Sandwich, the Line-Following Robot
This is a simple, yet sleek, line-following robot that you can reproduce in your home laboratory. A racetrack movie appears at the end of the page.

Printed Circuit Board for Sandwich
Stuffing instructions for a professional, double-sided, printed circuit board for Sandwich. The board has silkscreened part numbers and a solder mask, making it a fast, easy, and reliable way to build.

Jet, the Ultra-Fast Line-Following Robot
Learn the technical extravagance that competition leads to, as a line-following robot breaks the 100 cm/s barrier. Includes plenty of techno-babble and names of people you don't know.

Sweet! The Line-Following Robot
An m&m's candy container provides a fun body for a smart line-following robot. Videos show the auto-contrast, dark-or-light detection capabilities. Sharp turns and crossovers don't slow this car down, but it can automatically stop at the end of the line.

No.2 Mini-Sumo Robot
Pictures and videos of a champion mini-sumo robot that defeats opponents with pencils (yes, seriously). The robot has a 360-degree infrared opponent detection system and large LEGO wheels with embedded motors.

Bugdozer Autonomous Mini-Sumo Robot
Based on an MC68HC908GP32 microcontroller, this pulse-width modulated 18-volt dc scoop-on-wheels saw combat in November 2000. Using two 38-kilohertz infrared sensors and 4-front/1-rear near-red phototransistors, Bugdozer tries to push opponents out of the ring while staying within the white borders herself.

Illustrated Guide and Rules for American Robot Sumo
Robot Sumo is a simple, but fun, pushing contest. This guide is a complete description and walkthrough of a Sumo robot contest. It includes a variety of regulations, as well as tips and suggestions.

Mini-Sumo Robot Ring
A mini-Sumo ring is small, lightweight, and can be transported in a car. Having your own personal ring gives your robots the advantage of plenty of practice and experimentation. It's easy to build a competition-quality ring when you know the tricks.

XS Boost, Chef's Salad Solar Robot
Includes some unusual parts, such as N-size cells, tilt switches, and a finger-friendly dipswitch. It has a very efficient solar engine that uses a Maxim voltage doubler chip to power Maxon motors. As such, this robot runs constantly in moderate sun (no pauses between bursts).

Appetizer Robot
This solar-powered robot is built with a BEAM design. Small dc motors are driven by a capacitor and steered by photodiodes. Photographs, links, a video, and a schematic are provided.

Bipolar Transistor H-Bridge Motor Driver
For battery-powered (low voltage, low current) motor operation, the classic discrete-transistor bipolar H-bridge beats most MOSFET and prepackaged motor driver chips for most hobbyists. But, are some of the newer transistors better in this well-known hbridge design over the common 2222, 2907, 3904, or 3906 TO-92 transistors?

Pulse-Width Modulation (PWM) for Motors and LED Displays
Variable duty-cycle PWM is a great method for controlling the speed of a DC motor and the brightness of an LED display. You can make a simple PWM circuit (without a microcontroller) by using off-the-shelf electronic parts such as an inverter chip, diodes, a capacitor, and a potentiometer.

Mounting Motors and Attaching Wheels
Three different ways of connecting wheels to motors and securing motors to robot platforms. Includes drilling a pair of glued LEGO bricks, a solid UHMW coupler rod, creating motor mounts from aluminum angle stock, and a v-groove belt pulley system.

Faulhaber Gearmotor with Encoder and Right-Angle Shaft
A number of surplus sites are selling a compact, low-current motor that is perfect for robotics. The 6V motor includes a 141:1 gearhead, a magnetic quadrature encoder, and a 90-degree output shaft.

H-Bridge Motor Driver
A wiring diagram, photograph, and movie of an H-bridge dc motor driver circuit implemented with a TC4424A, TC4427A, or MAX4427 dual MOSFET driver IC. Very useful for running small bot gear motors.

Motor Mount Clamp Block
Sometimes, a small electric motor will lack mounting screw holes. Other times, a robot or device needs several things tied to the motor mount. A simple slitted block with screws can securely hold a motor in ways that other mounts cannot.

An Aluminum LEGO Hub Made on a Mill
Because LEGO tires, gears, and axles are great for building robots, I keep coming up with new adapters to connect them to standard motors. This latest method applies to the LEGO wheels that don't have cross-axle holes. Couplers and hubs are best made on a lathe, but this shows that you can create miniature round parts on a mill.

Making a Lego Wheel to Gearhead Motor Coupler on a Lathe
Lego has some fantastic wheels to use on robots. But, Lego doesn't have a wide selection of motors. Here's how you can machine an adapter on a lathe to use Lego tires with off-the-shelf gearhead motors.

Tiny Motors
Miniature motors are wonderful for B.E.A.M. robots or moving small loads. A plentiful source of inexpensive commercial motors are those used as vibrating alerts in pagers and cell phones. But how does one remove the metal offset weight?

Machining Parts for Friends
Machining a child safety gate clamp, a bolted bracket for a satellite radio, a LEGO shaft motor coupler, a compression tube nut, vise jaws for holding PCBs, and a brass lathe carriage lock.

Making a Brass Face Plate and Brass Pushbuttons
Machining solid brass stock on a milling machine to make an attractive front panel for an electronic project. Also, machining brass rod on a lathe to make flanged buttons.

Soda Pop Top Cleaner
Have you ever received an aluminum can with gunk in the groove on the top? Ick! Gross! This device is intended to push a paper towel firmly into the unreachable crevices, so that the can can be cleaned with a simple twist. The article describes using a wax mold to determine the proper dimensions and using the compound on the lathe to cut the angle.

Low-Cost Tips to Prevent Rust in Your Home Machine Shop
Plastic containers, cut-to-length tubing, and silica gel packets are inexpensive ways to protect your drill bits, end mills, metal taps, and other cutting tools against damage from rust and tool-to-tool contact. However, a dehumidifier may not be the best approach.

Caliper Capacitor
To avoid replacing batteries, attach a device to an external power source. But, that can result in operational problems due to electrical noise. Adding a capacitor to the battery compartment can fix that. See an example where an LR44 battery is replaced in a digital caliper.

Straightening Screws, Bolts, or Rods
In the event that a bent part can't be replaced, here is a technique for fixing a bent piece by carefully applying torque with a steel pipe while the part is held in a vise.

Testing Materials for Infrared Transparency using a Remote Control
Most robot light sensors are infrared (IR) based. As such, what they see may be very different than what you see in visible light. Here are some simple tests that you can perform on materials using a remote control to determine if the material is opaque or transparent to infrared.

Bonus: David attempts to paint plastic to see if more IR can be blocked.

Testing the Sharp GP2D12 Infrared Distance Measurement Sensor
How to create a distance measurement system using an inexpensive level, a bracket, and slide. Oscilloscope traces show why a capacitor is required for this sensor.

Polarized Light Beacons and Photosensors
Linear polarizing filters can be placed over light sources to act as beacons. By placing a pair of orthogonally-oriented polarized films over ordinary photosensors, the robot can distinguish between two different beacons. This can be useful for robot contests or for navigating between a destination and a charging station.

38-kHz Infrared Emitter Revisited
Infrared LEDs are commonly used for object detection in robots. Blinking the LED on and off 38,000 times a second improves long-range detection and reduces false triggers. Pictures, comparisons, and a schematic demonstrate a simple, reliable, low-power 555 CMOS circuit.

Cadmium-Sulfide Photocell Grab Bag
Nine different kinds of photocells from a grab bag. Some were defective. But the variety of sizes is nice to have.

Color Sensor for Robot
I experimented with developing a simple, active, color, object sensor for my robots based on three ultra-bright LEDs or a single RGB LED. An old-fashioned cadmium-sulfide sensor or modern TAOS light-to-voltage converter detects the brightness of the reflected red, green, and blue as each is turned on individually.

Reverse an LED to Make a Color Photosensor
Surprisingly, if you put an LED in backwards and amplify the signal with an op amp, you can create a color sensor as though the LED were a photodiode. This article shows how to improve the signal quality with multiple LEDs, provides tips on reducing electrical noise, show how to convert the output to a digital signal, and includes a schematic and breadboard photo to help you implement the circuit.

Electronic Counter and Quadrature Encoder Reader
The counter can read one or two digital or analog sensors and display the running total on an organic LED display. The counter controls the speed of an attached DC motor and can stop it when a certain count is reached. The project features a continuous rotation rotary encoder dial, with a cut-away view and an explanation of how quadrature encoding works. Finally, there is an in-depth example of why interrupts are better than polling.

Optical Encoder with Digital Quadrature Output
Quadrature encoders use a pair of photosensors to detect the rotations of an optical target disc. A digital output produces a clean square wave that a robot microcontroller can use to determine motor speed and motor rotational direction. This particular encoder uses red LEDs rather than infrared to make it easier to aim and debug. The article includes oscilloscope traces and the circuit laid out on a solderless breadboard.

Mini-Mill Digital Tachometer
Hobbyists have to experiment with speeds and feeds to get optimum cutting rates and surface smoothness without tool breakage. An RPM display is necessary to take advantage of existing tool rotation rate charts, but the Microlux milling machine doesn't have such a readout. Here's how I made mine with almost no modification to the existing mill. Yes, it's yet another tach project.

Combination Handheld Tachometer, Thermometer, and Counter
Inspired by the need to measure dc motor speed and detect overheating, this 68HC908KX8 microcontroller-based circuit displays various statistics on six-digit, eight-segment, numeric LEDs. See movies of a thermister in action as well as a reflective or interrupt-based photosensor counting.

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.

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.

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.

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.

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.

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.

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.

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.

Debounced Counter
A break-before-make double-throw switch is debounced by a NAND SR latch. The signal is fed into a decade counter and a LED decoder driver. If you don't know what that means (and you'd rather not use a microcontroller) then read this article.

Alphanumeric LED Display Project
A phenomenal 256-diode ROM acts as a character generator for a two-digit hexadecimal display.

Homemade Printed Circuit Board
Making a custom printed circuit board (PCB) takes some setup time and supplies, but is well worth the repeatable, reliable results. The example board is single-sided copper with through-hole components. Two-sided and surface-mount circuit boards follow.

Erasing PCB Tarnish with a Pencil Eraser
Microscope images of pads and holes on a printed circuit board after being rubbed with various types of erasers, a buffing wheel, and Scotch Brite scour pads. This is a simple method for removing oxides from PCB plating and electronic part pins prior to soldering.

Microscopic Views of a Printed Circuit Board
Photographs of homemade circuit boards under 10x, 60x, and 200x magnification using the Intel QX3+ microscope. Shows details of pixel aliasing, copper cracks, poor resist transfer, and soiling from sticky flux paste.

Do-It-Yourself Video Inspection Microscope
There are times when a small magnifying glass is inadequate -- such as sorting a lot of small parts or inspecting a batch of circuit boards. You can use a consumer video camera and a monitor to get a close-up view for a lot less money than buying a special tool. This article also includes a tip about using a rare-earth neodymium magnet for collecting SMD parts.

Repairs and Improvements
Visit Sweet, Roundabout, Hard2C, and Chicago for a weekend of simple fixes for line following, mini sumo, and solar power. See how different types of screws can help a robot slide, hide, and hold onto a gear.

Inside the Big Trak
Ever wonder how the Big Trak toy worked? And what about the mysterious IN button on the keypad?

Digital Number Systems
Whether you're working on robots, digital circuits, software, or microcontrollers, you'll encounter numbers that aren't decimal. This tells you how to convert a number to and from hexadecimal, binary, octal, and decimal.

Roundabout
This is an all-in-one intermediate-level robot that can explore rooms, avoid obstacles, follow lines, and compete in mini sumo (see the movies). The robot can be made in a variety of body styles with either a logic chip or microcontroller brain.

Roundabout PCBs
Instructions and tips for assembling Roundabout's electronics using the templates or ready-made PCBs available online.

Controlling a Robot with an Atari Joystick
Every once in a while, a project turns out really well. This is one of my favorites. Using a classic Atari or Commodore joystick, you can make a simple circuit to control a robot or other electronic device. Includes a schematic that does not require a microcontroller or even a voltage regulator. Also discussed is how to modify a Solarbotics GM7 motor for easy mounting to a Lego Technic frame.

Robotic Kill-Switch Target
Mounting a robot's power switch in the front adds a new method of defeating an opponent in robot combat. Rather than sustaining major damage, the robot can be disabled by hitting the snap-action switch. Schematic and photographs included.

Wireless Video and Speech Telepresence Robot
Movies, photographs, tips, and instructions for a remote-controlled semi-autonomous wireless robot that navigates with dead-reckoning from Maxon motor encoders. The motherboard includes an Atmel ATmega644 microcontroller, four Infineon TLE-5206-2 motor drivers, Panasonic IR remote receiver, and I2C communication. The robot also includes a Devantech speech module.