Simple Solar Circuits

SolarCircuits - 09

Simple Solar Circuits:

How to get started adding solar power to your small electronics projects. Use the sun to power small solar and battery powered night lights, garden lights, and decorations for halloween.

A Simple and Cheap Dark-Detecting LED Circuit



Stupidly bright.

Here’s a simple problem: “How do you make an LED turn on when it gets dark?” You might call it the “nightlight problem,” but the same sort of question comes up in a lot of familiar situations– emergency lights, street lights, silly computer keyboard backlights, and the list goes on.

Solutions? Lots. The time-honored tradition is to use a circuit with a CdS photoresistor, sometimes called a photocell or LDR, for “light-dependent resistor.” (Circuit Example 1, Example 2.) Photoresistors are reliable and cost about $1 each, but are going away because they contain cadmium, a toxic heavy metal whose use is increasingly regulated. There are many other solutions as well. Look here for some op-amp based photodetector circuits with LED output, and check out some of the tricks used in well-designed solar garden lights, which include gems like using the solar cell itself as the sensor. (Our own solar circuit collection is here.)

In this article we show how to build a very simple– perhaps even the simplest– darkness-activated LED circuit. To our LED and battery we add just three components, which cost less than thirty cents altogether (and much less if you buy in bulk). You can build it in less than five minutes or less (much less with practice).

What can you do with such an inexpensive light-controlled LED circuit? Almost anything really. But, one fun application is to make LED throwies that turn themselves off in the daytime to save power. Throwies normally can last up to two weeks. Adding a light-level switch like this can significantly extend their lifetime.

Evil Mad Scientist Laboratories: Year 3

Evil Meggies

Happy birthday to us! Evil Mad Scientist Laboratories is now three years old.

To celebrate, we’re rounding up our most interesting projects from this past year.

Quick projects and observations:

Magnet tricks

17 cool magnet tricks


The monetary density of things

Cheap calendar 2

Cheap Perpetual Calendar

Parts Tray-14

Contact Lens Case Small Parts Tray

Simple LED Projects:

lanterns - 11

Quick, easy, temporary, and beautiful LED garden lights

RoboGames Awards (on)

RoboGames Awards

LED Ghostie

LED Ghosties for Halloween

Food Hacking:

Dry Ice Martini

The Hungry Scientist Handbook

Decoder 2

South Indian Restaurant Menu Decoder

"That's no melon!"

“That’s no melon!”

Grillin 2

Hot Dog Bun Grilling Jig

LOLHearts - 34

Improved Custom Message Hearts

Apple Pie

Now that’s an Apple Pie!

Caprese - 16

Eyeball Caprese

Fractal Snowflake Cupcakes - 24

Fractal Snowflake Cupcakes



The CandyFab 6000


Harley Sleeps

Cardboard Cat Chaise

EdgeLitCard - 49

Edge-Lit Holiday Cards

Hex Boxes5

Hexagonal Stacking Boxes

frabjous - 01

Making a Frabjous

Electronics Projects

Interactive LED Dining table

Interactive LED Dining Table Circuit

Color distortion

Giant seven segment displays

DarkPumpkin - 11

Dark detecting jack-o’-lantern

SolarCircuits - 06

Simple Solar Circuits

Soft Circuit Merit Badge14

Soft Circuit Merit Badge

Kit Projects

Meggy Rainbow

Meggy Jr RGB

VideoPeggy - 09

Video Peggy in action

Peggy 2 RGB

Peggy 2 RGB

2313Card - 1

ATtiny2313 breakout boards


Revised ATmegaXX8 boards

Crafty Projects

d12 Bag

DIY d12 Handbag (of Holding)

Meggy Jr RGB Cozy-21

Meggy Cozy

no-sew iPhone cozy14

No-sew iPhone Cozy

fabric klein bottle

Fabric Klein Bottle

Seat recovery

Reupholstery with Used Denim

Missile Command Skirt 24

Missile Command Circle Skirt

Fishbowl cat quilt29

Fishbowl Cat Quilt


Turning Mollie into Maulie

Bicycle lunch bag

Bicycle Frame Lunch Bag

Acrylic Nesting Bracelets-1

Sinusoidal Bracelet Design

Microcontroller Projects

Time exposure

Tennis for Two, a video game from 1958

stockpumpkin - 11

Scariest Jack-o’-Lantern of 2008

mignonette - 09

70 bits of gaming goodness

Serial Port Added

AVR Serial Communication

lissajous-dark - 07

POV Lissajous figures

Mobius Circuit - 21

Single sided circuit board


A Bulbdial Clock

Geek Design

Snowflake generator

Vector Snowflake Application


The Amazon Kindling

Pi (squared) trivet - 9

Pi Pie Trivet

lego - 2

Lego Kitchen Crafts

Binary Birthday

Binary Birthday


Resources for getting started with AVRs

This is a short list of resources for getting started with AVR microcontrollers. It’s intended as a supplement to intro AVR classes that we have given. We intend to periodically update this list; leave your suggestions for additions in the comments, please. (Last update: September 2011)

Circuitry Snacks

555 LED flasher 1

PCB with components

Joule thief 2

Here we present what is arguably the tastiest way to design and learn about electronic circuits: make circuitry snacks!

Two of our favorite things in the world are playing with electronics and playing with food, and so it is about time that someone finally got around to combining the two. We begin by gathering up appropriate snack-food building blocks and making food-based models of electronic components. From these components, you can assemble “circuitry snacks”– edible models of functioning electronic circuits. You can make these for fun, for dessert, for your geek friends, for kids, and for teaching and learning electronics.

Make A Cylon Jack-O-Lantern

It’s a pumpkin! It’s a Jack-o-lantern! It’s an electronics project! It’s… a Cylon!

Cylons are great. They’re evil, menacing, and shiny. They have glowing red lights, computer-monotone voices, and they aim as precisely as imperial stormtroopers.

For halloween this year, we made Cylon Jack-o-lanterns in both large and small versions.
The design consists of two parts, a pumpkin-carving part and an electronics part. The big idea, of course, is to make the Cylon’s red eye scan back and forth.

How well does it work? Take a look! (Youtube)

This week’s Weekend Projects Podcast at Make Magazine is about making a programmable LED pumkin.

Our Cylon is made with a very different approach. It runs on a 9V battery and uses two cheap integrated circuits (a 555 and 4017) that together control six LEDs (or six groups of LEDs).
Circuits like this are quick, easy, and cheap to build. It’s also fun merely from the standpoint of making something that people might expect to require a microcontroller. For this particular circuit, it turns out to be cheaper and faster to do it without one.
If you’re handy with a soldering iron, you can build this circuit for less than ten dollars, in less than two hours, without any programming at all.