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Topic: Oak Micros om328p Arduino Compatible (Read 7587 times) previous topic - next topic


The Oak Micros om328p with Arduino bootloader is a full-featured Arduino compatible with USB in a 28-pin 600mil format; that is twice the width of a mega328p PDIP chip but containing all of the circuitry required for full Arduino compatibility. There are even 2 extra LEDs for monitoring port I/O.

The om328p has a complete User Guide and Reference with details on how to setup and use the device. It has 22 I/O pins which includes the standard 14 digitial I/O pins and a full complement of 8 analog pins.

The om328p has similar function to the Arduino Nano but is smaller and simpler. This Youtube video of 16 om328p devices illustrates its small size compared to the Nano which can only fit 12 on a breadboard. The om328p has all of its components on a single side of a 2-sided PCB measuring 1.4" by 0.7" (36mm x 18mm). Think of it as an "Arduino Pico".

The om328p sells at an introductory price of $29.95 (same as the Arduino Duemilanove). Visit the Oak Micros shop to purchase the om328p or any of our other 9 microcontroller devices.

Mike Perks


This looks very promising.  I'm looking for a board that can fit into a computer mouse-sized enclosure for a project.  I'll review the documentation.

Coding Badly


The top of the board is very tightly packed as you can see so there wasn't quite room for any notation. Below is a picture of the underneath that does show the pin numbering. Pin 1 is near the USB socket and it is just a matter of counting around. The photograph also shows the (18 mil) round pins that I am using that will fit into a standard 28-pin IC socket or female SIP headers.

Here are a couple of pictures from the User Guide and Reference that show overlays of AVR and Arduino digital/analog I/O pins. The "top" 8 pins (1-4, 25-28) follow the usual "Stamp" format. I think you will find the documentation quite extensive in terms of covering configuration, setup, and use of the device.



Is that board only two layers?  That's pretty impressive!


Thank you westfw.

Indeed the board is only 2 layers, minimum drill size is 20mil and minimum track/spacing is 8 mil. Most power tracks are 12 mil and signal tracks are 8 mil.

I thought the FTDI QFN32 chip (FT232RQ) was going to be problematic but actually it worked out very well. As you can see from my website, this board is simply a natural continuation of previous work. I have a 40-pin USB board using a mega644p in testing which uses 15mil holes and some 7mil tracks.

Mike Perks


Very, very nice job, Mike!

I ordered one of these last Thursday, and it arrived today, Saturday. It was shipped via Priority Mail (USA) which was the least expensive option at $4.95.

I ordered the om328p with the Arduino bootloader. It booted up when I connected the USB cable to it, and the FTDI drivers (Win/XP, 32 bit) that had been previously installed for my Arduino Duemilanove/328 connected with the FT232R USB chip with no adjustments. Windows did not need to go through the "Found new hardware" dialogs. The om328p began to run its pre-installed sketch. Sweet.

All I did next was configure the serial port to 115200 baud and changed the latency timer to 2 msec as per section 2.4 of the User Guide, in preparation for uploading some of my existing Arduino sketches.

The Arduino IDE was already configured for my Arduino Duemilanove w/ATmega 328, so I selected the om328p's COM port and clicked the "Upload to I/O Board" button on a sketch I have in my sketchbook. It ran with no adjustments. Sweetness again!

I have uploaded and run a couple of other sketches with no changes. All are operating as expected.

This is one nice implementation. You can fit about six of these in the footprint of one Duemilanove. Hats off to Oak Micros for this board.


Jul 05, 2009, 06:19 am Last Edit: Jul 05, 2009, 06:21 am by mikeperks Reason: 1
Thank you for the compliments. A lot of people have expressed interest in this Arduino compatible device.

Although the om328p already has complete PDF documentation I thought it would be useful to have a complete device description on the Arduino wiki (just like Arduino boards).


This doesn't have 3V right?

I think more and more devices are working on 3/3.3V, this might be a missed chance? Maybe this is an idea for the future?

Anyway, great product!


Re 3/3.3V support:

There are some factors involved in running any Arduino at less than 4V.
  • The AVRs are only rated down to 3.6V with a 16 MHz crystal. You would need to use a 8 MHz crystal to achieve a voltage such as 2.7V or 3.3V.
  • The FTDI USB USART chip requires a minimum of 4V. That means any Arduino with builtin USB support needs at least 4V. That is why you will find that the Duemilanove, Diecimila, Nano and other boards all list 5V as the operating voltage.
The  specialist boards like the "Pro" and "Pro Mini" can use 3.3V but note they do not have a FTDI chip and use a 8MHz crystal.

You can use the Oak Micros om328p down to 3.6V providing that you do not want to use the USB port. As described in the User's Guide and Reference, it even possible to hook up a serial converter so that you can use serial communications at 3.6V. If you use less than 5V, then the User Guide and Reference recommends removing the om328p from the circuit before downloading a new sketch using the USB port. This avoids the 5V from the USB port "killing" any support circuitry connected to the mega328.

It would be definitely possible to produce a version of the om328p with a 8MHz crystal that supports voltages down to 2.7V but that all depends on the success of the om328p.


No, he's asking why the board doesn't have a 3.3V supply pin (coming from the FT232 or an external reg).


The om328p does not have a 3.3V supply pin from the FTDI chip simply because there is not enough available pins in a 28-pin package. That is also why AREF is tied to Vcc. The internal voltage reference is still available of course. It is simply a matter of compromise to fit everything into a standard 28-pin 600 mil socket.

I would also argue that the 50mA limit from the FTDI chip 3.3V output is somewhat limiting.

It is definitely possible to provide a version of the om328p with a 3.3V regulator and 8 MHz crystal. It would take a little PCB work to change the power routing for the FTDI chip. As I mentioned before this is not a showstopper and would simply a matter of reaching sufficient sales to justify the cost.


Hmm, I was not asking for just a 3.3V supply pin. I was more looking into something that Seeedstudio did with their Seeeduino.

It has a switch which can be set to either 5V or 3V. When switch is set to 3V, everything will work on 3V. Not just a supply pin, also the other pins.


Jul 07, 2009, 08:27 am Last Edit: Jul 07, 2009, 08:28 am by mikeperks Reason: 1
Thank you for the clarification CrashingDutchman and your continued interest in the Oak Micros om328p Arduino compatible.

The Seeduino has much more space on its PCB and can offer such an option. The om328p is designed to be very compact but yet socketable and breadboardable. It is also priced very competitively with other Arduino platforms. As in any design, some compromises were made and there is very little space to offer a 3V/5V switch or solder jumper.

One great thing about the Arduino platform is the wide range of devices and boards that use the same software tools, platform and design - you can pretty choose the features that match your application. The om328p sister product (ZX-328nu) and the ZBasic platform is another example of this idea.


My initial post that said "missed chance" maybe was a little harsh. Be assured that this wasn't my intention.

I understand completely about the size and that you are limited in adding components. I don't want to push you into a direction but, I think there is a market for a similar product as yours, but running at around 3V.

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