While supplies last, buy any "Last Chance" board, and get a free Rev. C bare PCB absolutely free! This includes all aitoreset supported 0-series and 1-series boards (the autoreset isn't exactly useful except in unusual situations owing to the lack of a reset pin for it to connect to; we now only include the autoreset circuit on parts that let you have a reset pin and a UPDI pin at the same time), as well as all 16k boards.

I'm happy to report that ALL of our current stock of ATtiny3226 assembled boards is known to have been built with the high-temperature spec parts (we always try to do this - the price difference is small; while it may not be likely that anyone is going to use this board at such temperatures, the higher spec translates directly to more headroom on key specs, permitting more extreme overclocking, or continued functioning at a given clock rate as the voltage droops further below what the datasheet says is required (this headroom is in any case quite generous around 25C.

Convenient, basic development/breakout board for 20 pin modern tinyAVRs like the ATtiny3226 or 3216

Over the past half decade Atmel/Microchip has been releasing AVR microcontrollers based on an all new set of peripherals, the megaAVR 0-series and tinyAVR 0/1/2-series, as well as the newer Dx-series and Ex-series. These use the familiar AVR instruction set and open source avr-gcc compiler used with the classic AVR microcontrollers, but with redesigned and more capable on-chip peripherals and highly competitive prices. The AVR instruction set has been given a tuneup but nothing drastic - just timing improvements; with a handful of the most important instructions getting 1 clock faster (ST/STD, PUSH and CBI/SBI are the ones that matter, they are all 1 clock instead of 2 now; ). The best known of these (among hobbyists, at least) is the ATmega4809, used on the Arduino Uno WiFi Rev.2 and Nano Every. However, there is also an extensive line of tinyAVR parts based on this new architecture - with my megaTinyCore, there is full Arduino IDE support for these, and almost all libraries are either compatible, or have a compatible bundled version included with the core.

The ATtiny 2-series marks the first AVR release with a proper differential ADC (the one on the Dx-series didn't let the voltage go over VREF and had no gain stage, so you couldn't do anythign with it that you couldn't do with 2 simultaneously triggered normal ADCs. Which was entirely possible to rig up on the 1-series, actually...). The top-end 20-pin part of the 2-series is the ATtiny3226, now available (well, it's on backorder like every other part these days, but we've got a fair number), as well as some left over ATtiny 1626's (the 16k version). They appeared on the market first, followed by the smaller versions, and finally by the full 32k ones. The ATtiny3216 meanwhile is the top-end 20-pin tinyAVR 1-series device, with 3 analog comparators, an 8-bit dac, a very unusual dual ADC, and the high speed timer TCD0.

These breakout boards come equipped with your choice of 3.3v or 5v regulator (LDL1117) so that it can be supplied with an external supply (minimum dropout as low as 0.35v!) using the two pins in the lower left corner, an LED (on PA7, Arduino pin 3), and a UPDI programming header (with the ~4.7~ 470 resistor on the board, which can be bypassed with the RBP solder bridge jumper on the back). There is a 1x6 pin "FTDI"-style serial header on the bottom edge of the board. One of the exciting features on 20 and 24-pin 2-series is an optional alternate reset pin! You can use PB4 as reset now.

That means that 2-series boards are made with the autoreset circuit parts installed, and the are shipped with them connected to PB4. This can be disconnected by clearing the solder bridge on the underside of the board.

All pins are broken out, and there are 3 Vcc and 3 Gnd pins available, plus the ones on the UPDI and Serial headers so even if you're not using breadboard, you can still easily connect power and ground for multiple external devices.

Board dimensions are 1.4" x 0.85" with the rows of pins 0.7" center to center for the Rev. B. Rev. C boards (with the darker solder mask for more readable silk) are 0.7625" wide (19.37mm), with the rows of pins 0.6" center to center, so you can use them with wide DIP sockets should you wish to. Rev. D, which has not yet been designed, has 3 planned changes thus far - width will be extended a hair to 20mm, which gives a bit more space to make legible silkscreen around the pins, though the positions of holes will remain unchanged relative to each other), a Reset/User button directable to either PB4 or PA0 (the two possible reset pins) by the same solder bridges as autoreset), and a few layout tweaks to improve assembly.

This is available as a bare board (supporting all the x26, x16 and x06 parts) here. Want to make lots of them? Buy out our inventory of Rev. B boards, get our own stainless steel stencil (a $25 value) FREE!

ATtiny3216 features and Arduino support

• 32Kb flash, 2k SRAM
• 17 available I/O pins
• 6 PWM pins with 8-bit resolution.
• Servo, Tone, Serial, SPI and Wire (I2C) support "just works".
• 2 Type B timers - so Servo and Tone can both be used simultaneously, or one or both can be taken over for input capture, periodic interrupt, or other functionality.
• DAC output (just do analogWrite() on the DAC pin - voltage is between 0V and the DAC reference voltage; that can be set to any of the internal ADC references with the DACReference() function; no, you can't use the supply voltage as the DAC reference).
• 1 type D async timer, which gives two additional PWM pins. Because manually reconfiguring this timer is a right pain in the arse and few people are likely to attempt it, megaTinyCore defaults to using it for millis, which won't interfere with PWM, though the other timers can also be used (TCBs are strictly better for this purpose, but are so useful and limited in number on the tinys that we wouldn't default to wasting them on a background functionality like millis, while the TCA is usable as well - there's a tools submenu to select the desired timer)
• 11 analog inputs (not counting PA0, which is on the UPDI pin - though it can be used in a pinch)
• A SECOND ADC, ADC1. megaTinyCore doesn't configure or interact with it in any way... So you could put ADC1 into freerun or WCOMP made, while continuing to use analogRead elsewhere (which uses ADC0)
• Internal clock at up to 20MHz at 5v, up to 10MHz at 3.3v (in practice, they can be run considerably faster, and the internal oscillator has an incredible degree of compliance; they stop working around 30 MHz, which is usually within range of the internal oscillator)
• Configurable custom logic: you get a pair of 3-input "Configurable Custom Logic" blocks which can be be entirely asynchronous (faster than the system clock). The inputs can be taken from pins, the event system, or from a number of internally generated signals from most peripherals (you can, for example, output the logical AND of two PWM signals like the output compare modulation feature on some classic AVRs - these timer inputs are probably the most useful). The core includes the Logic library, which provides a consistent interface across all modern AVR parts, including a number of examples, including squeezing an extra PWM channel out of TCD0, and
• Event system - 6 channels that can route certain events between peripherals (this, for example, is how you do input capture now - instead of there being a single pin that's also the only pin for other important things, you use the event system to route any pin to a timer. megaTinyCore includes the Event library which provides a consistent interface across all of the modern AVRs (the behavior of logic changed significantly between the 0/1-series and... basically every other modern AVR).

ATtiny3226 with super-fancy new ADC

The newest 20-pin tinyAVR is the 3226, a member of the tinyAVR 2-series. The 2-series is very nearly 100% pin compatible. (code that uses the event system will need modifications - though they will tend to make code simpler - the 0/1-series event system was a real mess; the 2-series has a normal Dx-ey event system identical to what the AVR Dx-series parts have (actually, in a subtle way, it's better). It has two additional CCL LUTs, a second USART,and the modernized event system - but the real point of the 2-series was the new ADC. There's only one now, but it has 12 bit resolution instead of 10, and is now able to take true differential measurements. and has a programmable gain amplifier, auto-sampling (and easy oversampling and decimation that comes with it) has been extended to 1024 samples. Another much anticipated feature is the support for setting PB4 as an alternate reset pin, as the 1-series couldn't get a real hardware reset pin unless they sacrificed easy UPDI reprogramming.

We are now selling the latest version of our breakout board, the Rev. C, with a 3226 mounted on it. The Rev. C boards boast improved silkscreen on a higher contrast solder mask, more flexible solder bridge jumper options for configuring autoreset support, and pads to add an external clock in 3225 (3.2mm x 2.5mm 4 pin, standard pinout) package and it's decoupling cap if you happen to need one - all in a narrower form factor than the Rev. B (It's now the same width as a nano, and hence fits popular prototyping boards or a wide DIP socket.

We also have a number of 1626 boards for sale; these have 2k of RAM and 16k of flash, instead of 3k and 32k, but are otherwise identical. These boards date to prior to the clearing of the chip shortage backorder queues in 2023, first during the time between the 1626 and 3226 release and later when 3226's had backorder queues a year long. In the absence of unexpected difficulty sourcing 3226's, we don't plan on restocking them once they are sold, and as such have marked them as last chance. The same last-chance free-bare-board deal as we offer on the remaining 1606 inventory applies here.

Differences between 3226 and 3216

• A single MUCH fancier ADC - a lot more useful than two copies of a more basic one. 12 bit resolution, capable of true differential measurements, faster conversions, and with a programmable gain amplifier, the first release since Microchip bought out Atmel to feature any of those. It has hardware accumulation so you can do oversampling and decimation from a single "start conversion" command to sum up 1024 readings, which can then be "decimated" to get a 17 bit result. And unlike most Arduino cores, megaTinyCore exposes that functionality through a few simple new functions, while still maintaining backwards compatibility so analogRead() works normally - taking that aforementioned 17-bit accumulated reading is as simple as analogReadEnh(pin,17); ("enhanced analog read of 'pin' to 17 bits of resolution") - or if you wanted that to be a differential reading? analogReadDiff(positive_pin,negative_pin,17); You wanted to amplify that by 16x using the PGA too? `analogReadDiff(positive_pin,negative_pin,17,16); - there is a detailed reference for the exposed functions surrounding the ADC included with the megaTinyCore readme Of course, analogRead(pin) will still by default give you a 10-bit reading, though you can, as usual, switching between the resolutions supported in hardware for a single conversion (8 or 12 - the 10 is a compatibility shim that takes a 12 bit reading and drops the two LSB). I make no claims as to how many of those extra bits you get from oversampling and decimation are noise vs signal - it doesn't take much to throw off a 17-bit ADC measurement, and will likely need to take extra power supply filtering measures to make the most of the new ADC. However, even without that, it is significantly more capable than the 1-series ADC
• 32k flash, 3k SRAM)
• A second hardware serial port
• Same PWM, Servo, Tone, Wire, SPI libraries work
• 2 type B timers (all the 2-series have this now)
• No DAC, No Type D timer
• Only 1 analog comparator
• Twice as many CCL logic blocks or "LUTs" (Microchip likes that abbreviation, which refers to the truth look-up tables for the logical operation)
• The 1-series comes in in N and F temperature specs (-40C - 105C or 125C). The 2-series comes in U and F specs (-40C - 85C or 125C). Good news - I managed to score stockpiles of the high temp parts. Why does this matter if you're not running above the boiling point of water? Well, they do tend to overclock better, if that's your thing. These parts can be overclocked as high as 30 (1-series) or 32 (2-series) using the internal oscillator by running a tuning sketch, provided it runs from a stable 5v power source and is at room temperature.

ATtiny1606 (Say good bye)

The ATtiny1606 is the top-end 0-series part in a 20-pin package, but top-end 0-series is still 0-series. The 0-series is intended for low cost applications, and cuts a few (well, kind of more than a few) features; it also didn't do very well at lowering the cost, which was already low. So, for hobbyists and one-off projects, the 1606 is not a compelling choice, and unsurprisingly, they did not sell very well. So these are only really of interest if prototyping for something that will use a 0-series for the small cost advantage. From now until we sell out of the 1606 boards, they come with a free bare Rev. C board as a promotion. They will not be restocked.

Recommended Pins

In some of the pictures shown above, the boards are shown with pin header (not included) attached. We recommend:

• For prototyping w/out breadboard: Two 1x9 pin male pin header for the rows of pins on the sides (in picture, 1x6 in black, for the I/O pins, 1x3 green and red for ground and vcc pins - colored pin header can be had cheaply on ebay, and makes it easier to avoid mistaken connections)
• For use with breadboard 2 1x9 "machined" pin headers are recommended. The full-size 0.1" header deforms the clips in the breadboard, making the holes it is plugged into unreliable when using things with smaller pins.
• A 1x6 pin header for the serial port (standard FTDI pinout) - I recommend 90-degree angled male pin header.
• A 1x3 pin header for UPDI programming - I find straight pin header more convenient on breadboard (so the cable doesn't get in the way as much), and angled header more convenient if not using breadboard (for the same reason).

We offer an optional colored pinheader kit containing: 1x3 red and green - for the Vcc and Gnd pins 2 pcs 1x6 - for the I/O pins 1x6 yellow, 90 degree angle - for the serial adapter 1x3 white, 90 degree angle - for connecting a UPDI programmer These are all cut using a precision slicer, so they fit up against eachother easily (you can't break or cut them with plain wire cutters if you want it to look good.)

Programming the tinyAVR 0/1/2-series parts

There are two approaches to programming these parts:

UPDI

Unlike "classic" AVR microcontrollers, these new parts are programmed via a "UPDI" single wire interface instead of the SPI-based ICSP protocol. You can easily make a UPDI programmer from (almost) any serial adapter with a schottky diode or 4.7k resistor, (I found that the diode worked far better - some people disagree and the matter has not yet been fully explained). As of the most recent releases of my megaTinyCore which improved performance using this method (it now leaves jtag2updi and Microchip's official programmers in the dust), this is what we recommend; see the instructions here;

The 2.4.0 release has further improved compatibility with a wide range of serial adapters by ensuring that the non-TURBO mode (turbo mode being "go faster at all costs, including buying inexpensive serial adapters (Blue DeekRobot FT232RL and black CH340G with voltage switch are both great adapters for this); the DeekRobot RT232RL boards even have an A that don't suffer from implicit latency) does not implicitly use the USB latency to give the chip a chance to perform the page write, making it work with (almost) all adapters. The performance will fixed back up in a future version to get rid of most of the performance penalty (up to 1 second per upload).

Make UPDI programmer from either a serial adapter and a diode, or a Nano/ProMini/Uno

The order of the pins on the UPDI header is UPDI-Gnd-Vcc - this means that if the programmer is connected backwards, the board will not be damaged. The 470 ohm resistor is compatible with all three of the most plausible options: SerialUPDI ( resistor is on the breakout board; you do not need to (and should not) use another one.

A typical development configuration might have the board connected to a serial port via the 6-pin serial header for serial debug, and to the UPDI programmer via the 3-pin header for uploading new code (as shown in the pictures). This is generally how we use it, and is what we recommend.

Serial (Optiboot bootloader)

The Optiboot bootloader is supported for all parts; this works with an external serial adapter (like the 6-pin ones used for the Arduino Pro Mini). Optiboot takes up 512b of flash for the bootloader. In addition to obliviating the need for a UPDI programmer to upload sketches (though note that the same serial adapter could also be used as a UPDI programmer, Optiboot allows you to use the same port for upload and serial monitor like a normal Arduino board.

There are two general approaches to using Optiboot on these parts and a third, much better way on 2-series parts:

1. Without auto-reset, UPDI enabled. On all boards that do not support auto-reset, and on boards that do if this option is selected, the UPDI/Reset pin will be left as UPDI, and the board can be freely reprogrammed via UPDI. The version of the bootloader installed will be active for 8 seconds after power on, or after a WDT or software reset. So for example, to upload, you would verify sketch, unplug, plug back in, and then upload - or alternatively, you could adapt your sketch to trigger a software reset. UPDI programming will still be possible. Note that for these boards, you must use UPDI to "burn bootloader" with the non-optiboot board definition selected if you want to switch back to uploading sketches via UPDI

2. With auto-reset - using alternate reset pin (2-series only) or by sacrificing UPDI programming (0/1-series). This is recommended if you want to use Optiboot with the 2-series. We do not recommend using this with 1-series parts, as it precludes further UPDI programmer without an HV UPDI programmer which is still somewhat exotic.

Another approach is to upload sketches which all have a means of triggering a "software reset" from within the sketch, either from a pin interrupt (the existing autoreset parts could be wired to this pin). With other trigger mechanisms, this could be used in more advanced deployments, such as a device at the far end of a serial line, which resets in response to a specific command0). These schemes allow one to use the bootloader without powercycling the board while also permitting use of UPDI programming - however because they depend on the sketch, they are inherently more "brittle", and that UPDI programming option may become necessary to revive boards during development - in the event of bugs in the application. This method is beyond the scope of this product listing.

If purchased without the bootloader installed, if you later decide that you want it, you may install it using a UPDI by doing burn bootloader (if using autoreset and UPDI pin set as reset, the jumper on the back must be closed after bootloading); this pre-bootloading service is intended only as a convenience.

Boards with optiboot preinstalled are bootloaded at the time the order is received. All boards are set to 20-MHz derived clock speeds unless 16 MHz is requested, 4.2 sampled BOD, 3.3v boards are set to 10MHz (will also run at 5MHz) 2.6v sampled BOD. No-regulator boards are set to 20MHz/10MHz/5MHz, with BOD disabled to minimize idle power consumption. Because these are bootloaded on-demand, (and the UPDI pin is configured to act as a reset pin if you choose autoreset for a ATtint3216 or 1606 you will not be able to reprogram the fuses without an HV UPDI programmer; thus, if you have different requirements (eg, 16MHz base clock to allow 16MHz/8MHz/4MHz speeds, or different BOD settings), this can be done, just list what you want in order comments.

More information on Optiboot and the tinyAVR 0/1/2-series parts is available in the megaTinyCore documentation.

Regulators and power supply - do I want a regulator?

The linear regulators offered can provide a regulated operating voltage provided Vin in at least 1.3v (ZLDO1117) higher than the operating voltage. These regulators are appropriate when your current requirements are relatively low, and you have access to a power supply with a voltage higher than the operating voltage (max 18v input) - maximum power dissipation, however, is only ~ 1.2W without adding heatsinks, (that is to say (Vin - Vout)*(current) < 1.2W) so the practical maximum current is much lower.

Example calculations of maximum current when using the regulator:

Vin=12v, Vout=5v. Vin-Vout=7V. 7V*I < 1.2W -> I < 1.2W/7V -> I < 170mA

Vin=7v, Vout=5v. Vin-Vout=2V. 2V*I < 1.2W -> I < 1.2W/2V -> I < 600mA

Only the Vin pin goes through the regulator - all other Vcc pins (including the UPDI and FTDI headers) are connected directly to the Vcc rail - so if you have a 3.3v regulator, but connect a 5v serial adapter's 5v line to the board, the board will be running at 5v (this will not harm the board itself, as long as the voltage does not exceed 5.5v - but if you have 3.3V devices connected to it, those may be harmed, so if you have any of those connected, you must use a 3.3v serial adapter or power some other way, and not connect the 5v pin of the serial adapter (the data lines are fine, as serial adapters almost universally have a 1k - 2.2k resistor in series with the TX line, while the RX line is only weakly pulled up and can be handled by the protection diodes which will limit the current to a non-dangerous level, or disconnect the 3.3v devices from the board before connecting the 5v to the board's Vcc), whereas if you supply 5v to the Vin pin, the board will be running at 3.3v.

However - a regulator has a quiescent current that it draws to power itself (0.25mA~0.5mA for these regulators). Hence, if you are running on batteries and using power saving techniques, you want to avoid having a regulator on the board if possible. For example, if running off a LiPo/LiIon battery at 3.7~4.2v, you could set it to run at 10MHz, and use no regulator - approximate power use with a regulator (whether or not you power through the regulator or connect power direct to Vcc), the sleep mode power down current will be ~0.25mA (almost all from the regulator), whereas without the regulator, current in sleep mode power down will be ~0.1uA (0.0001mA) at room temperature - that is, for a project where the chip will spend most of it's time in sleep mode power down, the battery life may be 2,500 times longer without the regulator.

If powering from batteries w/out a regulator, you need to be careful not to connect external power directly to Vcc (including from a serial adapter or UPDI programmer) while the battery is connected.

On boards where there is no regulator, the PTC fuse is still present (in series with Vin), and the regulator is bypassed by a 0-ohm resistor, so you can still use the Vin pin power the board to get the benefit of overcurrent protection. See picture 3 for an example of what the "no regulator" looks like.

Special orders

We can build these with 1.8, or 2.5V regulators in addition to the usual 3.3V, 5V, or bypassed regulator (or it can be left bare if you have some special regulators you want to use for an exotic voltage or ultra low quiescent current and it's compatible with the 1117-SOT223 footprint). Message me to discuss - pricing depends on quantity and delivery time requirements (if you want a full mini-panel of 10 PCBs, great). We can perform tuning to the megaTinyCore conventions (stored in last 12 bytes of the user row for the (tuned) clock speed options), or use whatever speed external clock you want us to if we have it on hand for the required voltage (external clocks have an annoying habit of having insanely narrow specs (4.75-5.25V I've seem, and 4.5-5.5 is common. Or it's 2.0-3.6V (good thing there aren't any common power sources with a voltage between 3.6 and 4.5V right? Well, yes, lithium batteries are common, but you don't use a battery to power something using an external clock; most of them

Note on resistor values

Early versions of this board used a 4.7k resistor. This is an excessive value, and is only compatible with jtag2updi programmers with a series resistor not more than 1k at absolute maximum. This was pointed out to me before SerialUPDI or the 2-series existed, Since then (spring 2020) I've been shipping boards with a more appropriate 470 ohm resistor, which can be bypassed entirely with a solder bridge jumper on the back.