us, fall 2.9 us against the datasheet's 4 and 3 us typical.
  * U1 (PC817, rank C), the 24 V input: SW1 held put 4.87 mA through its LED (VF 1.10 V); its
    transistor pulled D2 down to 0.10 V, the 10k
    pull-up taking 490 uA. The monitor printed "24 V input: ON" once - the sketch debounces the
    switch, whose bounces the optocoupler passes on.
  * U2 (PC817, rank C), the 12 V lamp: at 25 % the pop-up read the LED as PULSED, 490 Hz, about 25 %
    on (2.33 mA on average); at 100 %,
    9.41 mA in the LED switched 6.72 mA through the lamp at VCE 0.16 V. Its Check page: the load
    needs CTR 71 %, rank C gives at least
    200 % - a 2.8 x margin for the LED's ageing. The lamp, our red LED: 6.7 mA at 1.76 V.
  * U3 and U4 (4N35), timed by the sketch with 47k pull-ups: U3, base open, crossed half its swing
    3.2 us after its LED came on and 138.6 us
    after it went off; U4, with 220k from base to emitter, 3.6 us and 21.9 us - six times faster to
    let go. The sketch, reading the pins
    (which switch at about 1 V in the simulation), printed U3 12 / 48 us and U4 12 / 16 us.
  * The pop-up: Optocoupler (inside the package, CTR against IF with the rank's band), Graphs, Event
    log, Check - all four pages followed the run,
    for all four parts.

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" (TEPOPTO.LIB, TEPRESISTOR.LIB, TEPLED5MM.LIB,
TEPBUTTON.LIB and our Arduino library V4.0, ArduinoV4TEP.LIB, with the ARDUINO UNO V4.0 used by the
demo) to the LIBRARY folder of Proteus, for example:
     C:\Program Files (x86)\Labcenter Electronics\Proteus 8 Professional\LIBRARY
   (use the folder that already holds Proteus's own .LIB files).
3. Copy TEPOPTO.DLL, TEPRESISTOR.DLL, TEPLED5MM.DLL, TEPBUTTON.DLL and TEPARDUINO.DLL from "Proteus
Model Files" to the MODELS folder (...\Proteus 8 Professional\MODELS).
4. Delete TEPOPTO.IDX from the LIBRARY folder if it is there (Proteus makes a new index).
5. Start Proteus. In Pick Devices (P) search "PC817 or 4N35".

RUN THE DEMO
"Proteus Simulation\Optocoupler-Isolation-ArduinoUnoV4.pdsprj" (an A4 sheet) - keep the .hex file
and the DLLs beside the project.
  ARD1:   Arduino UNO V4.0 running Opto_Demo.hex, its serial monitor built in (window "TEP Arduino
  UNO - ARD1").
  U1 PC817: SW1 (our push button) from +24V - R1 4k7 - A, K to GND; C to D2 with R2 10k to +5V, E to
  GND             a 24 V input
  U2 PC817: D9 - R3 390 - A, K to GND; +12V - R4 1k5 - D1 (our red LED) - C, E to GND
  a 12 V lamp
  U3 4N35:  D10 - R5 390 - A, K to GND; C to D3 with R8 47k to +5V, E to GND; B open
  U4 4N35:  D10 - R6 390 - A, K to GND; C to D4 with R9 47k to +5V, E to GND; R7 220k from B to GND
  1. Press Run. Every 3 s the lamp goes to its next level (25, 75, 100 %) and the sketch times both
  4N35s.
  2. Hold SW1 (its pop-up, or the mouse on it): the monitor prints "24 V input: ON".
  3. Compare U3's and U4's turn-off delays: the base resistor lets U4 go six times sooner.
Closed the monitor? Click the UNO's USB port.

WIRING (the same in Proteus and on a real board)
  input:  signal - R - A; K to the signal's ground; C to a pin with a pull-up (10k); E to the
  board's ground
  output: pin - R (330 to 470 ohm) - A; K to GND; the load from its supply to C; E to the load's
  ground
  R for the LED = (V - 1.2 V) / IF, for 5 to 10 mA
REAL HARDWARE:
 * The two sides share no wire: keep their grounds apart, or the isolation is gone.
 * As a switch, the load must need less than IF x the lowest CTR of the rank - leave room: LEDs fade
   with age.
 * A bigger pull-up switches slower (the collector-base capacitance times the gain); on a 4N35 a
   resistor of 100k to 1M from B to E
   makes it let go sooner, at the cost of some CTR.
 * An AC or reversed input needs a diode across the LED: it takes only 6 V backwards.

THE DEMO SKETCH ON THE SERIAL MONITOR (Opto_Demo V1.0, 9600 baud)
There are no commands. The sketch steps the lamp every 3 s, times the 4N35s and reports the 24 V
input.
EXPECTED MONITOR OUTPUT
  Optocouplers - The Engineering Projects
  Lamp at 25 %
  4N35 on / off: U3 12 / 48 us, U4 12 / 16 us

PROPERTIES (double-click the part > Edit Properties)
  Part (VALUE)                     PC817 or 4N35
  CTR rank (PC817, STATE)          no rank (50-600 %), A (80-160 %), B (130-260 %), C (200-400 %), D
  (300-600 %) - printed on the body
Every run starts again from the properties.

LINKS.INI (OPTIONAL)
The Help page cards of the pop-up open web pages. To point them somewhere else without a new DLL,
put a text file named links.ini next to TEPOPTO.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
* The output never switches: the LED is reversed, or IF is too small for the load - check IF x CTR
  against the load's current.
* It switches but slowly: a big pull-up; use a smaller one, or a base resistor on a 4N35.
* The input reads twice per press: the switch bounces and the optocoupler passes every bounce -
  debounce in software.
* LED BURNT: more than 50 mA for too long - a bigger resistor.
* The part is not simulated: TEPOPTO.DLL is missing from MODELS and from the project folder. No UNO
  / no monitor window: TEPARDUINO.DLL is missing, or click the UNO's USB port.

BUG REPORTS AND FEATURE REQUESTS
Please post them in our forum with a screenshot, the Serial Monitor text, the
simulation log and the pop-up's Copy diagnostics text:
  https://www.theengineeringprojects.com/forum/category/pc817-optocoupler-proteus-library

SUPPORT US
This library is free. If it saves you time, please support our work:
  https://www.theengineeringprojects.com/donate

WEBSITE
  https://www.theengineeringprojects.com/

LICENCES AND THIRD-PARTY NOTES
* The model (TEPOPTO.DLL), the symbols and artwork, the other parts of ours in the demo and the
  Arduino Library V4.0 (ArduinoV4TEP.LIB / TEPARDUINO.DLL, with its built-in TEP Serial Monitor
  Advance) are made by The Engineering Projects. The models use only standard Windows libraries; no
  Visual C++ redistributable is needed.
  The C++ source code is not included.
* Arduino UNO V4.0 (ArduinoV4TEP.LIB / TEPARDUINO.DLL, our Arduino Library V4.0 - its
  microcontroller is Proteus's own AVR model): The Engineering Projects,
  https://www.theengineeringprojects.com/2026/10/arduino-uno-library-for-proteus-v40.html
* The .hex file is built from the demo sketch and the Arduino AVR core 1.8.6, which includes
  LGPL-licensed code; its source code is available at
  https://github.com/arduino/ArduinoCore-avr/tree/1.8.6
* Proteus is a product of Labcenter Electronics and is not included. Arduino is a trademark of Arduino SA.
  This library is not made or endorsed by Arduino or Labcenter.

REBUILDING THE FIRMWARE (OPTIONAL)
The HEX file is supplied; Arduino IDE is not needed to run the demo. To edit the sketch, open
Arduino Code\Opto_Demo\Opto_Demo.ino, select Arduino Uno and use Sketch > Export Compiled Binary.
Replace the simulation's .hex with the exported HEX. The sketch needs 4,402 bytes of flash and 214
bytes of RAM.

MODEL SCOPE AND LIMITS
Modelled: the LED and its burn-out, the light as a photocurrent, the phototransistor with its CTR
curve, saturation, dark current and junction
charges (the switching times against the load and a base resistor), the voltage across the gap, the
transistor's heat.
Not modelled: the 0.6 pF across the gap, temperature drift of CTR, the LED's ageing, the gap's
breakdown. The charge stored in saturation is an
estimate: no datasheet figure fixes it.

VERSION
TEP PC817 Optocoupler library V1.0 (Nov 2026). Devices PC817TEP and OPTO4N35TEP (TEPOPTO.LIB /
TEPOPTO.DLL). Demo sketch Opto_Demo V1.0. Demo board: ARDUINO UNO V4.0 (TEP Arduino Library V4.0)
with its built-in serial monitor.