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Description: It's blue! It's thin! It's the Arduino Pro Mini! SparkFun's minimal design approach to Arduino. This is a 5V Arduino running the 16MHz bootloader. Arduino Pro Mini does not come with connectors populated so that you can solder in any connector or wire with any orientation you need. We recommend first time Arduino users start with the Uno R3. It's a great board that will get you up and running quickly. The Arduino Pro series is meant for users that understand the limitations of system voltage (5V), lack of connectors, and USB off board.

We really wanted to minimize the cost of an Arduino. In order to accomplish this we used all SMD components, made it two layer, etc. This board connects directly to the FTDI Basic Breakout board and supports auto-reset. The Arduino Pro Mini also works with the FTDI cable but the FTDI cable does not bring out the DTR pin so the auto-reset feature will not work. There is a voltage regulator on board so it can accept voltage up to 12VDC. If you're supplying unregulated power to the board, be sure to connect to the "RAW" pin on not VCC.

The latest and greatest version of this board breaks out the ADC6 and ADC7 pins as well as adds footprints for optional I2C pull-up resistors! We also took the opportunity to slap it with the OSHW logo.

Note: A portion of this sale is given back to Arduino LLC to help fund continued development of new tools and new IDE features.

Dimensions: 0.7x1.3" (18x33mm)


  • ATmega328 running at 16MHz with external resonator (0.5% tolerance)
  • 0.8mm Thin PCB
  • USB connection off board
  • Supports auto-reset
  • 5V regulator
  • Max 150mA output
  • Over current protected
  • Weighs less than 2 grams!
  • DC input 5V up to 12V
  • On board Power and Status LEDs
  • Analog Pins: 8
  • Digital I/Os: 14


Replaces: DEV-09218

Comments 137 comments

  • I know you’ve only just updated these boards, but may I make a suggestion for the next version?

    For my battery-powered projects I’ve been modifying my ProMini boards by cutting the trace from the voltage regulator. See this picture. This reduces the minimum current draw from ~1mA to ~1uA in power-saving modes.

    It would be really nice if the next PCB revision had this connection on solder-pads. That would make the low-power modification easier to do (and undo).

    • That’s awesome - I second this.

    • what is the voltage of your battery,3.7v? Are you connecting the battery to Vcc or VRAW? Are you also cutting off the status led? After cutting the trace, are you driving the Pro mini with 3.7v? is everything working fine under this voltage without regulation?

      • In various projects I use a 1.5V battery boosted to either 3.3V or 5V, depending on whether I’m using an 8MHz or 16MHz Arduino and what voltage the other parts of the project require. The trace-cut disconnects the regulator and the power LED, so you need to provide power to Vcc.

    • Can you let us know what connection you’re severing on the schematic when you do this mod? We’ve been using a lot of these boards for a project, and would love to reduce the standby current.

    • That trace disconnects the 5V regulator, and it’s output 10uF cap, the VCC pin of the FTDI header and the power status LED. from the rest of the circuit. You will not be able to reprogram your circuit without powering the unit from batteries directly on the Arduino’s VCC header pin. You’ve also lost some of your 5V stiffening/decoupling… not too bad if you are not doing anything noisy with the circuit, especially since you are running on batteries. However, I think just providing a solder jumper for the power status LED is the thing that will really matter for current draw. (5V - 2V) / 10k = 0.3mA assuming it’s a red led. I can’t imagine there is much current back-feeding into the 5V regulator, but you’d have to check.

      • The reg pulls about 0.7mA. Otherwise I’d have just cut the LED, for the reasons you list. The cut can be undone by connecting the two Vcc pins together.

  • Do you know when you are going to have more of these available?

  • I recently bought several of these, and they work really well. I don’t use my Arduino Uno any more because this is less expensive, and is smaller. The only thing I didn’t like is that it needs an FTDI board/cable.

    • Have you considered the Pro Micro - 5V/16MHz? It’s pretty close to the Mini, except that it uses an atmega with USB support on-board - so you don’t need the separate FTDI. Of course if you manage a bunch of Minis with a single FTDI, then that is more economical.

      • fyi - the the bootloader on the Miro takes almost 5 sec to bootup due to usb device (keyboard/mouse) emulation. pain in the butt when u are trouble shooting code and need to reset the board often.

  • I have this hooked up to an ID-20 for an RFID project but it doesn’t seem to be receiving data correctly. The sketch uploads correctly and everything looks fine until I scan a card and then nothing happens. I prototyped everything out on a breadboard UNO and it works fine if I plug everything up to it but not when I use the mini.

    I am following this build:

    Is there anyway to test the serial pin (RX) ?

    • The best way to make sure the serial port is still working is to write a program where the Arduino echoes all serial commands it receives. Then, you can hook it up to a computer, send random characters to it, and watch them appear in the serial monitor.

  • Does the Mini Pro have power management features that allow me to hard-wire 5V power to the board, and then still plug in an FTDI board that is powered via USB? Or do I need to disconnect the board power before plugging in the FTDI?

    • it works with power supply connected though you risk damaging your usb port if your power supply spikes above 5vdc..

    • There is no power management. If you are powering the board directly from the arduino’s VCC pin, you should probably disconnect that power source when plugging in your FTDI cable.

    • Also wondering this.

  • Holy crap SF! You helped me solve another engineering problem. I needed a small Arduino/Micro powered off of 12VDC prepacked. This fits the bill. Thanks!

  • I plugged my regulated 5v power supply into a jack, then ran the +/– to my 5v Pro Mini’s VCC and GND. I really should have checked the polarity of the jack, but I didn’t and it was opposite of what I assumed. I plugged it in and the thing literally burst into flame. Does “Reverse Polarity Protected” not mean what I think it means?

    • Sorry about that (it happens to the best of us), but from the description and schematic I don’t believe these are reverse-polarity protected - if you let us know where you see that stated I’ll be sure to have it removed.

      EDIT: I’ll add that there’s no practical way I know of to reverse-polarity protect the VCC line, since people will use it for both a power input and a power output. A diode would necessarily be one or the other.

      • Put a diode from Vcc to ground, instead of inline. Although, that only works if the Vcc feed has a fuse, or the diode can handle more current than the supply can source. Perhaps a small resettable fuse between the connector and the diode.

  • I just got one of these, and I can’t upload anything. I get “programmer not responding”. I’ve installed the latest FTDI USB drivers, and uploading works with another Pro Mini (from a Protosnap). Could the bootloader be corrupted?

  • I have grown to appreciate this little board for its size and capacity. The ability to strap on sensors and then I2C them back for post processing or data collection is making my current and planned projects more economical and tractable. Nice one Sparkfun!

  • Should the board come with the pins?

    • 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.

  • Do the pins supply 5v in output mode?

    • 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.

  • Got this on sale for $3. O YAH!!!!

  • Is it possible to program one of these with a prop-plug? I just don’t want to buy a breakout board if I already have the hardware…

  • Does this board need anything done to it so it doesn’t reset randomly? I don’t have one, I might get one, but I don’t want to have this problem.

    This is what I found:

    “-Reset. Whenever this pin is connected to ground, the Arduino Mini resets. You can wire it to a pushbutton, or connect it to +5V to prevent the Arduino Mini from resetting (except when it loses power). If you leave the reset pin unconnected, the Arduino Mini will reset randomly. ”

    • 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.

  • Can this board be used to program an ATtiny85 ?

  • Hi, I’m a software guy, so please go easy on me! I need to drive 4 9v devices (in current sinking mode) that draw close to 20ma each with a Pro Mini. I know this is very close to the limit on the outputs. I need a simple circuit that will get this done.

    • 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.

  • I have one of these running when powered via FTDI Basic but when I try to power it from a 6V, 9V, or 12V wall wart my sketch won’t run; I only have a red LED on the header side of the microprocessor. That LED is lit when powered by FTDI Basic but it is much brighter with a DC adapter to VCC. Any thoughts?

    • Solved by Arduino forum user: tap power to RAW and the sketch runs correctly. VCC on the side of the Pro Mini is the output side of the voltage regulator.

  • System resets resulting from a Watchdog timer (wdt.h) are not supported by the bootloader. when the watchdog timer triggers a reset, it will reset the chip but will not reset the timer therefore it will continuously reset every time the chip boots up. This essentially bricks the arduino unless you catch the the chip during the bootloader sequence with a sketch upload.

    • Hi Dave - sounds like you are fighting the good fight against I2C! It’s a tricky one. You are correct that a soft reset may not reset a watch dog timer but I don’t believe it to be true for a power cycle reset. WDT is reset with a power up so you should be able to reflash your board with a power cycle.

      I’ve never bricked an Arduino after bootloading. It’s usually when I fiddle with fuse bits, with an external programmer and no external osc that I get into interesting brick-possible situations.

  • I fried one of the c106 caps on the board, is my board shot? or is it usable and what will the absence of this cap cause?

  • These are great, but I hate having to solder on the row of pins to get a reliable connection to the FTDI breakout, for the very temporary task of programming. To get around this, I glued together a bunch of pogo pins and made a little adapter which makes it really easy to get a nice solid connection for programming a bare Pro Mini.

    I’m sure SparkFun could come up with a much more professional-looking spring-loaded adapter, though. Maybe even with a clip or something to hold things together?

  • I am planning to switch out a couple of Uno boards with these Pro Mini 328 - 5V/16MHz. Just want to make sure that the I2C can communicate between Uno and Pro Mini-5V without a level shifter ?

  • For those of us stuck on Eagle 5.x, does anyone have an engineering drawing or something equivalent for this board? It seems to use 0.1" pitch headers. How far from the center of these pins to the board edges? Is the programming header centered on the short dimension, and how from from the edge? The coordinates of A4 - A7 would be great too. Thanks. - Brent

    • Try the Eagle files from the previous version. Note that this board does add 2 more pads (A6 and A7) in the middle of the board, similar to A4 and A5 which were also present on the older board. Just to answer your specific questions: Yes, 0.1" pitch headers. Distance from center of pads to edge of board is approximately 0.05" (approximate because there’s always a chance of a tiny bit difference in board cutting). The programming header is indeed centered on the short side, from the center of its pins is also 0.05" away from the board edge.

  • So I take it that digital pins 0 and 1 are available under TX and RX pins, just not labeled? I know you’re not supposed to use 1 or 0 as a GPIO but still I need them… BTW GREAT board.

    • 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.

  • Hello, I was wondering what values will have the I2c pull-up resistors for this model?

    • 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.

    • “… has an internal pull-up resistor (disconnected by default) of 20-50 kOhms” -

  • Which bootloader is this running? Looking in hardware/arduino/boards.txt in my Arduino 1.0.5 app I see pro5v328.bootloader.file=ATmegaBOOT_168_atmega328.hex. Is that correct? Could I use optiboot on this instead?

    • It’s a bit confusing but the Pro and Pro Mini boards have been running an Optiboot equivalent (Arduino used Optiboot and modified it a bit) for a number of years. If you need the exact date we started shipping with Optiboot-esk bootloaders I may be able to dig it up.

      • Hmmm… something fishy is going on. wc -c hardware/arduino/bootloaders/atmega/ATmegaBOOT_168_atmega328.hex gives me 5533. However wc -c hardware/arduino/bootloaders/optiboot/optiboot_atmega328.hex gives me 1467, which is 3.7 times smaller. (Yeah I know that’s not really the way to measure the bootloader size on device.)

      • No worries. I was just wondering what the Pro Mini I got for Christmas had running, and whether I could squeeze out some more RAM or boot time by going to optiboot.

  • What voltage regulator is used on this board? Based on the specifications the on-board voltage regulator looks like it is a linear regulator, not a switching regulator. Is this correct?

  • I seem to be having a problem with my board resting every couple of seconds. I have tried soldering 120 Ohm equivalent resistance between vcc and the RST as well as a 10 micro-farad capacitor between RST and GND. Aside from removing R2 and C2 I don’t know where to go. Is that a good option? Will the Sparkfun FTDI programmer be able auto-reset? It’s not a super big deal if I can’t auto reset because where this is going it will not be removed for a long, long time.

    • 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?

      • Thanks for the reply, I figured it out. The LED strip I was running was being powered from the board, so it was drawing way too much current, causing the board to overload and shut down.

  • what pin do you use for I2C on the pro mini?

  • What pins are used for I2C communication? There are 2 extra analog pins, do you still use A4 and A5?

    • Just a heads up, I’ve been fighting with the Wire.h library for the past month. To be quite honest, there are a lot of bugs in the official version of the Wire library and in the end I’ve had to use 2 different modified versions of the TWI.c that steamed from this forum:

      I managed to get a working version of the library with a modified the twi.c file for the master devices only with timeouts and a bus reinitialize inserted into the “never ending” while loops.

      The original version of the file with timeouts works best for slave devices.

      High data traffic is also a major problem. the communications i was using was fairly simple. i used one byte of data to one device per scan cycle of the arduino. If you try to communicate with multiple devices within a single scan cycle the system will freeze.

      also with any noise on the vcc line the reliability drops significantly.

      I would love to see someone fix this issue. Sadly the problem is outside of my skill level. Its quite frustrating.

    • A4 and A5 are SDA and SCL respectively. On the Pro Mini these are the two inner pins (look at the bottom of the board).

  • Just a note to those that need to use RX1 and TX0 as digital outputs or inputs. This may be common knowledge, but i just discovered that if use TX0 you must call it digital pin 1 (one) in your program, and if you use RX1 as a digital output, you must call it digital pin 0 (zero) in your program. You also need to remove any serial commands from your program, as you can not use these as digital out puts and for Rx and TX also. the pins on the broad are like this: 9 8 7 6 5 4 3 2 Gnd Rst 0 1

    BTW, this a great product.

  • How many Pro Mini 328s are sold annually?

    • We sell these in the tens of thousands when you include both this and the 3.3V versions. They are pretty popular. :)

    • A lot. For this particular model - since I don’t think sales numbers would be officially reported - I’d have to guess by snapshots of inventory that this year, so far, at least 3,000 were sold - possibly 4,000 - and that’s not counting all the ones they’ll sell this month (you can see they’re planning on producing another 720 as it is). Note that there’s a huge margin of error in these numbers as doesn’t have a day-by-day snapshot :)

  • I have just purchased a Pro Min 5V/16Mhz and an FTDI 5V cable from Sparkfun. I have updated the FTDI driver on my Windows 7 computer and loaded the latest V1.0.5 Arduino software. I load the blink program, sent the com port and the board appropriately and download. The green LED on the Pro Min flashs about 4 times, then waits about 4-5 seconds and flashes 1 more time. I then get an error “avrdude: stk500_getsync(): not in sync: resp0x00” in the programmer.

    This is the first time that I have purchased something from Sparkfun. I would have thought purchasing Sparkfun products that they would work.

    Can anyone advise how I can fix this problem.

    • If you use the FTDI breakout board instead you can get it to work by NOT setting the processor to the 5V Pro Mini 16MHZ mega328 option. Use the 3.3 V Pro Mini 8 MHz mega328 option, as the FTDI breakout board runs on 3.3V. I had your problem exactly until I realized the processor needed it to be seen as 3.3 V. Further experimentation revealed trouble with loading large files. I’m using Windows 7, so I also checked for serial port settings. In my case it was COM12. I set the baud rate to 57600, enabled hardware handshaking. Finally I changed the programmer setting to ‘use Arduino as ISP’ and then it didn’t have problems with loading files bigger than the blink sketch. So far so good, I think that will make it work properly, good luck.

    • did you try selecting the appropriate board from “Tools>Board” option in Arduino software?

  • What is the tolerance on the ftdi vcc pin? Im using a 5v wall wart (SFE) to power the project & it appears to be outputting around 5.5 v Would prefer not to use the raw pin if possible…

    • According to the datasheet, the VCC pin of the FT232R used on the ftdi breakout can take up to 6V (absolute max rating). However, VCCio is listed as max 5.25V - and if you connect the breakout board to the pro mini, VCCio is tied to VCC.

      That said.. I suspect the max 5.25V is listed due to USB compatibility, and your 5V wall wart’s voltage may well drop when under load bringing that 5.5V down anyway.

      That said… it’s probably still a good idea to go through the on-board regulator. Any particular reason why you would prefer not to?

      • @Kamaqasi - thanks for the quick reply… I’m trying to re-utilize the FTDI headers to power the pro-mini due to circuit board real-estate issues.

        I’m unable to locate a schematic that specify’s the tolerance level for the VCC pin(s) on the pro-mini - or that illustrates the relationship (if any) between the FTDI header RX0 and TX1 connections and the RX and TX connections on the port side of the circuit board.

        I only need VCC; GND;RX and Pin 12 for my project - was hoping I could use the same FTDI connections that are used to program the board - with the regulated 5.0v Wall Wart connected to the FTDI Header VCC / GND pins.

        Would you know if the RX/TX connections in the FTDI header are connected to the RX/TX connections on the side of the pro-mini?

        Thanks again for your help…

  • What would I need if I wanted to attach a battery and the ability to charge that battery over the same usb connection that i use for programming it?

    Would this component work?

  • I have one of the 5V boards, when I supply 9V (from battery) on RAW, I see 9v on the VCC connection, I thought this was supposed to be regulated to 5V?

    • Sounds like you have a short across the Reg. Check for any soldering shorts - more likely you have shorted something or done something wrong, rather than SF not testing it correctly. If you really have 9V on Vcc, I don’t think the Micro is going to be too healthy now! If you’ve checked and you’re sure it’s not you, then contact customer service.

  • What’s the crystal on these? Anyone have a part # for it?

  • okay now for the $64,000 question……

    WHY wasn’t this NOT put on a 28 pin DIP format instead of the 24 pin DIP format? This should be considered on the following batches so that those 4 extra pads that are in the WIERD places can be properly addressed….

    • The answer is probably the same answer to the question “Why don’t they fix the Arduino pinout up?” - For whatever reason, they tend to stick with a dud format to keep compatibility, even though the design could be made much better, hence future generations will be stuck with that until somebody brings out something in a decent footprint that becomes more popular than whatever came before it.

    • My guess is that they wanted to follow the now somewhat conventional footprint/pinout that the 24-pin Basic Stamp2’s use. Particularly, pins 21 through 24 have the same functions, providing the same necessary power supply, ground, Vout, and reset lines the Basic Stamp2 uses. I also noticed the new 24-Pin version of Parallax’s Propeller microcontroller uses the same pinout.

      The programming connections are different, but that is to be expected in this case.

      I have several older BS2-based projects that I am considering reworking and “supercharging” with this new Arduino board. The hardware compatibility will allow me to resurrect some of those older projects and try some things that the BS2 is simply to slow to handle.


  • could anyone tell me the operating temperature range for this board?

  • it weighs 1,53g no-headers and with 3.67g with headers

  • The FTDI cable does not bring out DTR but does bring out RTS. I read a lot of stuff about this, some claiming that DTR is necessary for reset and other claiming that RTS will also achieve reset. I breadboarded a programmer using RTS and successfully downloaded my sketch into an Uno preloaded with the bootloader.

  • I highly recommend buying a 3.3 volt regulator with these guys, just in case.

    • ?

      • I guess that wasn’t a very well articulated comment. People buying this board who are used to the Arduino having a 3.3v out might be surprised to find this board without one, if they don’t read the description thoroughly.

        • Fair enough. Note that we also carry a 3.3V version, which I find very useful (it will happily run off a 3.7V Lipo, and will talk to 3.3V sensors with no voltage-translation circuitry required).

  • I noticed there is a green LED on the Pro Mini connected to the SCK line (digital pin D13). I’m using SPI to talk to a digital pot, which uses SCK. I’d like to move my project from a bare 328 to the Pro Mini. Will the Pro Mini’s LED interfere with SPI? Thank you in advance!

    • On most arduinos, like the UNO, there is an led there that doesn’t seem to interfere with any SPI devices I’ve used.

  • What type of “Over current protected” is there on this board?

  • How much power does the CPU use? The page says each pin can sink 40ma. Looks like the regulator can deliver 150 ma.

  • Anyone have the correct timer and pin settings for AltSoftSerial for the 5V board?

  • is this compatible with voltage divider shield found here: ?

  • I inadvertantly purchased some of these boards for my sensor project instead of the 3.3v version. Does anyone know if its possible to burn a custom bootloader which changes the CPU pre scaler, or to use the internal oscillator to get the clock speed down to 8mhz or lower. Also if we bypass the voltage regulator would that be enough to run this off of 3.3v? What other changes would be necessary? changing the fuses, etc?

    • The only differences between the two boards are the voltage regulator and the external oscillator (sorry, and the bootloader). The ATmega itself will happily run at either 5V or 3.3V.

      If you have a 3.3V supply, you can certainly feed that into VCC and run the board at 3.3V. Which leaves the 16MHz oscillator. One option at this point is to keep running it at 16MHz (and choose “5V/16MHz” in your IDE so the timing is right). Although this is technically outside the guaranteed safe envelope, these chips tend to have a bit of margin built into them to tolerate manufacturing variations. It may work perfectly fine.

      You’re correct about the rest of your options; if you must run at 8MHz, you can use the internal 8MHz source (requires new fuse bits) or divide the external source using the prescaler (requires changing a register). You -might- be able to get around this without making bootloader changes, but it would be hacky - you’d have to compile your code for 8MHz (including changing the prescaler register early on), but the bootloader would be running at 16MHz. Let us know what you end up doing.

      (And it should be said - if you haven’t used the boards yet, you can always contact our customer service department for an exchange). Good luck!

      • Thanks! Yes, I did in fact burn new fuse values and then a new bootloader to run at 8MHz and fed in 3.3V on VCC, everything runs like a charm. It still seems to draw a bit more power than I’d like in sleep mode and probably going to try to cut the trace to the voltage regulator.

  • I have Pro Mini. On the back side it have checked 3.3V and 16Mhz by black pen.

    What type Pro Mini have I got ( 3.3 or 5V)? How can I check it?



    • That’s definitely strange, since that isn’t a combination we manufacture! Very sorry about that. If you put 6V onto the VIN pin, either 3.3V or 5V will appear on the VCC pins. If the part wasn’t what you were expecting, or you have any trouble with it, please contact our Customer Support department and we’ll make sure you get a new one (with the correct labels!)

  • is there already an eagle library with a footprint of this? i want to make a schematic that integrates this board but would want to reinvent the wheel if someone else already did it

    • It’s in the Sparkfun Eagle Libraries, in “SparkFun-Boards.lbr” as “ARDUINO_MINI”

      • Unfortunately it looks like the Sparkfun Eagle Libraries' “SparkFun-Boards.lbr” is for the older version, ie without A4, A5, A6, and A7. So if you want to use those pins, or if you want to use i2c, you need to put in your own off grid headers. It would be nice if Sparkfun can update the library. one entry for the vanilla mini and another for the Pro mini

        • That’s a fair request; I’ll get an updated version in there. Thanks for the feedback!

          • Has this been updated? I think I have the newest version of the library but it doesn’t look like they’ve been added.

            • We just added in the Pro Minis about a week ago. Try updating your library from the GitHub repo.

              • Thanks!! So if I have some previous boards designed with the old Pro Mini part will they get messed up if I replace the library with the new one since the new Pro Mini part has additional pins?

                • This is a possibility. If you have a lot of boards based around the old design, I’d recommend copying the old part into the new library once you have it downloaded. Or just keep the old version of the library and change the name on one of them. At that point, it just comes down to what organization method works for you.

  • I’m having a straaaange issue with this board. Strange indeed, yes.

    I moved to this board from an Uno. The circuit it’s interfacing with remains essentially unchained.

    Part of said circuit is a little Piezo Buzzer. It produces the occasional beep. Which with the uno always sounded fine.

    The buzzer now sounds like it has a sore throat when powered from my 9 or 12 volt wall warts. (through the raw input). Strangely enough, it sounds just fine when powered over USB or directly by my benchtop variable power supply (spanning the 5-12v range).

    Any thoughts as to why? I probed the buzzed with a little oscilloscope and couldn’t detect a marked difference in the readings.

    • I had a similar problem with something that worked fine when powered from my benchtop power supply, but sounded weird when powered from a wall wart. Apparently my wall wart was too wimpy to keep up with sudden changes in current. I fixed it by adding a big capacitor – 1000 uF – across V_RAW and GND.

  • Does anyone know how many timers these have?

  • Has anyone found like a proto shield for this form factor. Yes I know about the one here but it really doesn’t fit my needs. Personally I don’t see it fitting anyone’s needs but thats another thread. :-)

    My plan is to make a LED Controller board that uses a Darlington Driver 8-Channel ULN2803 that would control the LEDs, either singles or strands, through JST 2 connectors.

    I would have a few inputs as well also using JST connectors.

    So the 2803, some JST’s and probably LEDs on the board for status of the strings for trouble shooting. I got some really tiny 1.8 mm LEDs from Evil Mad Scientist for that.

    I want it to be very generic/flexible so it could be used for a number of control projects but it mostly for costumes hence the use of a pro mini.

    • Any meaningful reply would have to be based on why you believe the ProtoShield for Arduino Pro Mini does not fit your needs. You’re correct that this would be another thread, so perhaps you can explain in that product’s comments?

      But here’s a less meaningful reply in the mean time: Why not pick up a generic protoboard? Unlike the main Arduinos with their spacing issues (solved by a product that should never have had to exist, the Arduino Offset Header, all of the pins on the Pro Mini are on a standard 0.1" grid. Just cut the board down to the size you want/need.

      • I just don’t see what you could use the protoshield for since it doesn’t bring up the I/O pins. If you read the comments its already been requested to add all the pins so no need for me to add a ‘me too’. I brought it up since I figured someone would point me there.

        But anyway, forget the second part because I don’t know how I never found this. Mini FET Shield

        Its pretty much EXACTLY what I need. Oddly I never found it here. I found it by searching for mini shields at

  • Is anyone having issues with programming these using the ftdi basic usb to rs232? I seem to be having a timing issue where it seems to reset as it is supposed to and all the right lights flash like the board is OK but… I get ‘stk500_recv() programmer is not responding’ errors. I have soldered and resoldered. I looped the ftdi basic and verified that it works. I re-checked everything twice. I’ve tried every conceivable combination of baud rate. I even removed the DTR and tried to manually time the reset like a crazed lunatic hitting the button and trying to “catch” the timing by hand.

    I came across this: from over a year ago and am wondering if replacing the bootloader is my huckleberry or if this is from a previous revision only?

  • Does this thing have the Analog reference pin out? Or am I missing it somewhere?

    • Not missing it - ARef (pin20) connects to C1 connects to GND. Analog pins should thus be relative to the 5V Vcc. You could wire something to it if you need a separate ARef - if you’re adventurous enough.

  • I protyped a project on an uno, then bought a pro mini from sparkfun (the 5v/16mhz version), then flashed the same project onto it, and it runs very slow. Like half as fast at least. Is there any reason a project that runs quickly on an uno would run slower on this, even though it’s supposedly the same clock speed as the uno? (or is mine broken and running at 8mhz?)

  • I’ve run across some unusual quirks when using this board. I’ve used this board as a controller for an EM-38A (the latter set to Binary trigger mode) so that I could read 13 digital inputs and put out what is essentially a byte address via the analog pins.

    Is there any reason why A6 and A7 can’t seem to write a digital HIGH or LOW? Does that have to do with the board, or is that a limitation in the ATmega328? Turns out I could wire around that problem, but still I was surprised to encounter it.

    I also had issues with Pin 1. I set it as input and pulled it up with a HIGH write, but it never reads LOW even when it’s closed to ground. I thought that one could use pins 0 and 1 as normal pins long as one isn’t worried about serial communications during normal operation – am I wrong about that?

    I knew I was running up against the upper limits of pins. (I’d forgotten that on most standard boards pin 13 is loaded down with an LED). I’m starting to wish I preemptively bought a multiplexer for this project, just to be on the safe side.

    • Pin A6 & A7 are pure analog input pins.

      • Would be good if they specifically noted this on the circuit diagram, though they don’t show it as PC6/PC7, so I guess it ‘implies’ that. @C Poff, did you ever get Pin 1 sorted?

  • How hard is it to interface this board with the WiFly module( I don’t see any SCK MISO MOSI pins so I’m confused how the SPI would work. (I’m new to all this. Please do explain more if my question does not make any sense)

    • Take a look at the hardware page on the website,

      SPI communications are done on pins 11 (MOSI), 12 (MISO), 13 (SCK).

      Also, look at the SPI library page,

  • ok how would i go about programing this, i dont have much time to order the FTDI breakout. I have an arduino mega 1280. is there code out there that i can upload onto my arduino mega, that would allow it to be the FTDI?

    i know all i need is Tx,Rx,5v,gnd, CTS,RTS. but how can i get thoes out of the arduino mega 1280?

  • I am a relatively new Arduino user - have been playing for about a year now, but have only done a handful of small projects. I’ve recently purchased this 5v pro mini and a triple access accelerometer ( The accelerometer is a 3.3v piece, and this pro mini is a 5v. If I want to use the two together do I need to get a 3.3->5v logic controller (for example or can I simply build myself a circuit that has a 3.3v power source? I was planning to design this into a project that would have a custom PCB, and if I can simply plan in a 3.3v regulator, I may do that.

    Happy to supply more details if more info is needed.

  • After laying out a board for the previous revision of the Pro Mini I thought it would be nice to get all those other pins beyond the dip pattern into the Eagle footprint. I used flying leads for DTS, SDA and SCL to connect onto the PC board. Nobody would be forced to put header pins into the non standard locations, but it wouldn’t really be difficult either.

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