Limiting current into an LED is very important. An LED behaves very differently to a resistor in circuit. Resistors behave linearly according to Ohm’s law: V = IR. For example, increase the voltage across a resistor, the current will increase proportionally, as long as the resistor’s value stays the same. Simple enough. LEDs do not behave in this way. They behave as a diode with a characteristic I-V curve that is different than a resistor.
For example, there is a specification for diodes called the characteristic (or recommended) forward voltage (usually between 1.5-4V for LEDs). You must reach the characteristic forward voltage to turn ‘on’ the diode or LED, but as you exceed the characteristic forward voltage, the LED’s resistance quickly drops off. Therefore, the LED will begin to draw a bunch of current and in some cases, burn out. A resistor is used in series with the LED to keep the current at a specific level called the characteristic (or recommended) forward current.
Microcontrollers are a ton of fun. Once I got hooked, there was no
turning back. Initially playing with sensors and LCDs, I quickly discovered the limits to what a microcontroller could control. A microcontroller’s GPIO (general purpose input/output) pins cannot handle higher power requirements. An LED was easy enough, but large power items such as light bulbs, toaster ovens, and blenders required more sneaky circuitry. Something sneaky called a relay:
In this tutorial we will discuss a small relay board to control the power to a normal AC outlet using 5VDC control.
All the usual warnings apply: Main voltage (120VAC or 220VAC) can kill you.
This project, done incorrectly, could certainly burn down your house. Do not work on or solder to any part of a project while it is plugged into the wall – just unplug it!
More and more these days, I am meeting people who have built complex, impressive, and clever electronic projects, and, when I ask, I’m surprised to find out that they have no formal engineering or technical education. Now, I’m not surprised because I don’t believe that electronics can’t be learned outside of a university, a good deal of my job is to try to teachelectronics outside a university. I’m surprised because, more often than not, this impressive project will include a design element, component, or concept that I doubt I ever would have been exposed to had I not attended college. How do people learn a complex subject, like say, fourth-order filters, on their own time? I am always blown away by the fact that people have mastered concepts, on their own, that I had never even heard of, let alone attempted to study, before I had the dreadful feeling of finding out that it was one of my required college courses.
Where are these people getting this information?! How did they manage to find such a (sometimes) very dry subject and keep themselves engaged long enough to master it? I ask these questions because I’m jealous. I’m jealous of artists and designers that were exposed to this field at a young age. I’m especially jealous of those lucky people who manage to find just the right book, or mentor, or resource to teach them and keep them engaged in a subject that, in college, I paid a boatload of money for someone to teach me. Continue reading
When it comes to grafting electronics onto skin, John Rogers from the University of Illinois at Urbana-Champaign churns out epidermic tech at a seemingly fevered pitch. Perhaps his latest creation will make sure he doesn’t overheat.
Along with a team of researchers from the U.S., China, and Singapore, Rogers has designed an extremely pliable patch that, when applied to the skin, can accurately measure skin temperatureand Continue reading
Why use a relay with an Arduino board?
Individual applications will vary, but in short – a relay allows our relatively low voltage Arduino to easily control higher power circuits. A relay accomplishes this by using the 5V outputted from an Arduino pin to energize an electromagnet which in turn closes an internal, physical switch attached to the aforementioned higher power circuit. You can actually hear the switch *click* closed on even small relays – just like the big ones on street corners used for traffic signals. Continue reading
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
At the end of this instructable you will be able to detect your car as it approaches the wall inside your garage, signalling you that the car is inside far enough so you can close the door.
Most car sensors will use a microprocessor to help calculate the distance of an approaching car when entering the garage.
The main component and the challenge was to use a 555 timer as the driving “brains” of the project. So here we go: Continue reading
Lets now start of with a new series – “Hobby DIY Electronics” which contains small projects to start for beginners, robotics and much more. Enjoy the series of upcoming posts and do leave your experiences and messages in the comments section below.
Making Bibberbeests with kids is a HUGE success at schools, parties and festivals
Now what is more fun than a Bibberbeest? A remote controlled bibberbeest, using a standard audio/video RC?
So what I needed was a receiver circuit for a standard TV RC that can switch on and off a Bibberbeest’s motor, working on 3 Volts max.
At first I was tempted to go the microcontroller way, But in my eternal search to keep things simple, I eventually decided to use a hardware-only circuit: Just eight parts on a 2,5 x 4 cm board (1″ x 1,5″).
After some trial and error I used this IR toggle switch diagram (with slight mods) around a 555 timer chip by member BIC, which works quite well.
Step 1: Tools and materials
Recently I wanted to replace a rechargeable battery pack from a RC car. I tried getting a rechargeable battery pack similar to the original one but that didn’t last even half the period the original one had lasted. So I had to find out an economical way of getting batteries replaced.
Instead of taking a chance on another unreliable replacement battery pack, I decided to look inside the existing one. The plastic shell consists of two parts held together with transparent tape that is easily removed with a razor blade. Inside, there are three industrial tabbed cells of the same length and diameter of consumer AAA cells, without the bump on the positive terminal.
Given the identical cell size, it distresses me that the manufacturer didn’t simply mold a AAA battery holder into the handset. This consumer-friendly feature would have allowed the end user to replace the individual cells using off-the-shelf consumer batteries. The idealist assumes this is a safety feature to prevent errant installation of alkaline cells or mixed chemistries that might catch on fire when recharged from the base. Continue reading