Arduino Pro 328 - 5V/16MHz

Replacement:DEV-10915. The new version of this board uses a sturdier right angle switch and eliminates the overhang for the FTDI header. This page is for reference only.

It's blue! It's skinny! It's the Arduino Pro! SparkFun's minimal design approach to Arduino. This is a 5V Arduino running the 16MHz bootloader (select 'Arduino Duemilanove w/ 328' within the Arduino software). The power switch was moved to the side of the board (good idea Limor!) to allow control when a shield is attached.

Please note: The right-angle power switch is fragile. We're working on making the switch stronger. For now, please be gentle.

Arduino Pro 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 Duemilanove. It's a great board that will get you up and running quickly. The Arduino Pro series is meant for advanced users that understand the limitations of system voltage (5V), lack of connectors, and USB off board.

We wanted Arduino Pro to be low profile. The DC power jack footprint is available, but not populated. We recommend running the board with a LiPo battery for better portability. You will need to use a 5v step up or DC to DC converter to get 5V from a 3.7V LiPo battery, see the related items below.

We really wanted to minimize the cost of an Arduino. The Arduino Pro is like the Arduino Duemilanove (same pin out) but to keep the cost low, 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 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.

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  • ATmega328 running at 16MHz external resonator. Select 'Arduino Duemilanove w/ 328' to get the delay functions to work correctly.
  • USB connection off board
  • 5V regulator
  • Max 150mA output
  • Over current protected
  • Reverse polarity protected
  • DC input 5V up to 12V
  • Resettable fuse prevents damage to board in case of short
  • Power select switch acts as on/off switch
  • 2.1x2.05" (53.34x52.08mm)



Looking for answers to technical questions?

We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

  • Nimphious / about 11 years ago / 3

    Might be a good idea to update the desctiption of this to suggest the Uno instead of the old Duemilanove boards for beginners.

  • NeilHooey / about 12 years ago / 3

    When can we expect the release of the next revision that will have less delicate components (power switch), and possibly a way to connect an XBee module directly to the board?

  • Quazar / about 13 years ago / 3

    This looks like a great board, but I am unclear on the Vcc voltage. The description above is clearly for a 5V board, but the linked schematic is clearly marked up for a 3.3V board.
    I assume that the board is populated with a 5V regulator where the 3.3V regulator is present in the schematic, but it would be great to get that cleared up.
    I'm adding a couple of these to my wish-list for my next order...

  • omnivescence / about 13 years ago / 2

    So, could I program one of these with the Tx, Rx, and RST pins on my Duemilanove?

  • Adrian3 / about 13 years ago / 2

    also noticed you use TH connector for FTDI board, but in the schematic it's SMD.
    out of curiosity, what does the FIDUCIAL package's purpose, between TX and RX?

    • Kevin Vermeer / about 11 years ago / 1

      Not an SFE employee, and this is an old post, but I'll respond anyways, [strike]since I have time on my hands[/strike] [strike]since I'm a nice guy[/strike] since I'm procrastinating.
      A fiducial is a bare copper mark, with no silk or soldermask over it, to which other copper features can be referenced. They enable better alignment of silk, soldermask, and drilling layers after the copper has been placed during the PCB manufacturing process, but their main purpose is as a reference point when doing automated assembly ('pick and place').
      They have no electrical function; in fact, they're usually isolated from any signals.

  • Midknight5000 / about 10 years ago / 1

    You guys need to update the link in the arduino buying guide to go to the replacement.

  • This great board as with all other Arduno boards can be programed using Visual Studio. There is a free 100% Arduino compatible addin called Visual Micro. Arduino for Visual Studio

  • Member #122854 / about 11 years ago / 1

    I'm curious why the Wikipedia entry "List of Arduino compatibles" places this board in the "Superseded" category.

  • Dogcow / about 11 years ago * / 1

    I have browsed the earlier posts but couldn't see that this ambiguity in the description of the "green wire pin" has been mentioned :

    In the schematic the JP9 pinout reads thus: GND // GND // VCC // RX-I // TX-O // DTR

    While in the photos it is clearly: GND // GND // 3.3V // RX-I // TX-O // RTS

    Has there been a change sometime earlier or is the scematic simply wrong?

  • nmorisod / about 11 years ago / 1

    Hi, i've a question about the LDO regulator in this Arduino Pro. can you tell me which (part) regulator is used? because in the schematics it is not written. I need to know which one is used to check the spec of the part if it is suitable for my project.

    If i put 5V regulated in the external input(or RAW) will i get 5V at VCC? (after the regulator), i ask this because normaly LDO regulator have small dropout voltage but never saw a dropout voltage of 0.

    Thanks in advance.

    • MikeGrusin / about 11 years ago / 1

      It's a Micrel MIC5205. And you're correct, you need some headroom on your raw voltage to get regulated output. In your case, if you already have regulated 5V, you can feed that to the VCC pin which is downstream of the regulator.

  • Connie2 / about 11 years ago / 1

    Are the accessory kits for this still sold? I think there used to be a kit with headers/sockets, battery clip, and a plug that goes into the pro board. I am mainly in need of the plug with attached wires that go into the board. Is that still available on Sparkfun?

  • Member #239677 / about 11 years ago / 1

    hi, I have a USB to UART TTL Serial Converter, it has the following pins
    It uses a Sil labs chip
    would I be able to use this to pragram the board?

  • tonio4001 / about 11 years ago / 1

    Hello, I have a problem to uplaod a sketch into arduino pro.
    When soft is uplaod, green led is blinking. But at the end, arduino IDE say me :
    avrdude : stk500_getsync() : not in sync : rep=0x00
    avrdude : stk500_disable():protocol error, expect=0x14, reps = 0x51.
    Do you have an idea please ?
    best regards.

    • in the IDE, which arduino are you selecting? sounds like you have the wrong one selected.

      • tonio4001 / about 11 years ago / 1

        Hello, thanks.
        I choose : arduino pro or pro mini (5V,16MHz),w/ATMEGA 328.
        I think it's good no?

        • I've seen that error before. It either means you've selected the wrong board, your serial port isn't ready/working, or your board isn't ready.
          Try this:
          Are you using an FTDI Basic, or a cable? You might need to do a reset on the board to get code to upload if you aren't using the FTDI Basic. If you aren't using either, that might be your issue.
          Try another computer if possible, or another FTDI.
          If that doesn't work, contact

          • tonio4001 / about 11 years ago / 1

            Thank you very much. I chose a wrong Com port. i use FTDI 5V cable.
            best regards.

  • Microman / about 11 years ago * / 1

    Don't you guys mean UNO not Duemilanove fOr the first-time-user recommendation?

  • EvanT / about 11 years ago / 1

    I noticed in the pictures the serial headers are now through the hole. Is that new?

  • TECH GEEK / about 11 years ago / 1

    Why is there a buzzer in the schematic but not in the discription or pictures?

    • MikeGrusin / about 11 years ago / 1

      If you look at the Eagle files, you'll see that there's a location on the board to solder a buzzer if desired (it's not included). They're the two holes above and below the "Arduino Pro" text.

  • alphaman1101 / about 11 years ago / 1

    When are you guys supposed to be getting these back in stock? This board would do great for modding my motorcycle (GS500f). Im going to be replacing the stock gauges that are off quite a bit.. (indicates 110 mph, when truly im doing approximatively 85)

  • disabelle / about 11 years ago / 1

    im sorry im still new to this but the little section by the power switch is that a power connector i see like if i wanted to solder a battery pack to the board instead of using a lipo?

  • Pneumatic / about 11 years ago / 1

    I'm trying to get the board to output a 300 Baud serial signal, but I keep getting garbage. 1200->115200 all seem to work, so I suspect this is just a timing issue.
    Do you know if it's likely an issue with the board, or with the FTDI cable I'm using?

    • Chagrin / about 11 years ago / 1

      If you're using hardware serial the ATMega328 itself is probably at issue; it lacks enough register space to time the long delays needed for the low baud rates.

  • erebus / about 11 years ago / 1

    Well, I finally got around to using one of these tonight and I plugged it into an external 12V power supply. I must not understand what I am doing because I used the Vin and Gnd pins and when I turned on my power supply sparks and smoke exploded from what now looks like U2, R11, and maybe C19. It also burnt the connection on the bottom of the board that goes from Vin to C19. Unfortunately I unplugged wires from my power supply to the Pro before I looked to see if I had hooked them up backwards or had some wires crossed and or bridged. I don't see solder bridges or anything, and it still works fine when plugged into USB. Any ideas as to what I might have done to cause flames from the underworld to shoot forth and fry not only my retinas but components on the board as well??

    • / about 11 years ago / 1

      Was it an unregulated wall wort? A 12 volt unregulated will only output 12 volts at a specific theoretical load. In general this means it will output a voltage that is greater than but does not far exceed 12 volts. Under some circumstances it could even output double that amount. 12 volts is the maximum the board can handle, so even just 10% over could damage it. It would probably be better to use a 9 volt supply next time.
      On the other hand hooking it up backwards would do it as well. In general the safest option is to solder in a dc power jack and use a wall wart sold by spark fun. The li-po battery is also a good option, just make sure to get the 7 volt version.

      • erebus / about 11 years ago / 1

        It was actually an AC/DC power supply. I was running at 12V because I am powering other things that need 12 volts that are then controlled by the arduino. I have since decided it is a better idea to have my own voltage regulator in the mix before the raw in. I think it was probably hooked up backwards however. Wish I had not pulled all the wires off so fast. stupid magic smoke =(

  • aplejuce / about 11 years ago / 1

    My brain is not strong enough to comprehend... Does the battery connection pass through a boost controller to bring it to 5volts, or does it expect a 5 volt battery? Thanks in advance!

    • / about 11 years ago / 1

      it accepts a range of 5-12 volts, so anything less will most likely not work

  • Pneumatic / about 12 years ago / 1

    I'm having some problems with the 5V16Mhz model. The resettable fuse seems to be tripping at around 150-200ma.
    I'm using the Freetronics POE ethernet board fed with 12 V to try to power my project. The 12V from the board is fed back down the Vin pin. However, the 5V regulator seems to be cutting out regularly:
    When I measure the current draw at the Vin pin, it's only sinking ~210mA. I know the 328 can only source 140, but the fuse is supposed to handle 500mV, right?

    • Pneumatic / about 12 years ago / 1

      It turns out that the voltage regulator on the Arduino Pro board is really wimpy. I built my own 7805 based voltage regulator and it seems to be working fine now. At 150mA, it is unlikely to be able to power a standard Ethernet shield, since the WizNet 5100 chip is spec'ed to draw over that all by itself.

    • Pneumatic / about 12 years ago / 1

      Oops.. I meant 500mA, not 500mV.

  • GTMEstudent / about 12 years ago / 1

    I am seeking for enlightenment here.
    On the "Arduino Pro 328 - 5V/16MHz" board there is an oscillator. Although in the schematic the frequency of the oscillator is not specified but I am assuming it is 16MHz as the name of the board suggested.
    But the ATMega328 chip itself has an internal oscillator of 20MHz.
    My questions are:
    1. Why is the oscillator needed if the MCU has its own built in clock source?
    2. If two clock sources with different frequencies are present, how are the functions which involved timing coordinated? (ex. serial communication, pwm generation, some arduino built in functions like pulseIn(), delay() and so on)
    If someone can help me broaden my limited scope of knowledge I will greatly appreciate it.
    Thank you,

    • J.R. / about 11 years ago / 1

      The internal clock is not all that accurate, and can only go to 8 MHz (I believe). The ATMega 328 can run up to 20 MHz, but only with an external resonator of some kind. You select which resonator (internal or external) when first using the ATMega chip (SparkFun already does this for you)
      1. To be more accurate/ go faster.
      2. Only 1 source is used.

  • LoganWilliams / about 12 years ago / 1

    My Arduino Pro works fine when I first plug it in (using USB FTDI cable), and for a "little while" (~5 minutes) after. I can press the reset button, the green LED will flash, and I can upload from the Arduino software. However, it stops working shortly after that, and the green LED will no longer flash when I press the button, and I am unable to upload from the Arduino software. Disconnecting and reconnecting power does not help.
    However, if I disconnect power and leave the board for about an hour or so, the whole thing starts over again.
    Any ideas?

    • Not really, that behavior sounds pretty erratic. Contact tech support at

  • tomorrow_today / about 12 years ago / 1

    The Arduino Pro has considerable space on the pcb that can be used to upgrade its functionality without increasing the cost of the board. Although there are many similar things that can be done, I suggest using the empty space to put in the connector space for an Xbee socket and run a couple branches for the rx and tx. If, you're really feeling saucy you could even throw in holes and traces for jumpers or switches to change which digital pins the Xbee communicates on.

    • tomorrow_today / about 12 years ago / 1

      Oops, there are some resisters and diodes to add too, but I would definitely buy the board if I could plug in my Xbees directly instead of through a shield or explorer board.

      • Pearce / about 12 years ago / 1

        We'll take that into consideration for the next rev.

        • tomorrow_today / about 12 years ago / 1

          ...and this is why Sparkfun rocks. Thanks for your fast response.

  • Member #138680 / about 12 years ago / 1

    Just a check, the PWM output is 3,3V or 5V?

    • N8B / about 12 years ago / 1

      5V, all the I/Os operate at 5V.
      The ADC also shouldn't exceed 5V.

  • Allan2 / about 12 years ago / 1

    I don't understand why a crystal wasn't used. It can't be that much cheaper to use a resonator. And it's not like they're that tall either.

    • Mostly because I was going for cheap/small. It makes sense on the mini-pro but you're right, we could have used an xtal on this version.

  • ThiSel / about 12 years ago / 1

    I can program the board only once for each power up.
    After a sucessful program, the program runs. When I try to upload a new sketch, the upload fails; I assuming it's not resetting.
    If I power-cycle the unit (unplug the FTDI cable) and upload the sketch, then a new sketch can be programmed.

    • The FTDI cables does not do a reset. The FTDI basic breakout that we make does. I think that's probably the issue.

  • ZetaPhoenix / about 12 years ago / 1

    tetsujin: Clint-: can you use 3.3v on this board or does it only run on the full 5? if its only 5v why does it say 3.3 on the pic? I'm very new to this =)
    They used the same PCB design for both the 3.3V and 5V versions of this board, basically.
    It's important to note that both voltage pins on the shield connector (3.3V and 5V on a full-featured Arduino) are tied together on the Pro. On the 3.3V version they both output 3.3V, on the 5V version they both output 5V. In many cases this is probably fine, but you should be careful of it. If shield hardware connected to the 3.3V pin really can't operate at 5V, then you shouldn't connect it to this board.

    Adding a trace that can be cut (or a 3.3v regulator) to remove power to this pin should be added

    • That is a good idea. We will check into that. In the meantime, instead of cutting traces, you could just not connect that pin on the shield.
      But everyone should know, the 5V is 5V and the 3.3V is 3.3V. They do not do multiple voltages like the Arduino Main board.

  • tetsujin / about 12 years ago / 1

    Clint-: can you use 3.3v on this board or does it only run on the full 5? if its only 5v why does it say 3.3 on the pic? I'm very new to this =)
    They used the same PCB design for both the 3.3V and 5V versions of this board, basically.
    It's important to note that both voltage pins on the shield connector (3.3V and 5V on a full-featured Arduino) are tied together on the Pro. On the 3.3V version they both output 3.3V, on the 5V version they both output 5V. In many cases this is probably fine, but you should be careful of it. If shield hardware connected to the 3.3V pin really can't operate at 5V, then you shouldn't connect it to this board.

  • Why not connect the ACD6 and ADC7 pins? I understand space is a premium on the pro mini board, but why leave them off here? I'm going to try soldering on my own.

    • salsa / about 12 years ago / 1

      Yeah, plated through-holes for an extra 2-pin header would be a great addition for the next version! Might need to move the ATmega and a few other components towards the digital pin side to free the space near those pins. Also, since through-holes are free (right?!) how about adding SPI and I2C headers?

  • zachtos / about 12 years ago / 1

    I've used around 20 of these boards to build my IRcombat laser tag game (infared guns, smart flags and frag grenades). Works great. I wish I ordered all of them as the pro version instead of the full USB ported version. Smaller and cheaper. I already wish they sold a version with more RAM and more Flash memory. I have this thing maxed out. (and yes, I know about the mega version, and that's too bulky physically)

  • jkozniewski / about 12 years ago / 1

    Is it possible to make this (5v) model to work with
    one of yours LiPo batteries ? All of them are nominal 3.7v but in description above you're stating that "We recommend running the board with a LiPo battery for better portability."
    Thanks for any advice :) !

    • salsa / about 12 years ago / 1

      Ditto- how does this run off a LiPo pack?
      Looking at the EAGLE files, it's unclear what U2 is. It's clear it's a regulator, but is it stepping up 3.7V form a LiPo to 5V, or is it a placeholder for a 5V regulator in the case of this board, or a 3.3V regulator for the 3.3V board? What is U2?

  • Cool board, however the surface mounted components are very fragile. The first day the switch broke off, although it was simple to re-solder that. Just tonight the serial headers broke off, and I'm at a loss. They can not be soldered back, so I suppose I've got to wire up an entirely new serial port in order to program it again.
    Stick with the pro mini if you can. I had to use this simply because I needed the AREF port which was omitted on the mini.
    On a side note: this 5V board boots and programs fine with the 3.3V FTDI/USB connector.

  • Aerodyno / about 12 years ago / 1

    What is the acceptable operating temperature for this board? Important to know, as I think a few of my boards have failed.

    • promethean / about 12 years ago / 1

      The max temperature rating for the ATmega328 is 85' celcius. Beyond this you risk chip failure or premature data loss. The 85' should be taken as an absolute max though, since some discrete components, even if they don't fail, will have temperature coefficients that describe potentially significant changes in behavior as low as the 45'-65' range. For this reason, for any highly calibrated or sensitive project, you will want to research the specific temperature ratings and coefficients of the components you are using.
      Now, all of that said, for troubleshooting purposes you may want to provide some details on your project and how you lost your boards, since these are designed for the momentary heat of a soldering iron, and operating temperatures in excess of ~60' would be difficult to achieve with the arduino board alone and correct voltage.

  • dosuserx2 / about 12 years ago / 1

    will this charge a LiPo if connected to a USB card or do i need an additional LiPo recharger?

    • Pneumatic / about 12 years ago / 1

      It won't charge the LiPo, or any other sort of battery you connect. That would have to be build separately, (and be very careful if trying to build your own LiPo charger, getting it wrong leads to explosions and fires.)

  • Clint- / about 12 years ago / 1

    can you use 3.3v on this board or does it only run on the full 5? if its only 5v why does it say 3.3 on the pic? I'm very new to this =)

  • eddiem / about 13 years ago / 1

    I have a bunch of these. About three weeks ago I tried to reprogram the flash on one of them.
    Unlike the 168 version I could not manage to read the flash. Perhaps the security bit was set?
    I presumed it was my old kanda software was to blame. It doesn't know about 328s but usually I can find a similar part and get the kanda programmer to work.
    So I ended up with around 6 different software packages including AVRdude. AVRdude was the only one with a 328 device listed but it didn't work with my kanda programmer or the SF parallel programmer.
    So I bought a USB pocket programmer. This had issues too but ultimately I got it to run.
    It would go through the program cycle but not verify.
    Reading back the flash showed it was partly programmed but on average ever second page was blank (ff).
    I went back to the kanda and found exactly the same thing. I tried extending the programming time but nothing helped.
    Continued in part2.

    • eddiem / about 13 years ago / 1

      In the end I grabbed a new pro-328, added ISP pins and tried it on the kanda.
      This one programmed and verified first time and my program ran.
      So it seems the orginal 328 is somehow faulty. I'm pretty sure the orginal bootloader was working so they obviously managed to programme it in the factory but they possibly didn't use ISP.

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