Tag Archives: James Hobson

Measuring capacitance

 with an Arduino Uno

Capacitance is typically defined as the ability of a body to store an electrical charge. More specifically, any object that can be electrically charged exhibits capacitance.

 A multimeter or multitester, also know as a VOM (Volt-Ohm Meter) can be used to measure the capacitance of a capacitor, but what if you don’t have one handy?

As it turns out, capacitance can be measured with an Atmel-based Arduino Uno (ATmega328) – sans external components and only ~20 lines of code. 

A blog post, written by Jonathan Nethercott that was recently featured on HackADay, explains how.

“[He] does an excellent job explaining a capacitance test circuit which uses a reference capacitor to calculate the unknown capacitance,” writes HackADay’s James Hobson. 

”He further explains that, with the Arduino Uno, you can remove the reference capacitor from the circuit, and simply use the stray capacitance present in the board and microcontroller, which can be calculated.”

Meaning, creating a test circuit is as simple as plugging in a capacitor to pins A0 and A2. On the software side, Nethercott’s code sense a 5V pulse to the capacitor – measuring the voltage on the other side, looping every half second and outputting the data onto a chart.

Nevertheless, as HackADay’s Hobson notes, the above-mentioned technique does require some calibration, with Jonathan measuring a known capacitor for a baseline and using the confirmed data to calculate the stray capacitance in the Arduino. 

Once accurately calibrated, users can typically achieve a resolution of approximately 1% for capacitors between 3.5pF and 225pF and around 5% for capacitors between 0.5pF and 1300pF.

Interested in learning more about how you can macgyver your Arduino Uno to measure capacitance? You can check out Jonathan Nethercott’s detailed blog post here.

A retro modern Nixie clock with Atmel’s ATmega48

As we’ve previously discussed on Bits & Pieces, there really is nothing quite like the comforting glow of a Nixie tube. Reboots apparently couldn’t agree more, as the retro modern Nixie clock he designed clearly illustrates.

According to HackADay’s James Hobson, Reboots was inspired to build the clock after coming across an old General Electric battery charger for sale.

“The Nixie tubes he chose for the project came from a lot sale on eBay, Russian surplus IN-12 tubes. He even managed to find an English datasheet for them,” Hobson explained.

“Having decided on the Nixie tube, driver, and case, he now needed a reliable power supply. Threeneuron’s design fit the bill nicely, however it ended up being a bit noisy under load, but the TubeClock kit used a free-running transistor oscillator, which was in fact even louder under load.”

From there, said Hobson, it was a matter of testing the tubes, prototyping PCBs and programming Atmel’s stalwart ATmega48 microcontroller (MCU) for the task.

Interested in learning more about the retro modern Nixie clock? You can check out the project’s official page loaded with additional images here.

Previous Nixie-based projects featured on Bits & Pieces include “The ATtiny1634 Nixie clock,”  “Building an Arduino-powered Enigma machine,” and “Atmel’s ATmega645P goes tick tock.”

Arduino Uno powers this Game of Life clock

The Game of Life (aka Life) can best be described as a cellular automaton created by the British mathematician John Horton Conway in 1970. Essentially, it is a zero-player game, meaning that its very evolution is determined by an initial state, requiring no further input. Simply put, an individual interacts with the Game of Life by creating an initial configuration and observing how it evolves.

The game made its first public appearance in the October 1970 issue of Scientific American, having been featured in Martin Gardner’s “Mathematical Games” column. As Wikipedia notes, the game is rather interesting from a theoretical point of view, as it has the power of a universal Turing machine, namely anything that can be computed algorithmically can be computed within Conway’s Game of Life.

Recently, a Maker by the name of Matthews created a Game of Life style clock. According to HackADay’s James Hobson, Matthews was originally inspired by another Game of Life Clock featured on HackADay a few months ago, although he did implement a number of critical changes.

”First, Matthews wanted a much bigger playing field, so he found a 16×32 RGB LED matrix. Second, he wanted the time to always be visible so it actually works as a functional clock,” Hobson explained.

“At the beginning of every minute starts a new Game of Life which plays over top of the time displayed. Three buttons on the top allow for many adjustments including brightness, timezone, speed, colors and even edge behavior.


The Game of Life clock is powered by an Atmel-based Arduino Uno (ATmega328) paired with a Chronodot RTC module to assist with accurate time keeping.

Interested in learning more about the Game of Life clock? You can check out the project’s official page here.

Designing an Atmel-Arduino RFID car starter

A Maker by the name of Pierre recently decided to celebrate the purchase of his first car by designing a DIY RFID electric starter.

According to the HackADay crew, an Atmel-based Arduino Nano (ATmega328) is tasked with controlling two relays which turn the car on and off.

“Instead of adding a button for ‘push to start,’ Pierre opted for a 13.56MHz RFID module,” explained HackADay’s James Hobson. “Now when he passes his RFID badge across the dash, the car turns on — if it’s held there for over a second, the car starts. Another pass and it will turn off.”

Pierre’s ultimate goal is to move the circuit closer to the wheel and use an NFC ring to start the vehicle.

Interested in learning more about starting a car with RFID tech? You may want to check out HackAday’s archived story about a Maker named Jair2K4 who actually implanted an RFID chip into his hand.

Atmel’s ATMega16 powers this hard disk clock

A Maker by the name of Martin Stromer has designed a slick Atmel-powered (ATMega16) Hard Disk Clock.

Mad props to Martin for sharing this nostalgic project with the HackADay crew and the rest of the wider world. Some of us still can’t get over the massive size of the hard drive, which appears to be well over 20 years old with a limited capacity of only a few dozen megabytes. This definitely takes us back to the golden years of ASCII art, bulletin boards (Renegade & Wildcat), door games like Solar Realms Elite, CRTs and headache-inducing CGA displays.

So how does the clock work? Well, according to HackADay’s James Hobson, the platter reads the time by rotating 30 degrees at once, per hour.

“The read-write head inches across the disc to display the minutes. Each of the black lines represents a quarter hour,” writes Hobson.

“The whole thing is controlled by an ATMega16, which maintains almost all of the original hardware. Did we mention it’s also easy to set the time? Simply rotate the disc by hand and slide the read-write head into place, then press the reset button.”

As Hobson notes, the ATMega16-powered hard disk clock illustrates how old electronic equipment such as retired HDDs can be transformed into something useful. Additional examples covered by HackADay include hard disk grinders, hard disk DJ scratch pads and even a cotton candy spinner.

Interested in learning more about the HDD clock? You can check out the project’s page here.