It was only last August that PJRC released Teensy 4.0. At that time, the 4.0 became the fastest microcontroller development board on the planet, a title it still holds as of this writing — or, well, not exactly. Today the Teensy 4.1 has been released, and using the same 600 MHz ARM Cortex M7 under the hood, is now also the fastest microcontroller board. What the 4.1 brings to the table is more peripherals, memory, and GPIOs. While Teensy 4.0 used the same small form factor as the 3.2, Teensy 4.1 uses the larger board size of the 3.5/3.6 to expose the extra goodies.
The now slightly older Teensy 4.0 — released on August 7th of last year — is priced at $19.95, with the new 4.1 version offered at $26.85. It seems that the 4.1 isn’t intended as a replacement for the 4.0, as they serve different segments of the market. If you’re looking for an ultra-fast affordable microcontroller board that lives up to its Teensy name, the 4.0 fits the bill. On the other hand, if you need the additional peripherals broken out and can afford the space of the larger board, the not-as-teensy-sized 4.1 is for you. How big is it? The sample board I measured was 61 x 18 mm (2.4 x 0. 7″), not counting the small protrusion of the micro-usb jack on one end.
Let’s have a look at all the fun stuff PJRC was able to pack into this space.
100 Mbps Ethernet
The big news is that Teensy 4.1 comes with 100 Mbps Ethernet support. To use the Ethernet port, you need to supply external magnetics and an RJ-45 jack. These were left off the board for obvious reasons — even using a jack with integrated magnetics (magjack), it wouldn’t fit on the PCB. Instead, a 6-pin header on the board can connect to an external interface. This also helps keep the price low for those who need the other features of the 4.1 without Ethernet connectivity.
PJRC will likely sell a DIY kit of the required parts in the future, but they don’t have a release date or pricing yet. For now, you can easily build your own using this OSH Park shared project. The parts list is in the project’s description, with the key part being the magjack, which will set you back around $2.55 in single quantities. Those building a board should note that this is an early version, and it turns out that only the 0.1 uF capacitor is necessary. Paul Stoffregen of PJRC told me that he just received a simpler PCB for testing, and will publish the design once it’s has been thoroughly verified.
The Ethernet port is capable of full 100 Mbps speed and supports the IEEE 1588 precision time protocol, which allows synchronization of clocks to within 100 ns over wired connections, enabling some very interesting possibilities. But, aside from that, just the inclusion of Ethernet on a microcontroller board is a big deal. Before this, you basically had two choices if you needed this kind of connectivity: use a powerful single-board-computer like a Raspberry Pi with all the latency and headaches the required operating system brings for doing low-level or real-time tasks, or add a slow SPI-interfaced Ethernet board to an existing microcontroller. Instead, you can now use the 600 MHz Cortex-M7 on this new board to run high-bandwidth, low-latency embedded applications without fighting an OS.
USB Host Port
Teensy 4.1 includes a USB host port broken out to a five-pin through-hole header on the inside of the PCB, as was done on the 3.5/3.6 versions. The port will do 480 Mbps high-speed USB. It also adds the power management required for hot-plugging USB peripherals — just add a USB host cable, and you’re good to go. PJRC sells these cables, or you can use a USB2 cable scavenged from an old PC: the pinout is the same. The older Teensy 4.0 only has the USB data lines broken out to surface-mount pads on the PCB.
microSD Card Slot
Like the Teensy 3.6, the new 4.1 board has a microSD card slot on one end to add removable storage. While the pins for this are broken out on the older 4.0 version, the inclusion of this socket greatly simplifies using the interface. And this isn’t like some of the microSD card interfaces you may have seen where you can only use the slower SPI protocol to access the card; here you can use fast, native SDIO.
Teensy 4.1 has 8 MB of flash memory for program storage, up from the 2 MB on the 4.0 version, quite an enhancement. The microcontroller on the Teensy 4.1– an IMXRT1062, same chip as on the 4.0 — comes with 1 MB of on-chip RAM. It’s easy to think of this as a lot for a microcontroller, at least until you think about the power of this 600 MHz 32-bit processor and what people will want to do with it: audio and graphics applications can easily chew through the 1 MB, as can emulation of other processors/systems, such as for retro gaming. So, the Teensy 4.1 allows addition of either or both of two user-supplied extra memories. On the bottom side of the PCB, there are two SOIC-8 footprints: the one with larger pads will accept a QSPI flash memory, while the smaller footprint is intended for an 8 MB PSRAM (pseudo-static RAM) part. You just solder the part(s) on, and you’re ready to go. Thankfully, they’re both SOIC, which these days is considered by many a joy to hand-solder.
A key feature of these additional memories is that they have a dedicated QSPI bus, which doesn’t slow down the Teensy 4.1’s internal program memory. This is especially important for use with flash memory, due to the long erase and write access, which could otherwise bog down a shared bus. Again, by making these parts optional, and user-supplied, PJRC has reduced the cost of the board for those that don’t need the feature(s); those that need them can bring their own memories.
The 4.1 Breaks Out a Full 16-bit GPIO Port
One invariable rule of microcontrollers is that you always need a few more pins. While the processor common to both the Teensy 4.0 and 4.1 has a lot of them, the smaller size of the Teensy 4.0 limited the number of I/O that could be brought out to through-hole headers.
The solution on Teensy 4.0 was to add surface-mount pads for some of the I/O. On Teensy 4.1, the luxurious board real estate allows many more pins to be broken out to headers on the board edge. This brings out an additional serial port, for a total of eight, plus additional analog and digital I/O. The new board also breaks out a full 16 contiguous bits of a GPIO port, which allows for fast, wide parallel I/O. If you’ve ever tried doing this using bits cobbled together from multiple ports, you’ll definitely appreciate not only the convenience, but also the speed this brings to port access.
So, what’s the value proposition here over the older Teensy 4.0? If you really want to take full advantage of the hardware available on the IMXRT1062, the 4.1 is the way to go: the larger stock and optional memories, extra pins broken out, Ethernet port, and convenience of the microSD socket and USB host port make this much easier. If you don’t need these extras, or simply need the smaller board size, the Teensy 4.0 is still around, and will save you a few bucks.
If you need a refresher on what the Teensy 4.0 brings to the table, and which the 4.1 builds on, check out our review of that version.