This is a simple development board for the Atmel ATtiny841. It provides the familiar 6-pin FTDI header for connecting to serial and ISP header for programming via ISP, with DTR auto reset. This board is sold assembled, with all surface mount components soldered down, and chip bootloaded with Optiboot. Boards are sold in three versions - 16mhz, with crystal and 5v LDO regulator, and 8mhz w/out external crystal and either 5v or 3.3v LDO regulator. ENIG (gold) surface treatment for easy soldering on 0.063" FR4.

Using the core available from my Github at https://github.com/SpenceKonde/arduino-tiny-841 the ATtiny841 can be used with the Arduino IDE, with optiboot bootloader support.

What sets this apart from a typical ATtiny841 breakout board or generic SOIC-14 breakout board is that it provides the appropriate header for serial programming of an ATtiny841, and the chip comes pre-programmed with the Optiboot bootloader, so programming it with the Arduino IDE is as simple as using an Arduino Pro Mini (You can always erase the bootloader by programming via the ISP header if you need the space and/or wish to program using Atmel Studio instead of Arduino). As of 11/16/2018, these are preloaded with a new version of Optiboot (from ATTinyCore 1.2.1) which does not interfere with using the WDT as an interrupt source - the largely-unused EE_RDY vector is used for virtual-boot instead.

The ATtiny841 - a remarkable step up from the 84

The ATtiny841 is pin compatible with the classic ATtiny84, however, it has a greatly improved suite of peripherals. In addition to the dual hardware serial - by far the most exciting feature - it has full master/slave SPI (not a USI), and a second 16-bit timer, allowing 6 PWM outputs. The analog input capabilities are also greatly enhanced, with dual on-chip analog comparators, analog input on every pin, and almost every imaginable combination of pins available as a differential pair, with gain of 1x, 20x or 100x - few AVRs have a more capable ADC!

This board is sold ASSEMBLED but WITHOUT PIN HEADER - Bare boards available here

Features

• 12 single-ended ADC channels (one on every IO pin, including reset)
• 10 differential ADC channels in 46 combinations, with programmable gain (1x/20x/100x)
• 2 Hardware UARTs
• 3 independent timers, 2 of which are 16 bit (same features as timer1 on the ATmega328p), each with two PWM channels (ie, SIX PWM CHANNELS).
• Hardware SPI
• Dual on-chip analog comparators
• Internal oscillator factory calibrated to within 2% - good enough for serial at 8mhz w/out crystal, provided it is run at 3.3v (the oscillator frequency increases significantly above 4v).
• Assembled in USA.

Auto Reset

This board has the standard Arduino-style DTR autoreset circuit: The DTR pin of the serial header is connected, through a 0.1uF capacitor, to the reset pin, so that when the serial port is opened (whether to upload code or connect a serial monitor tool), the chip will reset. This can be disabled by cutting the trace marked RST_EN - if this is done, a 2 pin 0.1" pin header can be installed in the adjacent holes, and bridged with a jumper to temporarily re-enable it.

Pin header required (optional):

• 1 piece 2x3 0.1" pin header (for ISP programming)
• 2 piece 1x9 0.1" pin header (3 each are power/ground rest are I/O)
• 1 piece 1x6 0.1" pin header, recommend 90 deg angled (for FTDI header)
• 1 external power connector on 0.1" centers (pin header or something like KK-100)
• 1 piece 1x2 0.1" pin header for RST_EN jumper (not needed on new version, unless you cut the trace)

Optional Colored Pin Header

An extra cost option for colored pin header kits is now available - this is standard 0.1" pitch square pin header in bright colors for an instant reminder of which pins are for which purposes (it also looks damned cool!): - 1 piece each 1x3 red and green, for Vcc and Ground pins on the two sides - 2 piece 1x6 black - 1 piece 1x6 yellow 90-degree angle, for the "FTDI" style serial header - 1 piece 2x3 white, for the ISP programming header

Optional Serial Adapter

A CH340G-based serial adapter is available as an option. This will be supplied with a 6-pin cable as shown. These are mass production adapters, however they are a cut above the most common units, and have a switch to select 3.3v or 5v operation. They break out the pins necessary for programming one of these breakout boards, or an Arduino Pro Mini or similar - Vcc, Gnd, TX, RX, DTR and CTS.

Custom options

Custom options are available for regulator and crystal - specify in order comments what regulator voltage and crystal you want. Note that at voltages above 4-4.5V, the internal oscillator runs too fast for UART communication, so the bootloader will not work and this configuration is not recommended. If you want a chip set to use the internal oscillator, and >3.3v regulator, please acknowledge that you are aware of this issue in the order comments (else I will contact you to confirm, which could delay your order).

Available custom speeds are internal 1mhz or 8mhz, or external 7.3728, 8, 9.216, 11.0592, 12, 13.56, 14.318, 14.745, 16, 18.432, and 20mhz, and operating voltages of 1.8, 2.5, or 3.3v or 5v. Please refer to fig 25-27 on pg 248 of the datasheet for max rated clock speed at a given voltage - if you are requesting a crystal which is faster than the manufacturer spec for the regulator voltage, please acknowledge in order comments that you know that you're asking for a board that is outside manufacturer spec (otherwise I will contact to confirm, which could delay your order).

Please allow 1-3 days extra processing time for all custom orders.