Raw Speed & the FPU

Both boards share the same 600 MHz Cortex-M7 with hardware single- and double-precision floating point, dual-issue execution and 32K caches. If your code does FFTs, PID loops, filters or matrix maths, that FPU is the whole reason to buy a Teensy over an 8-bit or M0+ board.

Pin Count & Peripherals

Teensy 4.1 gives you 55 I/O (42 breadboard-friendly), 35 PWM, 18 analog inputs and 8 serial ports. Teensy 4.0 gives 40 I/O, 31 PWM, 14 analog and 7 serial. Both carry 3 SPI, 3 I2C and 3 CAN buses (one with CAN FD) — count your peripherals before you pick.

Memory & Expansion

Both have 1024K RAM (512K tightly coupled to the core). The 4.1 has 8 MB flash and 4284 bytes of emulated EEPROM against the 4.0’s 2 MB and 1K — and adds two QSPI pads where you can solder extra PSRAM or flash for audio buffers and frame buffers.

Connectivity You Actually Need

Teensy 4.1 has a 10/100 Mbit DP83825 Ethernet PHY, a native SDIO micro SD socket and a 5-pin USB host header on board. Teensy 4.0 exposes USB host and SD only as bottom SMT pads. Neither board has Wi-Fi or Bluetooth — plan an ESP32 or module if you need wireless.

Size, Pins & 3.3V Logic

Teensy 4.0 is 35.6 × 17.8 mm; the 4.1 is 61 × 17.8 mm. Buy the “with pins” version if you want to breadboard today, the bare version if you’re soldering into a product. And remember: 3.3V I/O only, not 5V tolerant, roughly 100 mA at full clock.

Exactly the same Teensy 4.0 board, but with the header pins already fitted at the factory. If you don’t own a soldering iron — or you simply want to be prototyping ten minutes after the box arrives — this is the version to order. It drops straight into a breadboard with a row free on each side, and the small premium over the bare board is usually less than the cost of a decent pin-header strip and your time. The trade-off is that permanent installs get messier: once pins are on, you’re soldering wires to pins rather than flat to pads.

The bare Teensy 4.1 is the version you want when the board is going inside something. With no headers fitted you can surface-mount it flat onto a carrier PCB, solder ribbon directly to the pads, or fit low-profile right-angle headers of your own choosing — and you keep clear access to the bottom-side SMT pads, the two QSPI memory footprints for PSRAM, and the SD card signals. It’s the same 8 MB flash, 55-pin, Ethernet-and-SD board as our top pick, just left for you to finish. One honest caveat: this particular ASIN is often fulfilled by third-party marketplace sellers, and its price swings much more than the with-pins listing, so check it against PJRC’s own store before ordering.

This is the piece most people don’t realise they need. The Teensy 4.1 has a DP83825 10/100 Mbit Ethernet PHY built into the board, but the RJ45 magnetics jack is not — the six Ethernet signals come out on a small pad group instead. This kit supplies the RJ45 MagJack adapter board, a 6-pin ribbon cable and the header pins to connect the two. Solder the 6-pin header to your Teensy, plug in the cable, and you have real wired networking with the NativeEthernet / QNEthernet libraries — ideal for OSC, Art-Net lighting, Modbus TCP and industrial data logging where Wi-Fi simply isn’t acceptable.

The single best reason to own a Teensy. The Rev D audio adaptor adds an SGTL5000 codec with stereo line in, stereo line out, a headphone amplifier, a microphone input and a microSD socket — and pairs with PJRC’s Teensy Audio Library and its drag-and-drop graphical Audio System Design Tool. Combined with the M7’s floating-point unit you get polyphonic synthesis, real-time reverb and filters, WAV playback from SD, FFT analysis and multi-channel mixing with CPU headroom to spare. Note that Rev D is the Teensy 4.0/4.1 version — the older Rev C is for Teensy 3.x and won’t line up correctly.

Electrically this is an ordinary Teensy 4.0, but it ships in the state that lets you use the i.MX RT1062’s secure boot fuses. You write your own AES key, compile your sketch to an encrypted EHEX file, and lock the chip so it will only ever run firmware signed with that key — nobody can read your code back out or flash their own onto the board. That matters if you’re selling a product, entering a competition, or shipping a client build you’d rather not see cloned. Treat it as one-way: once the fuses are blown the board is permanently locked to your key, and losing that key bricks your ability to update it.

Dupont jumpers are fine on a bench and terrible in a machine. This carrier board takes a headered Teensy 4.1 and brings every pin out to a labelled screw terminal, with mounting holes so the whole assembly bolts into an enclosure or control panel. Field wiring goes in with a screwdriver and stays put through vibration — exactly what you want for CNC controllers, sensor cabinets, test rigs and anything that has to survive being moved. A DIN-rail version of the same board is also available if you’re building into a control cabinet. The Teensy itself is not included.

Building a synth, effects pedal or recorder?

Take a Teensy 4.1 plus the Rev D audio shield. The extra flash holds samples, the SD socket streams WAVs, and the QSPI pads let you add PSRAM for long delay lines.

Logging fast sensor data?

The Teensy 4.1‘s native 4-bit SDIO micro SD socket is dramatically faster than SPI card modules — it’s the reason the 4.1 dominates data-logging and telemetry builds.

Driving motors, CNC or robotics?

Either board works — 31–35 PWM channels and 3 CAN buses are plenty. Choose the 4.1 if you need more than about 20 pins, and add the screw-terminal breakout for the finished machine.

Need wired networking?

Only the Teensy 4.1 has the Ethernet PHY — pair it with the Ethernet kit for Art-Net, OSC, Modbus TCP or plain HTTP over a cable that never drops.

Squeezing into a tiny enclosure?

The Teensy 4.0 is 35.6 × 17.8 mm and delivers identical compute. Buy the bare version and solder wires flat for wearables, drones and handheld builds.

Selling a finished product?

Use the Lockable Teensy 4.0 and encrypted EHEX firmware so your code can’t be read out or cloned — just guard the AES key like a private key.

Need Wi-Fi or Bluetooth?

Then don’t buy a Teensy for that job. No Teensy 4.x has a radio — use an ESP32, or bolt one on over serial and let the Teensy do the real-time work.

Teensy 4.1 vs Teensy 4.0 — which one should I actually buy?

They run the identical 600 MHz Cortex-M7, so raw speed is a tie. Buy the 4.1 if you need any of: more than ~35 usable pins, a micro SD card socket, wired Ethernet, more than 2 MB of flash, expandable PSRAM, or a proper USB host header. Buy the 4.0 if none of those apply — it’s noticeably cheaper and half the length, which matters more than people expect once the board is inside an enclosure. As a rule of thumb: audio, data logging and networked builds want the 4.1; sensors, motor control and compact gadgets are perfectly happy on the 4.0.

Does the Teensy 4.1 have Wi-Fi or Bluetooth?

No — and neither does the Teensy 4.0. PJRC spent the silicon budget on compute and I/O rather than a radio. The 4.1 offers wired 10/100 Ethernet (with the add-on kit), which is more reliable for industrial and stage use anyway. If you need wireless, the usual pattern is to pair a Teensy with an ESP32 or an ESP8266 module over a serial port: the ESP handles the network stack while the Teensy does the hard real-time work. For a purely wireless project, buy an ESP32 instead — it will cost a fraction as much.

Are Teensy 4.x pins 5V tolerant?

No. Every I/O pin on Teensy 4.0 and 4.1 is 3.3V only and will be damaged by 5V — unlike the older Teensy 3.2, which was 5V tolerant. This is the number one cause of dead Teensy boards. Use a level shifter (or a simple resistor divider on inputs) for 5V sensors, character LCDs, older shields and RS-232 adapters. You can still power the board from 5V through the VIN pin or USB; it’s the signal pins that must stay at 3.3V. Note also that the 3.3V regulator has limited headroom for driving external peripherals, so budget your current.

Can I program a Teensy with the Arduino IDE?

Yes. Install Teensyduino, PJRC’s add-on for the Arduino IDE, and the Teensy appears as a normal board with the familiar setup()/loop() sketch model and most standard Arduino libraries. PlatformIO also supports the Teensy 4.x platform directly and is the better choice for larger projects. Uploads go over the same USB cable via the Teensy Loader — no external programmer needed. You also get Teensy-specific extras such as USB MIDI, USB keyboard/mouse/joystick modes, the Audio Library, TeensyThreads and easy clock-speed selection (including overclocking above 600 MHz, which needs a heatsink and is not guaranteed on every chip).

Do I need the Ethernet kit, and can I add PSRAM to a Teensy 4.1?

The Ethernet PHY is already on the Teensy 4.1, but the RJ45 magnetics jack is not — so yes, you need the Ethernet kit (or an equivalent MagJack breakout) plus a soldered 6-pin header before you can plug in a cable. Separately, the 4.1 has two QSPI footprints on its underside where you can solder extra memory: typically a PSRAM chip for large audio buffers, video frame buffers or big data arrays, and/or an extra flash chip for sample storage. Both are optional user-installed upgrades and need surface-mount soldering, so plan for them before you commit the board to an enclosure.

Why are Teensy boards so much more expensive than an ESP32 or a Pico?

Because you’re paying for a much larger microcontroller, a small-batch US-assembled board and a genuinely maintained software stack rather than a commodity module. The i.MX RT1062 is a crossover applications processor, not a low-cost MCU. Whether that’s worth it depends entirely on your project: if a 150 MHz Pico 2 finishes your workload with room to spare, buy the Pico. If you’re doing real-time floating-point audio, sampling at hundreds of kilohertz, or driving thousands of addressable LEDs, the Teensy will do it when nothing else in this price bracket can. One tip: Amazon prices on Teensy listings vary a lot by seller — always compare against pjrc.com and authorised distributors before ordering.