There are three main types of 4 digit seven segment displays to be found on the market:

• Bare displays without any driver. These come in a variety of colors and with either decimal points or clock-type display with a colon dividing two sets of two digits.
• 74HC595-based displays. Usually these displays have two daisy-chained 74HC595 shift registers and rely on the host controller to fill the serial registers and handle the multiplexing. Depending on the processor speed, this ends up being a significant overhead.
• TM1637-based displays. These displays reduce the burden on the host controller because all of the multiplexing is handled on the interface chip.

This post is about the TM1637 LED displays. The {% asset_link Datasheet_TM1637.pdf TM1637 datasheet %} is terrible, but fortunately there are several libraries for Arduino that provide a little insight into how others have managed to make this work. First things first, the communication protocol for this device is not I2C despite what vendors on Aliexpress frequently claim.

Previously, I wrote about using the ESP32 to read sensor data over I2C from the Si7021 temperature and humidity monitor. Today, I’m going to briefly take you through the process of serving this data via the web.

Description

The project plan is to connect to WiFi in STA mode, collect temperature and humidity data every 5 seconds from a Si7021 sensor via the I2C bus. We will launch a web server and whenever we have a GET/ request we’ll serve a simple web page that reports the temperature and humidity. If the URL path is /h (e.g. 192.168.1.x/h) then we’ll turn on an LED connected to GPIO 4. If the path is /l (e.g. 192.168.1.x/l) then we’ll turn off the LED. In both latter cases, we’ll also serve the same page showing the temperature and humidity.

Recently I wrote about reading Si7021 temperature and humidity data using a Raspberry Pi. Now let’s try a completely different platform, the ESP32. This is essentially a project to explore using I2C on the ESP32 platform and to understand the build process.

Project layout

Since we’re developing the Si7021 interface code as a reusable component, we need to structure our project in such a way that we can easily refer to it in our main code. Here’s how I structured this project:

One of the most infuriating UX choices on the web is the developer’s choice to open every single link in a new tab. There are a few sites I interact with, including Aliexpress, where the designers have inflicted this on the users.

Fortunately, I found a solution. The Chrome extension target="_blank"-toggler works well. When you hover over a link which would open in a new tab, it superimposes a visual signal. Now you have a choice. If you click on the link, it will open in a new tab. If you Command + Shift click,^[The ⌘ + ⇧ combination works on macOS. It is probably CONTROL + Shift on Windows, but you’ll have to check the documentation.] the link will open in the same tab. Problem solved.

The Heltec WIFI Kit 32 is an interesting little module that integrates a WiFi/MCU SoC and a small OLED display on a single board. If you want to set up the Arduino IDE to work with this device and you’re on macOS, this is for you. This particular ESP32 module has a number of impressive features: 240 MHz processor speed and 4 MB of flash memory. The onboard OLED display can be conveniently used for debugging.

Brutal piece by Adam Davidson about the pivotal role that the takedown of Michael Cohen plays in the unraveling of this disastrous presidency.

The narrative that will become widely understood is that Donald Trump did not sit atop a global empire. He was not an intuitive genius and tough guy who created billions of dollars of wealth through fearlessness. He had a small, sad operation, mostly run by his two oldest children and Michael Cohen, a lousy lawyer who barely keeps up the pretenses of lawyering and who now faces an avalanche of charges, from taxicab-backed bank fraud to money laundering and campaign-finance violations.

A brutal piece on Trump from the New York Times.

There are plenty of examples these days, from Moscow to Budapest, of how “democracies” can be manipulated to the point where they can yield only one result. This is Trump’s objective, and for it he needs a weakened Justice Department, a weakened press and an American public that will believe anything. He has had setbacks but is stubborn.

Trump’s toolkit is familiar. In it are the tools of every authoritarian brute everywhere. Americans are better than this, though.

Great Stalin - banner of friendship of the peoples of the Soviet Union!

After reading about U.S. President Donald Trump’s “Number 1 fan”, Gene Huber, I was struck by the similarities between the adoration of Trump and that of Soviet leader, Josef Stalin. Throughout his tenure as General Secretary of the Communist Part of the Soviet Union, a cult of personality developed around Stalin. He was often called Великий Сталин (Great Stalin.) Propaganda posters depicted Stalin as a benevolent steward of the needs of the people.

“Спасибо любимому Сталину - за счастливое детство!”

(Thank you dear Stalin for a happy childhood.)