Member Since: June 4, 2013

Country: United States


Electrical Engineer

  • Since many people just solder wires to the connections, they don't need to get pins. Adding pins to the package would add to the cost. If you need pins, you could use these.

  • You can use those pins as GPIO when your sketch is running so long as you recognize that they will be set up as serial I/O during the initial bootloader period after reset. That means the TXO pin will be set up as an output with a high value by default, and the RXI pin will be in input mode with the internal 20-50K ohm pull-up resistor connected. If your projects use of the RXI pin causes it to change from the high state during the bootloader period, the bootloader will likely interpret that as a command from a programmer and attempt to interpret it. An unfortunate sequence of state changes on the RXI pin could keep the Pro-Mini in bootloader mode and your sketch would not run.

  • The internal pull-up 20-50K ohm resistors in the Atmega 328 microprocessor can be used if you have very short lines with very low capacitance and use a low bit rate. However, typically you will need a smaller resistance value to get good operability. I typically use 3.3K ohms, and if you use the 0603 size surface mount resistors, they can be soldered to the available pads on the back of the Pro-Mini. The Pro-Mini doesn't come with those resistors by default because the pins can also be used for analog input and in that case, you wouldn't want to have the pull-up resistors.

  • The board already has a pull-up resistor that is sufficient to keep it from externally resetting unless the reset pin is actively grounded. Some things to look for: Is anything connected to the reset pin that can pull it to a low level? Does your sketch do anything that might activate the watch-dog timer and then let it time out after a couple of seconds? Does your sketch contain any recursive function calls that may get into an infinite recursion state?

  • A good way to do this is using a 2n2222 transistor and a 3300 ohm resistor for each driver. Connect one side of the resistor to the digital output pin, and the other side to the base of the 2n2222. connect the emitter of the 2n2222 to ground, and the collector to the low side of your device. Connect the high side of the device to 9 volts. When you send a high to the digital output pin, the device will turn on, and when you send a low, it will turn off. You can pick up the transistors and resistors at Radio Shack, or order them on-line from Sparkfun, Digi-key or a number of other places. Sparkfun doesn't sell the 3300 ohm resistor by itself, but that value (3.3K ohm) is in their resistor kit.

  • If your supply at the RAW pin can handle it, you can use up to about 250 milliamps of current at 5 volts from the VCC pins. The actual current available is dependent on the currents that must be sourced from the other outputs on the Pro Mini module. For instance, if you use six of the digital outputs, and each of them must source 20 milliamps of current for your project, then there will only be (250 - 6*20) or 130 milliamps available at the VCC connection.

  • The Arduino Mini that you have referenced, and the Arduino Pro Mini sold here are two different devices. The Pro Mini has a 10K ohm pull-up resistor to VCC internally on the RESET line, so it must be actively driven to ground to cause a reset to occur.

  • Is there a Linux version of the software? Without that, the scope wouldn't be worth much to me.

  • After playing around with the Sparkfun Addon files a little more, I think I have found a better solution than using the symbolic link. If I edit the ~/sketchbook/hardware/SF32u4_boards-master/boards.txt file to replace the line:

    with the line:

    then the build will use the default Arduino IDE cores folder instead of the one from Sparkfun. The advantage of this approach is that it is no longer required for the user to know where the default IDE cores folder is located, and if it changes this change will hopefully automatically find the new location. Also, this method will likely work under Windows as well as Linux.

    I suspect that the other board types should be changed as well, i. e.:



  • I tried using the Pro Micro with the Arduino IDE version 1.0.4, and could not get my sketch to compile correctly. After looking through the IDE source code and the Sparkfun Addon Files, I found that for IDE versions later than 1.0.2, it is best to replace the ~/sketchbook/hardware/SF32u4_boards-master/cores folder with a symbolic link to the real arduino cores folder. On my Debian Linux system that is at


    After making that change, my sketch built correctly, and worked just as it had on the Arduino Uno where it has been used in the past.

    It appears that some of the changes for IDE version 1.0.2 made the IDE cores folder compatible with the Sparkfun version. After version 1.0.2, other changes in the IDE have made the Sparkfun version incompatible with the rest of the Arduino IDE.

    Has any one else had problems getting the Pro Micro to work with IDE version 1.0.3, 1.0.4, or 1.0.5?

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