Uno Plus+

An Arduino UNO Compatible Board with isolated Glowing headers and some Extras

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If its not broken don't fix it, just add some more features.

The Uno Plus+ is An Arduino Uno Compatible Board with a twist. All the components are on the bottom giving ample space to clearly label all the pins and even label the second and third function.

The Goal of the Uno Plus+ it to take the Arduino Uno, and make it even easier to use. An by adding isolated LED indicators on the IO Pins Debugging and Teaching can be even easier for teachers and student in the STEM Field. With the addition of a Stemma/Quiic connector and an integrated addressable LED can speed the process of developing your next Project.

An as always this project is completely open source and all design files will be updated to the most current revision below. You can build your own Arduino comparable Uno+ and flash the Firmware with the instructions below.

With Glowing Headers

Without Glowing Headers
Analog Pins  (A0 - A5)
Digital Pins  (D0 - D13)
All Analog Pins Use a Op-amp to
 "MAP" the 0-5V Voltage to a relitive intensity
of the LED
All Digital IO Pins use a comparator with a
Schmitt Trigger that will trigger similarly to the Schmitt trigger built into the Atmega 328.

Pin A5 is being tested with a voltage sweep 0-5V
Pin D7 is being tested with a voltage sweep 0-5V

                         Bill of Material

                           Gerber Files



Glowing Header - Rev

x-zip-compressed - 5.98 MB - 05/14/2023 at 01:18


Bottom - Layout.JPG

JPEG Image - 541.06 kB - 04/25/2023 at 04:35


TOP - Layout.JPG

JPEG Image - 455.97 kB - 04/25/2023 at 04:35


Arduino Uno Plus - Rev1 - Sch.pdf


Adobe Portable Document Format - 859.30 kB - 04/08/2023 at 04:32


Arduino Uno Plus - Rev1 -

Gerber Files

Zip Archive - 950.45 kB - 04/08/2023 at 04:26


View all 6 files

  • 1 × ATmega328P-MU Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × ATmega16U2-MU Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 3 × LM339DR Amplifier and Linear ICs / Comparator ICs
  • 2 × LM393DR2G Amplifier and Linear ICs / Comparator ICs
  • 1 × LM358DRG Amplifier and Linear ICs / Operational Amplifiers

View all 50 components

  • Fiber optic Test​

    John Loeffler08/18/2023 at 22:46 0 comments

    Fiber optic Test

    Thank you  James Newton   For the Suggestion.   Adding a fiber optic cable just might work.    I used a PMMA Side emission cable an the results seem promising

  • Glowing Headers

    John Loeffler04/27/2023 at 20:03 0 comments

    LED indicators are one thing But if we make the whole header glow the ease of identifying the right pin becomes greater for entry level users

  • Analog input LED

    John Loeffler04/25/2023 at 02:57 0 comments

    Unlike the Digital IO pins the analog pins have an led driven by an Opamp and Summation circuit that will map the LED to the Voltage.  So the LED will glow with the intensity proportional to the Voltage 0-5V

    The Analog LED Circuit is as Follows

    The Opamp Acts as a high impotence buffer So it does not influence any analog input to the pin.  A Summation  Network is crated to lower the voltage before it gets fed through a 66k Resistor then into a NPN Transistor to drive the Current to the LED


    The Real World Test of this circuit show that the current configuration does a decent job of making the pins Voltage to the Intensity of the LED.

  • Schmitt Trigger

    John Loeffler04/01/2023 at 03:54 0 comments

    The Atmega328P Has an internal schmitt trigger on all Digital IO Pins.   The Schmitt trigger is a great way to reject the Noise of a Digital Pin Especially one that is Left Floating.  In addition adding a Comparator to the LED Circuit isolates the pin due to the high input impedance of the Comparator.

       However the ATmega 328P does not Express the hysteresis of the Low and High Logic Level.  

      So the People over at RadishLogic Ran the 328P Pins.

    Radishlogic - Schmitt Trigger Test

     RadishLogic Found that when using USB Buss as the Power the Low High Logic Levels were

    Logic Levels

    Using 33k, 36k, and 150k a comparable Schmitt Trigger can Be Created

    Further Testing on PCB Should be conducted to alpine the Schmitt Trigger of Atmega328 to the LED Comparator 

    Implementing into the Arduino Plus+ Pin seven is set to digital IO and  a modified Button Sketch is used. 

    So the real world test of the Schmitt trigger show that

    1) The LED Low input State Triggers at 2.29V      ------   At Atmega Triggers at  2.44V  --- 2.23% error

    2) The LED High Input State triggers as  2.52V   ------   At Atmega Triggers at  2.52V --- 0% error

  • Goals

    John Loeffler04/01/2023 at 03:45 0 comments

    The Goal of this Project is to Crate a STEM Oriented Using the Microcontroller that started It all.


    1)The Core of this Will Be an Arduino Uno with the 16U2 USB Uart.

    2) Every Pin will have a LED Attached to it to show the Status.

    3) ALL LEDs will be isolated using A Follower Op-amp and Comparitor circuit.

    4) Digital IO Pin LEDs will be Equipped with a Schmitt Trigger that is close to the internal Schmiit Trigger in the Atmega328P

    5) Analog Pin LEDs Will illuminate proportionate to the Voltage of the Pin (0V=off,  2V=2mV, 5V=5mV)

    6) A Toggle Switch to turn all LEDs Off

    7) The LEDs will Be Reverse Mount and Diffused with Epoxy

    8) Placing All components on Bottom allows For ample Space to Label all Pins with all Functions.

    9) Electronics will be coated in Epoxy to be more STEM Friendly ( Drops, Spills...)

    10) Design for Manufacture


    1) STEMMA/QWIIC Connector

    2) Neopixel on Pin 6

    3) RTC

    4) SD Card

    5) Speaker

    6) Full Color Silkscreen for ease of pin identification

View all 5 project logs

  • 1
    Soldering Top SMD Components and LEDs

    Bottom Solder Layout

    Solder all Bottom Bottom Components First

    Solder LED Components

    - LEDs Are designed to be mounted in reverse. Some LEDs require a little force to fit in the hole in reverse.

  • 2
    Solder Top Components and LED's

    Top Solder Layout

  • 3
    Flashing Uno/Genuino Firmware

    Download the Following 2 Hex Files




    Atmega 16u2 Fuses

    LFuse = 0xFF

    HFuse = 0xD9

    EFuse = 0xF4


    Atmega 328P Fuses

    LFuse = 0xFF

    HFuse = 0xDE

    EFuse = 0x05

View all 3 instructions

Enjoy this project?



Aben wrote 02/20/2024 at 13:29 point

Thank you for your sharing. I tried to do it myself. I encountered a problem when burning ATmega16u2. Can you share how to burn Arduino Uno firmware?

  Are you sure? yes | no

John Loeffler wrote 02/21/2024 at 14:31 point

I use Microchip Studio (

Also there is a way to add the 16u2 as a board in the Arduino IDE and lets you Burn the Bootloader.  I can't find that tutorial at the moment

  Are you sure? yes | no

Aben wrote 02/22/2024 at 00:40 point


I encountered a problem. USB can recognize the model of atmega16u2. Every time using dfu-programmer enters dfu mode, "read" will report an error. After erasing and re-flash the firmware, it will be ok. Once restarted, the error will continue. Since I don't have any magnetic beads, I temporarily soldered a resistor instead.

The reason may be that there are no magnetic beads or that some pins are not soldered firmly?

  Are you sure? yes | no

John Loeffler wrote 02/22/2024 at 13:33 point

I NEVER did it thru DFU mode,

Use this tutorial and create a custom 16u2 board

  Are you sure? yes | no

Aben wrote 02/22/2024 at 15:47 point

thanks for your help

I followed step by step and successfully burned the 328p and 16u2 firmware.

It works!

  Are you sure? yes | no

Aben wrote 01/13/2024 at 17:42 point

Thank you very much, it's a great project. Could you design a version that uses CH340G instead of ATmega16U2?

  Are you sure? yes | no

James Newton wrote 06/21/2023 at 19:20 point

I like this. Consider using bits of thick fishing line to /optically/ connect devices via phototransistors so you can actually "see" the signal go down the "wire". You could even make small logic gates which sense and produce light to teach digital logic. All logic can be done with NAND gates:
It's also possible to do some limited analog computing or use PWM to simulate analog in a way that humans can "see" but with greater precision in the transmitted signal (less affected by ambient light).

  Are you sure? yes | no

John Loeffler wrote 07/18/2023 at 15:37 point

good idea.  Might have to try that 

  Are you sure? yes | no

Nicolas Tremblay wrote 05/26/2023 at 14:22 point

I hope this goes to a Kickstarter, CrowdSupply, Tindie or other. It's a really great idea. I'll take 3.

  Are you sure? yes | no

gedm-dev wrote 05/14/2023 at 04:35 point

Very nice and super stylish.

  Are you sure? yes | no

Martin Zimmerman wrote 05/11/2023 at 18:55 point

Where did you source the glowing headers?  Can you share port numbers and suppliers for them?

  Are you sure? yes | no

John Loeffler wrote 05/11/2023 at 19:53 point

I made them

  Are you sure? yes | no

Dan Kisling wrote 05/12/2023 at 15:04 point

Did you 3D print them? Can you share the files?

  Are you sure? yes | no

John Loeffler wrote 05/14/2023 at 01:46 point

Sure,  I added it

  Are you sure? yes | no

Dan Kisling wrote 05/16/2023 at 18:39 point

Thanks for uploading! I tried printing them myself on a resin printer. Worked pretty well. Headers are functional - but a little more annoying to use than regular headers due to added friction (and assembly time). Very cool concept! 

  Are you sure? yes | no

ChengDanguo wrote 04/20/2023 at 09:28 point

A very cooooooooool ATmega,that is really helpful,i think.

  Are you sure? yes | no

Dylan Brophy wrote 04/10/2023 at 19:17 point

That is a *really* pretty board.

  Are you sure? yes | no

Ken Yap wrote 04/02/2023 at 04:07 point

That's cool and very useful. I've lost track of the number of times I've counted pin socket positions to insert leads. I wish they had been built your way from the beginning. I'm waiting for the R4 though. But there's still a lot of life in the R3.

  Are you sure? yes | no

Brett Smith wrote 03/31/2023 at 20:34 point

Beautiful! Well done!

  Are you sure? yes | no

LicinioFortunato wrote 03/23/2023 at 20:29 point

can you pass the schematic and all tms?

  Are you sure? yes | no

Peabody1929 wrote 03/09/2023 at 17:58 point

Where's the beef?

  Are you sure? yes | no

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