Anarduino Mini

Arduino Uno.
Anarduino Mini

The Anarduino Mini has features similar to the Arduino Mini, but with a pad location underneath for an RFM73 2.4GHz module. It has no RAW input, and no regulator, so you have to supply 5V directly.

The Anarduino Mini is different. At first glance, it is just an Arduino Mini with no voltage regulator. It requires a regulated supply on Vcc. The RAW pin is not connected to anything. But there are pads on the bottom for attaching an RFM73 2.4GHz radio module. The board is 1/16" thick, where many other mini and micro boards are 1/32" thick, with a few notable exceptions, like the Deek-Robot Pro Mini.

Anarduino mini compared with an Arduino Mini.
Figure 1. Anarduino Mini compared to Arduino Pro Mini

A Mini is a Mini

The Arduino Mini is a mini Arduino. The Anarduino Mini is more like a life support system for an ATmega328. Would it be nice to find an ATmega328 with a clock, a reset button, and all of the filter capacitors - all the little bits that are a pain to gather and assemble? That is the Anarduino Mini. It doesn't even have a power LED (which we always remove). With no voltage regulator, you get to decide how to power it, and that is a good thing, because the first thing we want to do with these is make a data logger with RF capability, and that requires batteries.

After programming and reprogramming the Anarduino Mini while exploring the freedom from voltage regulation, we put the original bootloader back on and built a data logger. It runs at 5V, but that is because of the DS1307. It is currently out on the roof measuring it's battery and solar panel voltage, and logging them to a micro SD every ten minutes. It is drawing, generally, around 480uA from the battery, peaking at 50mA for 50mS out of every 10 minutes. We tried to use a common switching regulator, but the quiescent current of the regulator used more battery power than the entire data logger.

With no voltage regulator you can put whatever you want into it. Since the RFM73 modules have a maximum Vcc of 3.6V, the Anarduino should probably run at 3.3V. That brings up an interesting issue. A 16MHz clock frequency at 3.3V is out of spec for the ATmega328p. It should be running a clock frequency of no more than 13.333MHz. But this site has several boards which have dual regulators and are switchable between 5V and 3.3V. They are the InHaos Buono Uno R3 , InHaos BuonoLite Uno R3 , and the Freaduino Uno v1.8.1 boards. All three are Uno clones. Each has only a 16MHz crystal, and each works without any problems.

Anarduino Mini running at 2 volts.
Figure 2. Anarduino Mini running at 16MHz with a 2.0V supply

So being curious, we wired the Anarduino Mini to a variable voltage power supply and tested some things. Changing the fuses to turn the BOD off got the Anarduino Mini running perfectly at 2V. It even barely lit the LED with the blink sketch. The timers were right, and it would power up correctly every time. Programming was done with a 5V programming cable, which supplies the board with 5V as well. You probably shouldn't try programming the flash below 3.3V. Atmel doesn't recommend it, but then they recommend against running 16MHz at 1.94V, too, which is where things get weird. The outputs oscillate at a high frequency for about two seconds, then the ATmega328P ratchets. Power cycling with a 2V or higher supply fixes it.

It should be noted that these facts are not specific to the Anarduino Mini - it is the Anarduino Mini which caused us to dig deeper. The ATmega328P will exhibit this behavior, but with no other influences, like voltage regulators, at least the Anarduino Mini doesn't freak out before the ATmega328.

While it would be imprudent to advise anyone to run a 16MHz clocked device at 3.3V, we certainly won't have any problem with it ourselves, providing there isn't some other irritant, like extreme temperatures or electrical noise. This Anarduino Mini has turned out to be a great experience. The board is great, as are the people we've dealt with at Anarduino, and we look forward to what comes next from them.

P.S. This site does not normally endorse specific vendors, but is also the HopeRF distributor in the USA. Those little boards we have always trolled ebay looking for are most all there, and are shipped from the USA.

Anarduino Mini
MCU ATmega328
DigitalPins 14
Analog Inputs 8
Analog Outputs 0
Operating Voltage 5 / 3.3
Operating Frequency 16MHz
3.3V Output None
Test Current Draw14.4mA@5V 6.7mA@3.3V
Web Site Anarduino
  1. Information from manufacturers and other sources.
  2. Test current from sketch that exercises I2C, SPI, and analog pins.
Anarduino Mini pinout.
Figure 3. Anarduino Mini Pinout

The pinout of the Anarduino Mini is typical of the Arduino Pro Mini and Micro boards, with the exception of the placement of the A6 and A7 pins. We haven't seen others with the higher analog pins lined up like that.

There are additional pads on the bottom of the board that are specifically for the HopeRF RFM73-S modules.

While this site is about the Arduino and it's clones, deviants, knockoffs, and whatever else, we have to add that there is a USB to UART board available for the Mini, or anything else, which is as unique as the Anarduino Mini itself. The connector may be soldered in either of two directions, so the USB cable trails off the direction you prefer. And it has a 5V/3.3V switch on it. It is worth checking out.

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