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Yet another 3.3Vizing an Arduino

In this post we present some suggestion, “overclocking” on 3.3V and 16MHz Arduinos.

Processors from Atmel are usable on both 5V and 3.3V logics. For example, ATmega328P on Arduino Pro Mini or ATmega32U4 on Arduino Leonardo (Arduino Pro Micro) can work on both voltages without problems. But only one consideration is remained: 16MHz clock is not OFFICIALLY supported by Atmel if the processor is on 3.3V. So if you use these processors at 3.3V AND 16MHz you must understand/agree you are in danger(!) of overclocked them. (However, in many cases it should be safe and no problem.)

In this post we’ll do two overclocking experiments:

  1. Arduino Pro Mini 328 5V 16MHz → 3.3V 16MHz
  2. Arduino Leonardo (5V 16MHz) → (3.3V 16MHz)

1. Making Arduino Pro Mini 328 3.3V 16MHz
If you want Arduino Pro Mini 328 3.3V “16MHz” then there might be another way: Buy a genuine Arduino Pro Mini 328 3.3V “8MHz” and change the crystal (CERALOC® = ceramic resonator) on it. The problem is NO COMPATIBLE CERALOC® exists for the original one (original part no. is Murata CSTCE8M00G55A-R0). To be more precise, Murata makes a similar CERALOC® of 16MHz (part no. Murata CSTCE16M0V53-R0) but their footprints differ and 16MHz version can’t fit to the 8MHz place. So this method to change the crystal is not so easy to go through.

Thus we try the other way: Buy a genuine Arduino Pro Mini 328 “5V” 16MHz and change the voltage regulator on it. Photo: The location of regulator is marked red. The original voltage regulator is Micrel MIC5205-3.3YM5. It is the LoHS version of Micrel MIC5205-3.3BM5 and the footprint is SOT-23-5.

(Sorry. I forgot to take a picture of original Arduino Pro Mini 328 5V 16MHz. The voltage regulator in this photo has already replaced by a 3.3V regulator.)

I used some low temperature solder (Removal Alloy by CHIPQUIK®) and two soldering irons to remove the SMD regulator. Detailed instruction of removing SMD parts is there in CHIPQUIK® site.

The replacement part should be any 3.3V voltage regulator that holds certain conditions. If you happen to get a Micrel MIC5205-3.3YM5 (LoHS) or Micrel MIC5205-3.3BM5 (non-LoHS) then you are very lucky to use the best one. However, the required conditions are, I think, only “3.3V fixed voltage”, “low dropout”, “150mA”, and “SOT-23-5” so there are many choices in buying a compatible regulator.

I used a Toshiba TAR5SB33 for the replace, because it is already there just in my parts-box. Soldering a SOT-23-5 part is not so difficult and is fun!

After soldering, connect the Arduino to your PC and check how it works (Don’t forget to use 3.3V version of FTDI board!!). In Arduino IDE, [Tools]→[Board] should be “Arduino Pro or Pro Mini” and [Tools]→[Processor] should be “ATmega328 (5V, 16MHz)” (Note: Arduino IDE doesn’t care about the voltage).

2. Making Arduino Leonardo (3.3V 16MHz)
There is a great article by Tyler Cooper on replacing Arduino Uno’s regulator to a 3.3V version. Arduino Uno and Leonardo are nearly identical around the power circuit (you can compare their schematics: Uno, Leonardo) so we could do the same on Leonardo, too.

However, the method Cooper used for Uno is not good for Leonardo who can speak some of USB protocols. Because after his surgery of removing the fuse XUSB signal doesn’t reach Uno’s (or Leonardo’s) processor pin but nowhere. USB 2.0 protocol requires XUSB (= VUSB) line to be alive (for checking impedances to D+/D-) at least speed negotiation phase thus the line shouldn’t be remained at infinite impedance or open after the surgery.

So I didn’t remove the fuse but did remove the MOSFET (T1 FDN340P in the schematic) marked red in the following photo.

(Sorry, again. I also forgot to take a photo before removing/replacing something. In this photo the MOSFET has already removed, the voltage regulator replaced, and the additional diode attached.)

The rest of the surgery is the same as Cooper’s method: Replace the voltage regulator to a 3.3V version and connect VUSB to voltage regulator’s input pin through a diode. I used Advanced Analog Circuits AZ1086H-3.3 (SOT-223 package) for voltage regulator and 1N4007 for diode, however, any similar ones will do.

After removal and soldering things, connect the Arduino to your PC and check how it works. In Arduino IDE, no changes in settings are required (i.e., [Board] is also “Arduino Leonardo” and that’s all).


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GoPro from CANON Timer Remote Controller

Canon TC-80N3 is an advanced cable remote controller for EOS cameras. This post is to connect TC-80N3 and GoPro.


  • GoPro Hero 3+ Black
  • MewPro + Arduino Pro Mini 3.3V (Teensy 3.x or GR-KURUMI are also usable but we’re not going to show how-to in this post)
  • Canon Timer Remote Controller TC-80N3
  • some wires and solder

Basically TC-80N3 consists of two independent switches for shutter and focus. It remotely make corresponding circuits inside your camera CLOSE or OPEN. The difference between a mechanical switch and TC-80N3 is it bounces or not. To learn about contact bounce (aka “chatter”) see, for example, Wikipedia. Because TC-80N3 is specially crafted for shutter so that doesn’t bounce we can directly connect it to one of interrupt pins (INT0 or INT1) of Arduino Pro Mini without any additional circuits or software debounce routines.

Proprietary Connector
In order to connect TC-80N3 to Arduino its proprietary connector (N3-plug) may be an obstacle. If you don’t mind cutting your TC-80N3 cable then go to the next section “Connection”.

There are some places where N3-plug converters are purchasable:

These cables convert N3-plug to 2.5mm stereo phone plug (male connector), then you can easily find a receptacle that can mates with it.

The signals inside both TC-80N3 and its conversion cable are clearly explained in this article.

Then we solder the shutter signal to INT0 and the ground to GND as follows:
(The focus signal can be remained open.)

Software Mods
Open MewPro sketch in your Arduino IDE. Find the following lines in MewPro.ino file:

// e_Shutters: One or two remote shutters without contact bounce or chatter

And change the lines like this:

// e_Shutters: One or two remote shutters without contact bounce or chatter

This enables to compile two routines in e_Shutter.ino (one is the interrupt handler and the other is the initializer attaching the handler to the actual signal pin (INT0)).

Then connect FTDI temporary header and USB cable to your PC, and install the software to Arduino Pro Mini.
That’s all. Enjoy!

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How To Use MewPro and Its Application

We will show you how to use a first time MewPro. Basics to control GoPro camera will be explained. No external sensors involved (Maybe in following posts, we can show you some examples of sensor usages).


In order to use MewPro as a GoPro controller you need the following hardwares:

GoPro Hero 3+ Black
Neither previous editions nor Hero 3+ Silver work with MewPro. Hero 4 Black will be expectedly supported but we don’t promise this. (Update: Hero 4 Black/Silver are supported by MewPro 2/Cable. Please refer recent posts for them.)
SMD parts, Herobus connector and Arduino Pro Mini 3.3V 8MHz are soldered. If you want to use a higher performance microcontroller then Teensy 3.1 and GR-KURUMI are supported by the MewPro application.
Arduino Pro Mini Temporary FTDI Header
If you buy a MewPro from our shop the header is included in the package.
Sparkfun FTDI Basic Breakout – 3.3V and USB cable
Use 3.3V version of the breakout board. Any compatible board should work.

Remark: If you use Teensy 3.1 in the place of Arduino Pro Mini then you don’t need Temporary FTDI Header and/or Sparkfun FTDI board; and please consider to buy our Arduino Pro Mini / Teensy 3.1 Conversion Board.

Teensy Warning: If you use Teensy 3.1 with MewPro, please cut the PCB pattern between VUSB and VIN (On the a-lot-of-pad-side of Teensy board there is the special slit between pads to do so). Because MewPro uses RAW input from GoPro battery (about 3.8V). So if you connect VUSB (5V) to MewPro’s RAW then GoPro’s battery pin will become 5V. This will destroy your GoPro.


Arduino IDE 1.5.7 beta or newer
Older versions of Arduino IDE have bugs in Wire library that cause MewPro unusable.
MewPro Application
This is an open source software (MIT license). You can modify and distribute it as you like.

Remark: If you use Teensy 3.1 or GR-KURUMI, you must be a wizard or witch so maybe you know what is required a kind of softwares instead of above mentioned Arduino IDE.


Install Arduino IDE on your PC and launch it. In Arduino IDE [File]→[Open...]→ then open MewPro.ino.

Remark: MewPro.ino contains the following files as tabs; a_Queue.ino, b_TimeAlarms.ino, c_I2C.ino, d_BacpacCommands.ino, e_Shutter.ino, f_Switch.ino,g_IRremote.ino, h_LightSensor.ino, i_PIRsensor.ino, and j_VideoMotionDetect.ino. If you like to see what will be happen inside of your Arduino Pro Mini you could read any of them.

Connect MewPro to your PC w/ FTDI board and the temporary header.
Then connect them to GoPro Hero 3+ Black.

In Arduino IDE application, select [Tools]→[Board]→[Arduino Pro or Pro Mini], [Tools]→[Processor]→[ATmega328 (3.3V, 8MHz)], and [Tools]→[Port]→[(the port where you connected the FTDI cable)]. Then “Verify” the MewPro sketch and “Upload” it to Arduino Pro Mini board.

Remark: If you are using Teensy 3.1 c_I2C.ino will fail to compile. Just change the first four lines to
#if defined(__MK20DX256__) // Teensy 3.1
#include <i2c_t3.h> // *** please comment out this line if __MK20DX256__ is not defined ***
#else // Arduino Pro Mini
//#include <Wire.h> // *** please comment out this line if __MK20DX256__ is defined ***

Control GoPro

Open “Serial Monitor” in Arduino IDE window (click the the top right “magnifier” icon). Set [57600 baud] using the bottom right pulldown, [Newline] the middle pulldown, [Autoscroll] the left box checked.

Type ‘@‘ (one letter representing at sign) in the input area of Serial Monitor, and hit return key.

The message “camera power on” is shown and your GoPro Hero 3+ Black turned its power on.

The messages on “Serial Monitor” shows communication details between Arduino and GoPro. If this is the first time to connect your MewPro to GoPro then repeated erroneous “>01 08” is shown again and again. This is because the I²C EEPROM on the MewPro board is not properly initialized yet. So let’s type another one letter command ‘!’ (exclamation mark) in the input area of Serial Monitor, and hit return key.


Then other messages come from GoPro.
“role change” means that the role as a BacPac™ has been changed. This time the role is “master” (to understand the roles and modes of Dual Hero BacPac™ please refer our previous post).

In “master” role, we can’t push the shutter botton. But we can get composite video signal out of Herobus connector by using “VO1” command, which “master” MewPro automatically send to GoPro as shown in messages of above screenshot.

Next change the role to “slave”. To do this, type the one letter command ‘!’ again. The command ‘!’ toggles the role between “master” and “slave”.

You can see in the above screenshot various information is obtained from GoPro camera.

Now I²C EEPROM on your MewPro board is properly set to “slave” role. In the role we can push the shutter button of GoPro as usual. So we recommend using MewPro in this role.

Now we almost do every thing on GoPro from Arduino. Details of I²C commands are listed in our earlier post.

Try typing “SY1”. Then “SY0”. (Start recording! Stop recording!!)

If you finished type “PW0”. (This should power off your GoPro.)


Final Note: “SY1” command fails if the mode is different to the mode when GoPro is power on. That is if you change camera’s mode manually by using mode/power button of the camera body or “CM” (SET_CAMERA_MODE) command, then “SY” command will fail. This is due to GoPro firmware so please don’t blame MewPro. In order to workaround this restriction, use “DM” (SET_CAMERA_DEFAULT_MODE) command and set your camera to desired mode and “PW0” (power off). After this, try ‘@‘ (power on) and “SY1“.

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GoPro Hero 3+ Black slave mode

GoPro Hero 3+ Black can be controlled by Dual Hero BacPac™. In this post the protocol among two Blacks and the BacPac™, which is called “Smarty”, is roughly explained.

There are three devices involved:

  1. Master Camera
  2. Slave Camera
  3. Smarty

Role of a camera, Master or Slave is determined by the camera reading the first byte of I²C EEPROM located inside of Dual Hero BacPac™ connected; if the content of address 0 is 4 or 5 then the camera will play Master or Slave respectively.

After a camera knew its future role, it sends “vs” (GET_BACPAC_PROTOCOL_VERSION) command to Smarty (Please refer the other post about the detail of I²C commands).

Then Smarty respond to both “vs”s as OKs then each camera enters to each role; Master send the configuration of the camera (mode, pixels, upside-down and so on) to Smarty; and Smarty send the heard info to Slave; …

It is not so obvious that Master or Slave has two modes:

  1. 3d_SYNC_MASTER: Route DSP sync signals to CCD sensor
  2. 3d_SYNC_SLAVE: Route Dual Hero BacPac™ generated sync signals to CCD sensor

Just after a Dual Hero BacPac™ has been connected, both Master and Slave camera are in the 3d_SYNC_MASTER mode. But after the negotiation of camera configuration etc. is finished, they both go into the 3d_SYNC_SLAVE mode. This way 3d video is “genlocked” by Smarty (NOT by Master).

You are now understand the basics. Then what we can do? Maybe almost all of us don’t need “genlock”. Because many of us have only ONE GoPro Hero 3+ Black, don’t we?

MewPro don’t choose the way of generating a “genlock” signal. Instead MewPro interfere the negotiation of two cameras and leave both of them in the 3d_SYNC_MASTER state. So we don’t worry about the precision of a “genlock” signal but we can easily control all of the functionalities of GoPro Hero 3+ Black as if MewPro were a Smarty.

Tomorrow I’ll post some demonstrations or screenshots using MewPro and Arduino Pro Mini.