A LoRa simulator: two SX1278 radios and two Arduinos
Mokxi is a free online LoRa module simulator that runs in your browser, with nothing to install and no account needed. Two Arduino Unos, each with an SX1278 LoRa radio on its SPI pins, running the sender and receiver sketches of the Arduino LoRa library. One sends a numbered hello every two seconds; the other prints it, with no wire between the two radios.
- 505parts on the bench
- 45boards running now
- 1.00xreal time, on every board
What you can do here
In the circuit above, or in the editor it opens.
- Send packets between two boards with the Arduino LoRa library
- Wire an SX1278 the standard way: NSS 10, RST 9, DIO0 2 and the SPI pins
- Read each packet and its RSSI on the receiver
- See how long a packet spends on the air
- Change the frequency in one sketch and watch the link go silent
- Write and test both ends of a link before you buy two modules
What the running circuit shows
A sender, a receiver and 46 milliseconds of air.
Each radio takes seven wires: 3.3 V and ground, NSS on pin 10, reset on pin 9, DIO0 on pin 2, and the SPI clock and data lines on 13, 12 and 11. The left board prints “Sending packet: 0”, then 1, then 2, one every two seconds. The right board prints “Received packet ‘hello 0’ with RSSI -45”, and so on, as each arrives.
The sender also times itself: “on the air for 46 ms”, sometimes 47. That is long for seven bytes. LoRa spreads each bit across a wide chirp so that a receiver can dig it out from under the noise, and airtime is the price. It is the trade at the heart of LoRa, range for speed, and it is why a LoRa link suits a sensor reading every minute and not a video stream.
How the SX1278 is modeled
The registers and the timing, with a perfect sky.
The radio answers the library over SPI as the chip does, and packets take the airtime their settings give them. Every radio on the canvas shares the same air, and two radios hear each other only if their settings match: the frequency, the spreading factor, the bandwidth and the sync word. Change the frequency in one board’s sketch and the receiver prints nothing, the commonest reason a real LoRa pair stays silent.
What it leaves out is distance. Every packet arrives, and the RSSI is always -45; there are no walls, no range limit, no interference and no collisions between senders. LoRaWAN, the network layer with gateways and keys, is not part of this: the circuit is plain radio to radio. On hardware the SX1278 is a 3.3 V part and must never be powered without its antenna.
Three steps from a blank tab to a running circuit.
Open the editor
It runs in your browser tab. Nothing to install, and you need no account to start.
Your first projectWire it and write the code
Drag parts onto a breadboard, run each wire from pin to pin, and write the sketch beside it.
WiringPress Run
Your sketch compiles in the tab and runs on a model of the chip, with the Serial Monitor beside it.
Run and serial
Open a project and press Run.
Every one runs in the editor exactly as it is drawn, ready to change.
What makers say about Mokxi.
“The AI checker helps check and correct my circuits, and it has way more components than Tinkercad. As a student I really appreciate the tool.”
“I’d been looking for a real online electronic simulator that was intuitive and complete when I found Mokxi. I was able to quickly import a Fritzing file and my Arduino sketch and start testing. Mokxi has all of the makings for the best online Arduino simulator I have been able to find!”
“I’m using Mokxi to develop and simulate an STM32-based four-wheel-drive robot car before building the actual hardware. It allows me to experiment with DC motor control, PWM, RPM measurement using photointerrupters, and different acceleration, braking, and reversing strategies, helping me understand and refine the system before implementing it in real life.”
Questions, answered.
Is it free?
Yes. The circuit on this page, every part in it and the editor it opens in are on the free plan, with no card.
Do I need an account?
No. The circuit runs the moment the page does, and the editor opens without one. A free account is only for saving a project to the cloud and sharing it by link.
Can I simulate LoRa communication between two Arduinos?
Yes. That is the circuit above: two Unos, two SX1278 radios and the Arduino LoRa library’s sender and receiver, with no wire between the radios. Range and interference are not simulated; every packet arrives.
Why is my LoRa receiver not getting packets?
Most often the two radios’ settings differ: the frequency, the spreading factor, the bandwidth or the sync word. Next most often it is wiring, NSS, reset or DIO0 on a pin other than the one the sketch names. Change the frequency in one sketch here to see the first case.
Is this a LoRaWAN simulator?
No. It simulates the LoRa radio itself, point to point between modules. LoRaWAN gateways, network servers and device keys are not modeled.
Do I need an account at all?
No. The editor, the templates, the gallery, the compiler and Run all work without signing in. Your browser keeps your work as you go. An account saves your projects online, so they follow you to any computer. It also gives you a link to share.
Which boards are supported?
Forty-five, all on the free plan. Arduino: the Uno R3, Uno R4 Minima and Uno R4 WiFi, Nano, Nano ESP32, Nano RP2040 Connect, Mega 2560, Leonardo, Micro, the Pro Mini in its 5 V and 3.3 V builds, and the SparkFun Pro Micro. ESP32: the classic DevKit V1, the ESP32-S3, the ESP32-C3 and C6 DevKits, the Espressif DevKitC V4, the Freenove ESP32-WROVER, the Wemos LOLIN32 Lite, the Wemos D1 R32, the Cheap Yellow Display, the TTGO T-Display, the ESP32-C3 SuperMini and the Seeed XIAO ESP32-C3, C6 and S3. ESP8266: the NodeMCU, the Wemos D1 mini and the ESP-01S. Also the Raspberry Pi Pico and Pico W, the Seeed XIAO RP2040, the Waveshare RP2040-Zero, the Seeed XIAO SAMD21, the WCH CH32V003, the STM32F411 Black Pill, the STM32 Nucleo-F411RE and the STM32F103 Blue Pill, the BBC micro:bit V2, and the ATtiny85 and the ATmega328P in its 16 MHz and 8 MHz builds, which plug straight into the breadboard as bare chips. Your own code compiles in the browser for all of them. Then the Raspberry Pi 4, Pi 5 and Zero 2 W computers, which run your Python with gpiozero and RPi.GPIO, with nothing to compile. Each board page lists what it can and can’t do. For example, the WiFi boards have pretend WiFi, not a real radio, and the page says so.
Is my sketch really compiled in the browser?
Yes. A real compiler (clang, built for the web) runs in your browser. It downloads once, and your browser keeps a copy. After that, every build happens on your own computer. There is no build server and no waiting in line, so there are no build minutes to run out of.
Which browsers work?
Any up-to-date Chrome, Edge, Firefox or Safari, on a computer, a phone or a tablet. They all support WebAssembly, which Mokxi needs, and they have for years.
Does it work on a phone?
Yes. The editor works with touch, the buttons are big enough to tap, and the layout fits a small screen. The simulation runs on the phone itself.
Can I try Pro before I pay?
Yes. Every account can try Pro free for 7 days, once. It takes a card, nothing is charged for those days, and if you cancel before they end you pay nothing. It starts when you choose it.
Can I cancel anytime?
Yes, in one press from your account page. Your plan runs to the end of what you paid for.
Do you offer refunds?
Yes, once per account. Write to us within 14 days of a payment and we refund all of it. Lifetime Pro is refunded in full within 14 days of buying it.
Is there a student discount?
Yes. Students get Pro at half price with a school email.
Do students need accounts?
No. The simulator works signed out, so your class starts from one link with nothing to sign up for. An account only adds cloud saving and sharing, and a student can make one later, or never.
Does it work on a Chromebook?
Yes. Everything runs on the machine in front of the student, so a Chromebook works as well as a lab PC.
What does it cost for a class?
Nothing, if your students only need to open and run circuits: the whole simulator is on the free plan. The class tools (a roster, starter projects, auto-graded checks, the gradebook) come with Pro and Classroom. Classroom is $9.99 a student a year, from 5 students, so at least $49.95 for the year. Your own seat is free, and from 50 students each one costs less. Your students get Pro’s room while they are in your classes. Pay by card, invoice or purchase order. Pro on its own runs classes for up to 10 students in all. To try the class tools with real students first, start the free 30-day trial from your class page: one class of up to 20 students, no card.
Is student work private?
Yes. A student’s projects in a class are always private: they cannot be opened by link or put in the gallery. One exception, and only for reading: a teacher may open, and never write, a project owned by somebody in a class they teach, which is what a card on the class wall does. What we store about a student, who processes it, how a school has it deleted, and how we handle COPPA consent for students under 13 and FERPA as a school official are all on the student data privacy page at /privacy/students.
Is Mokxi AI free?
Every signed-in account gets questions every day: 5 on a free account, 50 on the Pro trial, 100 on Pro and the other paid plans, and 25 on Lifetime Pro.
Does Mokxi AI work with ESP32 and Raspberry Pi Pico sketches?
Yes. It knows which board the project is on and answers for that board, from an Uno to an ESP32, an ESP8266, a Pico or an STM32.
Can Mokxi AI change my code without asking?
No. It proposes a change as a card. Accept is yours, and only appears once the changed code compiles; Ctrl+Z undoes it.
What does Mokxi AI send with a question?
Your project text, the matching help articles and the last six messages of the chat, never your name or account. "What is sent" shows exactly what went.
Latest arrivals in Mokxi.
More simulators
Each one opens on a circuit that is already running.
Send a packet
Open the circuit and watch the hello arrive on the other board. Nothing to install, and no account needed.