DEC PDP 11 / 24 CPU CARD: State of the art design from 1979


DEC PDP 11/24 CPU card teardown from Electronupdate:

This is a cpu card from a class of computers known as mini-computers.
By the late 1970’s DEC was about to be eclipsed by the microcomputer. At the same time this card was in production the 68000 and 8086 16-bit class micro processors were also in the market: their superior cost would soon take much of DEC’s low end market.
The card uses their FONZ-11 LSI chip set. Most interestingly the CPU instructions are micro-coded and placed into separate chips: the instruction set could be expanded at will by adding more “303E”s. Typically this would be for a floating-point instruction set.

More details at Electronupdate blog.

Check out the video after the break.

Automatic fan controller for server racks


Dilshan Jayakody published a new build:

In this post we describe fan controller which we designed for our 9U wall mount server cabinet. This fan controller is designed to drive a 12V DC cooler fan with pre-configured intervals or by monitoring the temperature of the server cabinet.
Core components of this fan controller is CD4060 binary counter, LM35 temperature sensor and LM358 operational amplifier. In this design CD4060 is used as long duration timer and it can configured to trigger cooler fan from 1-minute and up to 4-hour.

See the full post on his blog here.

Negative impedance converters


An article discusses the negative resistance and negative impedance converter from Analog Zoo:

“Negative resistance” may seem like a purely academic concept, but can be easily realized in practice with a handful of common components. By adding a single resistor to a standard non-inverting op amp circuit, we can create a negative impedance converter, which has applications in load cancellation, oscillator circuits, and more.

More details at

Check out the video after the break.

Why electrolytic capacitors are actually kinda shitty


Afroman writes, “Electrolytic capacitors are common, but knowledge of their limitations is uncommon. A demonstration is shown highlighting the difference in performance between electrolytic and ceramic capacitors in power supplies. Other topics discussed in the video: Electrolytic capacitor construction, ceramic capacitors, ESR, ESL, impedance curves, why “0.1uF”, and more.”

Via Afrotechmods.

Check out the video after the break.

Alexa (Echo) with ESP32 and ESP8266 – Voice controlled relay


Rui Santos writes, “In this project, you’re going to learn how to control the ESP8266 or the ESP32 with voice commands using Alexa (Amazon Echo Dot). As an example, we’ll control two 12V lamps connected to a relay module. We’ll also add two 433 MHz RF wall panel switches to physically control the lamps.”

More info at

Check out the video after the break.

Reading a VGA monitor’s configuration data with I2C and a PocketBeagle


Ken Shirriff wrote an article showing how to read the monitor’s config data using the I2C protocol and a board with an I2C port:

Have you ever wondered how your computer knows all the characteristics of your monitor— the supported resolutions, the model, and even the serial number? Most monitors use a system called DDC to communicate this information to the computer.1 This information is transmitted using the I2C communication protocol—a protocol also popular for connecting hobbyist devices. In this post, I look inside a VGA monitor cable, use a tiny PocketBeagle (a single-board computer in the BeagleBone family) to read the I2C data from an LCD monitor, and then analyze this data.

More details at Ken Shirriff’s blog.

Curiosity Mars Rover


The Curiosity Mars Rover project from Beatty Robotics:

We are excited to share our latest and most ambitious robot, the Curiosity Mars Rover. This is a highly-interactive, 1/10th scale functional replica of the NASA Curiosity Mars Rover. This project was ambitious for us in two main ways: First, we worked very hard to make the robot visually accurate to the original NASA rover. This necessitated custom designing and manufacturing nearly every visible component on the robot. One of the key challenges was to get the required level of detail and functionality into such a small scale robot. Second, we encapsulated all the features and capabilities we wanted for this robot into a robust, maintainable, and modular electronics package based on a stack of custom Printed Circuit Boards (PCB) that we designed. This post focuses on the external view of the robot while future posts will focus on the electronics and functionality.

More details at Beatty Robotics blog.

STM32F103 vs GD32F103 round 3: UART


Here’s the part 3 of Sjaak’s post comparing the GD32 to the STM32:

Since the GD32F103 can run as fast as 108MHz but has not a proper USB clock divider to provide a 48MHz clock for USB communication we need another way to communicate with the outside world. Since the early days of computing the easiest way to go is a asynchronous serial interface using the UART peripheral. I can try to explain how this protocol works, but here is a better write-up.

If you missed part 1 and part 2, be sure to check it out.

More info at

App note: Enable pin operation and functions of eFuses


Get to know a number of useful usage of the enable pin of ON Semiconductor’s eFuse. Link here (PDF)

ON Semiconductor electronic fuses (eFuses) are analog integrated circuits that are used to protect circuits operating from 3.3, 5, or 12 V DC supplies. They have numerous protection functionalities such as overvoltage clamping, current limiting, thermal shutdown, and a controlled output voltage slew rate. They are available in thermal latching or thermal auto-retry configurations.

A key feature of the eFuse family is the enable pin. This application note describes the features of the enable pin and provides guidance to ensure its proper use. The enable pin of any eFuse may be left floating if the application does not require that it be controlled and does not require thermal fault notification.

App note: eFuse load current measurement


App note from ON Semiconductor on eFuse current measurement. Link here (PDF)

This application note describes the load current measurement solution for the eFuses which do not provide load current monitoring feature. Since almost all of the eFuses provide adjustable current limit functionality by utilizing an external current limiting resistor between “ILIM” and “SRC” pins, it is possible to connect a current sense amplifier across that resistor and measure the voltage drop across it which would be proportional to the load current. This method mainly requires a current sense amplifier and allows user to measure the system load current without introducing any additional resistance in series with the load path.