Configuration of RN52 through Simblee (RFD77101)

Simblee (RFD77101) is one of the best BLE (Bluetooth Low Energy) chip that turns your project into the IoT. Since I have learned how to use the Simblee, I have come up with the idea that I connect Simblee into RN52 (Audio Bluetooth) to make my project more fun. The first step that I needed to do was whether I could do the configuration of RN52 through a Simblee chip, so I will introduce how to configure it by using UART and display the configuration on the Simblee App based on the commands you input.

Normal Configuration

In order to do the normal configuration that you can find in Sparkfun tutorial of RN52, you need to use a FTDI chip with USB to communicate with a serial UART through a USB port.

You are supposed to get the configuration like this (From Sparkfun).

Configuration on Simblee App

However, what if you would like to display the configuration of RN52 on Simblee App through RFD77101, the process will be different. Here is the simple sketch of this project. FTDI chip is connected to RFD77101 using UART (RX is 25 pin & TX is 23 pin as a default), and by connecting RFD77101 and RN52 using GPIO17 & GPIO19 as RX & TX), you could do the serial communication between these chips.

Source Code



This is the UI on Simblee App.

When SMD mode started (GPIO9 pin shorted to GND).

When a command “D” was input in field1. However, I was supposed to get more than 68 bytes (As you can see, when you do the normal configuration on Terminal, the number of characters is more than 68 characters.) I need to study more about how to use a buffer, and fix this problem.

When a command that does not exist was input.

There are a lot of available commands that you can see. This project succeeded! Thanks.


Multiple LiPo Batteries Charger with a micro USB connector

After I received the acceptance of Maker Faire Bay Area 2018, I had to prepare a multiple lipo batteries charger because in Maker Faire Bay Area 2017, I had five lipo batteries and a lipo battery charger with a micro USB connector, but lipo batteries were dead faster than I expected, and only one lipo battery charger could not cover all dying lipo batteries. Therefore, I decided to make my own lipo charger rather than buying one.


These are the parts that I used for a PCB. The total cost for a multiple lipo batteries charger with a micro USB connector was only $11, so it must be cheaper than other products you can buy in online store.


This is the schematic that I designed. It was based on the Sparkfun lipo battery charger, but it could become multiple lipo batteries charger by connecting a micro USB and IC chips for lipo charge management control as a parallel circuit. When I tested how much voltage was supplied to each branch by a multimeter before I soldered all parts, around 5v was supplied from a micro USB connector, so it theoretically worked!


This is the PCB layout that I designed.


In this test, I wanted to check if LEDs were correctly turned off when one of these lipo batteries or all lipo batteries were fully charged. Initially, all lipo batteries were not charged.

After a couple of hours, all batteries were fully charged, and LEDs were also turned off correctly!!!

This project was completed!

My Progress of PCB Layout

It has been six months since I started doing Schematic design and PCB Layout by myself. I have been working on these things for improving my engineering skills and exhibiting my prototypes in Maker Faire, especially for bone conduction devices that I am developing. I finally could make my own PCB which worked perfectly, so I will show my progress of PCBs.

The first experiment failed…

When I developed my own PCB for the first time, I designed a schematic which was definitely over-skilled for me. Even thought I just wanted to make a PCB which can make sounds through an amplifier, I put BLE for Bluetooth function, and Li-Polymer Charge Management Controller to charge a LiPo Battery. Of course, the PCB did not work because I did not know how to design schematics and PCBs. What I learned from this failure is…

  1. Do not try to design a complicated PCB for the first time.
  2. Increase the difficulty of schematic and PCB layout gradually.
  3. Know how the electronics work better than anybody else.

The second experiment also failed…

From the first failure, I design a easy PC board by eliminating a lot of functions that I was not supposed to use this experiment. And, this is the schematic that I designed.

However, this schematic also did not work because It had three errors.

  1. I did not connect Pin 21 (Thermal Pad) on an amplifier to the GND (ground).
  2. R1, R2, and R3 (resistors) were not working as pull-up resistors.
  3. INL- (Left channel negative audio input) and INR- (Right channel negative audio input) also did not connect to the GND.

In order to fix these errors,

  1. Make a hole on pin 21 using laser cutter and solder pin 21 to GND pin using a tiny wire. (The reason why I made a hole was the package of the amplifier was QFN and needed to be soldered using soldering cream and heat gun).
  2. Connect SDA, SCL, SDZ pins to VDD pin using three jumper wires.
  3. Connect INL- to GND pin using a jumper wire.

After these debugging, my PCB called BCv2.0 finally worked.

BCv2.1 came out!

From previous failure, I redesigned the schematic.

The PCB became much smaller and practical and I removed the external 3.5mm headphone jack and used SMD headphone jack.

By placing components on both side, I could minimize the size a lot.

The Size Comparison

I could successfully minimize the size of PCB. This is the comparison of BCv2.0 (Green), BCv2.1 (Black), and 5 cent coin.

Next challenge I will do is to put more functions such as bluetooth on my own PC Board! See you at next post!

New Bone Conduction glasses 2.1 in San Jose Mini Maker Faire

I have been thinking how I could minimize the size of my prototype and maximize the effect of it. Then, what I came up with was to make my previous bone conduction glasses to the attachable type. Fortunately, there was upcoming maker faire in 9/3/2017 after I came up with this idea so I had a chance to see people’s reactions to my new prototype. 

Fusion 360

In order to make attachable device, I needed 3d printer and some skills of 3d modeling. What I have done was to attach an amplifier PCB (middle), a battery connecter (left) and 3.5 headphone jack (right) on the top side by measuring each PCBs and calculating each positions. Of course, I could not make it only once. I failed to print a couple of times, and I remeasured, recalculated, redesigned, and reprinted many times until it fitted.

On the bottom side was very simple. It just attaches a bone conduction transducer.

In this San Jose Mini Maker Faire, I exhibited two types of my prototypes which are the bone conduction glasses and attachable bone conduction device. I wanted to get any feedback from people.

Previos prototype


New prototype


My Booth

Many people came the booth I was exhibiting my bone conduction devices, and many people told me that these were awesome. Some of them who really were into these took my business card, so these reaction of people and actions really really made me happy like I was grad to make this!

Advantage and Disadvantage of the attachable bone conduction device

These are what I realized and got feedback from people during the Maker Faire.


  • It can attach almost any types of glasses, so the users do not have to buy the glasses itself.
  • It is lighter.


  • It can not make a balance. Either side is heavier.
  • Looks uncool.


Next Step

I cannot tell you the detail but I am currently working on my own PCB to make device itself as lighter as I can. See you in next Maker Faire.

Bone Conduction Glasses 2.0 in Maker Faire Bay Area


Bone Conduction

After testing bone conduction headphone 1.0, I had an issue which the device itself was not stable on user’s head because of the shape that I designed in Fusion 360. However, I got a hint from one of my friend. Why do not you put your prototype onto glasses? I was shocked at what I have not even thought of such a simple solution. After all, I started working on new project called Bone Conduction Sunglasses 2.0. While I am soldering new thing, one of my teachers of electrical engineering recommended me to exhibit my prototype in Maker Faire Bay Area 2017.


I did not expect the prototype accepted, but I got accepted! Therefore, I would be able to introduce my prototype in public. Thank you for everyone involved it, and Maker Faire!



There are two transducers which generate some vibrations based on the audio input from 3.5mm headphone jack.



Basically, these transducers that I am using on the bone conduction sunglasses are called surface transducers. What the surface transducers do is to vibrate any object to make sounds. As you can see on this video, sounds go outside. This is something I need to fix for next prototype.

In Maker Faire

There was a faire for makers from May 19 to 21. I also exhibit my bone conduction sunglasses in my booth. I had a desktop to explain what bone conduction is and how it works with an image.


While I was exhibiting my prototype, I met 9 deaf people. These people gave me really good feedback after they tried. In addition, I got 10 times better result than I expected. Here is the result that I got through the Maker Faire. 8 of them could hear sounds through my device. One man who had an issue of Cochlea could not hear sounds. What I got from them is sounds through the bone conduction was better than some hearing aids that they are using.


After all, I have come up with an idea to next step. I might be able to exhibit the Bone Conduction 2.1 in upcoming mini Maker Faire in San Jose. See you there!