Is Junxiao in the Room? Presence Detection with nRF52 Bluefruit

I recently obtained some Adafruit Feather nRF52 Bluefruit LE boards. The main chip on this board is the nRF52832 from Nordic, which offers Bluetooth Low Energy (BLE) communication, but does not have WiFi. Adafruit made a nice Arduino core for nRF52, so that it can be programmed easily with the familiar Arduino environment.

Incidentally, this isn't the first BLE device I have. Many small battery-powered devices, including the Fitbit Alta HR tracker I wear daily, uses BLE for communication. This means, I could use the nRF52 board to answer one question: is Junxiao in the room?

Loud Pumpkin with Circuit Playground

It's October. Pumpkins are filling the grocery stores. This means one thing: Halloween is coming!

I'm told that I'm supposed to wear a costume on Halloween. However, I'm too broke to buy an outfit for just one day, so I'm going to wear a colorful circuit board instead. This year, I'm going to become a pumpkin. Well, sorta.

The board is an Adafruit Circuit Playground Express. It packs 10 NeoPixel LEDs that can display any color, four sensors, and a few buttons. My code uses the microphone sensor to measure how loud is the environment. Based on measured sound pressure, it then lights up a number of NeoPixels to #ff7619 the "pumpkin color".

ESP8266 Call Button

It's NDN Community Meeting again and this time I'm officially presenting HomeCam at the demo session. I'm the sole presenter of this project. Normally, I have to stay at my table to show my project to the audience. However, I don't want to miss the chance of seeing what others have been doing. To solve this dilemma, I come up with an idea: a call button.

I put a big button on my table. It is labelled as: if I'm not here, press the button to send an Interest. Then, I wear a battery powered light ring on my body. Whenever someone presses the button, it lights up for 15 seconds.

me wearing a light ring at NDNcomm demo session

How It Works

Both the button and the light ring are based on ESP8266. The light ring unit acts as WiFi access point and NDN producer. The button unit acts as WiFi station and NDN consumer. When the button is pressed, the consumer transmits a signed Interest, and the producer turns on the light for 15 seconds after verifying the signature. Since the light ring unit is battery-powered, it enters deep sleep mode if there's no connected WiFi client.


1998年,我参加小学生作文竞赛时写下了一篇《二十一世纪电视畅想》。 20年过去了,让我们来看看,这些畅想变成现实了吗?

小朋友们,你们想过没有二十一世纪的电视是怎样的呢? 我学习之余,常在潜心研究、精心设计着它们呢。我告诉大家,到那时的电视机呀,小的只有手表这么小,大的足有三层楼高。

在二十一世纪,“手表这么小”的电视机称为“智能手表”。 它们不能直接接收电视信号,而是接入移动通讯网络,通过因特网可以观看电视。

“三层楼高”的电视机在广告业已经普及。 纽约时报广场就有多幅大型电视屏幕,每天24小时播放广告:


Get Online in McDonald's with ESP8266

McDonald's used to be the largest chain of free restrooms in the world. Nowadays, they are the largest chain of free WiFi across the United States. Every McDonald's I've been to offers AT&T WiFi services. I can walk in, connect to "attwifi" on my phone, accept the license agreement, and I'm online.

attwifi captive portal in McDonald's

The license agreement page is called a captive portal, a web page displayed to newly connected users before they are granted broader access to network resource. While it's trivial to click through the captive portal on a smartphone, if you are wearing an ESP8266 as a connected jewelry, it would not connect successfully. When I encountered a captive portal in my apartment WiFi, I made an Arduino sketch to send the packets I found through Fiddler, but McDonald's WiFi is different:

  • Each McDonald's store hosts their captive portal on a different domain.
  • The form submission step needs several parameters from the HTML, but does not use cookies.

attwifi captive portal form HTML

How to Print uint64_t in Arduino

The Arduino programming language looks like C++, but it is weird in its own way: there's no C++ standard library. In C++, you can print a variable to the debug console with std::cerr << x;. In Arduino, you have to write a function call: Serial.print(x);. I love that the Streaming library brings back the familiar syntax Serial << x; through some template and macro magic. But when it comes to a uint64_t variable, nothing works!

error: call of overloaded 'print(uint64_t&)' is ambiguous

note: candidates are:
note: size_t Print::print(const __FlashStringHelper*) <near match>
note:   no known conversion for argument 1 from 'uint64_t {aka long long unsigned int}' to 'const __FlashStringHelper*'
note: size_t Print::print(const String&) <near match>
note:   no known conversion for argument 1 from 'uint64_t {aka long long unsigned int}' to 'const String&'

Simple Temperature and Humidity Indicator with ESP8266 and HTU21D Sensor

I decide to mix up a few existing toys to make a simple temperature and humidity indicator. ESP8266 reads temperature and humidity from an HTU21D sensor, and displays the numbers on a 4-digit 7-segment LED display. Since a 4-digit display isn't wide enough for both temperature and humidity, the display cycles between temperature, humidity, and a blank state.

temperature and humidity on LED display


Bill of materials

Listen to Podcasts

Apartment life involves a lot of chores: cooking, cleaning, folding laundry, etc. Many American housewives watch TV while doing chores, but I do not have a TV. The next closest thing is the radio, but I find it boring to listen to the same news over and over. In Dec 2016, as I scroll through my iPad Mini, I discovered the best activity to accompany chores: podcasts!

A podcast is a series of periodically published digital audio files that a user can download and listen to. iPad Mini comes with a Podcasts app that allows me to search for, subscribe to, download, and listen to podcasts.

My initial subscriptions include:

  • Radiolab, in-depth news stories. It's similar to a magazine, but in an audio format.

    My favorite episode is The Ceremony, a report about how Zcash generated their cryptocurrency parameters.

  • Stranglers, true crime stories about the Boston stranglers. They kept my eyes wide open at nights.

Listening to podcasts improves the quality of my housekeeping, because I do not rush through the chore so that I can switch to more "enjoyable" activities sooner. Instead, I can take my time cleaning the bedroom, while enjoying great audio content. I do have to keep it quiet, so that I can hear what's coming out of the small speaker on the iPad Mini.

Four-key Piano on Fipsy FPGA

The newest addition to's toy vault is Fipsy FPGA Breakout Board, a tiny circuit board offering a piece of Lattice MachXO2-256 field-programmable gate array (FPGA). After porting an SPI programmer to ESP32, it's time to write some Verilog! Blinky is boring, but I did it anyway. Then, I'm moving on to better stuff: a piano.

The piano is an acoustic music instrument played using a keyboard. When a key is pressed, a hammer strikes a string, causing it to resonate and produce sound at a certain frequency. A normal piano has 88 keys, and each key has a well-defined sound frequency. My "piano", built on Fipsy, has four keys, and uses a passive buzzer to produce sound.

Fipsy FPGA connected to a buzzer and a keypad

Play Tone on Passive Buzzer with FPGA

A passive buzzer plays a tone controlled by an oscillating electronic signal at the desired frequency. In Arduino, the tone() function generates a square wave of a specified frequency, which can be used to control a passive buzzer.

Program Fipsy FPGA Breakout Board from ESP32

MocoMakers is creating Fipsy FPGA Breakout Board, a tiny circuit board offering a piece of Field-programmable gate array (FPGA). I worked with FPGA years ago in class projects, but didn't have access to a device after that. I backed the project, and received two Fipsy boards on Jul 20.

Fipsy is a very simple board: there is no power regulator or USB port. The official method to program the Fipsy is through the SPI port on a Raspberry Pi. It is easy to setup, and is a good use case for my Raspberry Pi Zero W, but there is one problem: It is good practice to power off the circuit when modifying hardware wiring. However, powering off a Raspberry Pi cleanly requires sending a shutdown command and waiting for a few seconds. If I just pull the power cord, I would risk corrupting the filesystem.

ESP32 microcontroller has SPI ports, and can be powered off and restarted very quickly. Can I program Fipsy from an ESP32?

Fipsy connected to Heltec WiFi\_Kit\_32

Hardware side is easy. ESP32 has two available SPI ports, HSPI and VSPI, and I connected Fipsy to the Heltec WiFi_Kit_32's HSPI port. All that remains is deciphering the spaghetti code of the official programmer. After a day of hard work, I got it working: