Electronic Projects, Circuits, and Devices

Here are some nifty little projects that are useful for tasks in the workshop or home, as well as some that are more decorative. Some of the articles help beginners with simple circuits, whereas others delve into details on specific microcontroller chips.

Model rocket liftoff Model Rocket Launch Controller
The secrets to a successful launch controller are thick cables, power through a relay, and a beefy battery (such as a lead-acid motorcycle battery). Learn what is inside a low-end commercial rocket launcher, how to make your own simple launch controller, and take a look at a fancy rocket controller that includes covered pilot switches and a switch lock.
Rocket ignition system thumbnail Rocket Ignition System
The problem with most model rocket launch controllers is that the battery is located with the operator, far away from the launch pad. This requires thick cables and wastes significant energy. By locating the battery near the rocket engine and using a remotely-controlled relay, the improved launch system is more efficient but can still be built at home. Includes complete schematics, the pcb layout, and source/object code.
Tiny thumbnail graph of weather in Chicago Weather Station
Logging six temperatures and solar activity at one minute intervals around the clock using a 4 megabyte serial flash chip. The observation results are graphed to demonstrate weather conditions over multiple days in the Chicagoland area. Ran into some problems with a broken wire, overheating project box, shadows, and exposed sensors.
Thumbnail of a weather chart. Weather Station Charts
With the do-it-yourself weather station recording data for over six months, let’s see what can be discovered about the temperatures, sunlight, moonlight, and activities in the backyard, home office, and kitchen of a home in the suburbs of Chicago.
LED bar graph for a water softener salt-level monitor Water-Softener Brine-Tank Salt-Level Monitor
If you have hard water, did you ever forget to add salt to the water softener tank? This electronic device monitors how full the tank is using a Sharp DP2D12 infrared distance monitor. The results are displayed on a custom wall plate with a multicolor LED bar graph. The project also includes several photosensors to save power.
A ring light attached to a magnifying glass Miniature Surface-Mount LED Ring Light
Ring lights provide shadowless all-around lighting that is particularly useful for close-up work such as macro-photography and circuit-board inspection with a magnifying glass. This project also includes instructions on soldering surface-mount electronic components and machining a circuit board into a ring (round/circular/donut) shape.
Circular LED bulb thumbnail Upgrading Magnifying Desk Lamp to LEDs
Circular T9 LED bulbs are available to replace fluorescent bulbs in desk lamps. LEDs provide a broader spectrum of light, which is particularly important if you are shooting macro photographs, but is also easier on your eyes if you're soldering or inspecting boards. Unfortunately, the commercial LED bulb I received was defective and had a flickering power supply. Hacking in six additional smoothing capacitors and replacing a missing LED solved the problem.
Pumpkin with LED Candle Halloween Pumpkin with Colorful LED Candles
Extensive tutorial on putting blinking LEDs and different colored LEDs into jack-o-lanterns. Includes schematics, solderless breadboard photos, and three movies (the blue pulsing LED is my favorite). Great way of getting started in electronics! Although this was written for Halloween, the techniques are applicable for Christmas votive candles as well.
LED tester lighting up a red LED Standalone LED Tester
Description and schematic for a constant-current LED tester. It safely lights up standard through-hole and surface mount LEDs, while providing easy access to current and voltage measurements.
LED Tester Pro thumbnail LED Tester with Display
Throw away your multimeter and spreadsheets, here is a self-contained current-limited LED tester that displays LED voltage drop, current, and recommended resistor. With about $10 in parts and a 9V battery, this indispensible tool is tailored for the everyday tasks of the electronics enthusiast.
5V regulator with power indicator light thumbnail 5V Regulator Cap for 9V Battery
For quick portable projects and temporary hacks, it is often faster to reuse a simple 5V regulator circuit than to integrate a power supply into the device design. My toolbox has an LED tester and magnifier light, so why not add a convenient 5V regulator cap to the collection? There are nicer ones on the market that have surface mount components, but half the fun of an electronics hobby is creating something basic in your own style. This double-decker board with flashing LED power indicator allowed me to experiment with flush battery snaps and board interconnects.

Tiny chip regulator thumbnail Mercury Battery Replacement Regulator
Several decades ago, mercuric oxide button cells were common consumer power sources. Mercury was phased out due to environmental concerns, leaving behind vintage photographic equipment and watches that were incompatible with alkaline's wide voltage change or silver-oxide's slightly higher nominal voltage. Tinkerers have come up with a variety of solutions for many devices. Perhaps modern technology can address a few more with an itty-bitty 1.35V low-dropout linear regulator.
Temperature displayed on 4-digit multiplexed blue LED display Dual Fan Controller
A birthday present gone too far. An overengineered temperature-based automatic twin fan controller with brass face to keep a kitchen PC cool.
Toggle switch with safety cover Fighter Pilot Safety-Cover Toggle Switch
See how an illuminated toggle switch works by breaking one open and putting it back together. Most of these are automotive switches, which need 12 V. The circuit schematics on the second page of the article show you how to shift voltage levels from 12 V to 5 V, and 5 V to 12 V. A microcontroller can read the switch state and blink the LED.
Insides of a trimpot with gears Trimpots
A visual guide to breadboard-friendly trimpots (small variable resistors) that appear in nearly every hobbyist electronic project. The article features comparison pictures and part numbers of 3/8-inch and 1/4-inch square single-turn and multi-turn trimmers. Even more interesting is the cutaway close-up photographs of the inside gears and brushes of these tiny potentiometers.
Printed timmer dial thumbnail 3D Printed Trimpot Thumb Dial
Create your own colorful finger-friendly dials for common trimmer potentiometers. With a little slot that press-fits into the screwdriver slot, and a dab of emblem adhesive, these home printed dials will make your projects much easier to adjust.
ATtiny in programming socket AVR Studio 4 and the STK500
To write firmware to an Atmel AVR microcontroller, you need a computer, free AVR Studio software, a hardware interface, and a little bit of knowledge. This tutorial shows how to obtain, install, set up, and write a HEX file to an ATtiny chip using the STK500 programming board. Covers fuse bits, jumper positions, ISP frequency, and target voltage.
Two digit 7-segment numeric display showing the best trim value for a reasonably accurate internal oscillator on this particular 68HC908KX8 microcontroller chip. Trimming the Internal Clock on a KX8 Microcontroller
Example algorithms for manually or automatically tuning the oscillator on the internal clock generator of the popular MC68HC908KX8 microcontroller. Also includes batch test results and a video.
A analog light or object sensor with red and green LEDs Analog Comparison, Digital Result
Comparators are very useful for comparing two analog voltages and providing a digital result. In this case, if the light source is dim, a red LED is enabled. If the light source is bright, a green LED is enabled. However, once comparators are understood, they can be useful for driving small robots or helping a microcontroller.
A montage of images from the Lite-On multifunction LED display Multi-Segment LED Display
Lite-On LTM-Y2K19JF-03 is a surprisingly good LED display with alphanumeric, numeric, and icon LEDs. The LED module includes all driver circuitry -- no additional transistors or resistors are necessary. The article also describes how to create and edit a 14-segment alphanumeric LED font using Excel.
Async tool thumbnail Serial Communication
A very popular method of sending and receiving data between devices and computers is good old asynchronous serial communication. See traces of characters being transmitted. Learn how far timing can be off before introducing errors. Includes a table of popular crystal frequencies and baud rates, as well as machining information and a source code snippet for an automatic bps detection tool.
Logic analysis of TWI problem Atmel TWI
Explains an I2C multi-master bus issue on the Atmel AVR 8-bit microcontrollers. Shows logic analyzer traces of TWI (two-wire interface).
Alphanumeric LED Display Project thumbnail Alphanumeric LED Display Project
A phenomenal 256-diode ROM acts as a character generator for a two-digit hexadecimal display.
Infrared Transmitter Project thumbnail Infrared Transmitter Project
The heart of this project is a NAND gate turned into a 40-kHz oscillator. A simple 9-volt to 5-volt regulator circuit schematic is also included.