DanielAndrade.net

Working with LEDs and Resistors

DanielAndrade — Sat, 13 Mar 2010 14:56:57 +0000

The objective of this text is to help you to understand how Resistors work and use it in it’s most simple use, as a current limiter. If you want to know more about resistors and leds, check Here and Here.

RESISTORS:

The resistor is a passive component that is opposed to the electrical current dissipating heat, the higher the resistor value, the lower the current. This effect is called electrical resistance, while the component resistor is popularly known as resistance.

Resistance: is the property of a material to oppose the flow of electric current and dissipate power. Unit: Ω (Ohm).

Resistor: A component specifically designed to have resistance.

Utilities of resistors:

Limiting the current that flows in a circuit
Control the loading speed of a capacitor.
To make current and voltage dividers.
Transforming energy into heat (Joule effect).

When applying a voltage in a resistor, it creates a current that passes through it. The relation between the voltage and the current defines the electrical resistance:

It’s a physical law and, therefore, will always work for any type of electronic circuit.

If the Voltage is directly proportional to I (R = constant), we have the famous OHM’s law.

Most of the resistors used in electronic obey this law, ohmic resistors. Among them are the cluster of carbon resistors, metal film and carbon film.

Practicing - Leds and resistors

To light up a LED we need to limit the current that flows through it, for that we use resistors. If the current that flows through it is higher than recommended, there is a high risk of burning the component.

The video below show’s a led being burned:

Video Soon

The recommended current and voltage between the terminals of the LED depends on the chosen type (color, diameter, shape, etc.). For more details, take a look on the datasheet.

The higher the current, higher will be the light intensity and lower the LED’s life.

Building the circuit:

To light a LED we need:

1 Led
1 Resistor (ohmic)
Power Supply (here we will use 5V and 12V)

So which resistor to use?

Now we are going to see which resistor to use, using the Kirchoff`s Circuit Laws.
They are physical laws, will always be valid for any circuit.

We will use a red LED, when that should work with around 1.7V.
The recommended current for an LED is between 10 mA and 20 mA.
Here we will make the math to use only 10mA.

Using a 5V power supply, we have by Kirchhoff’s Voltage Law

With this, we show that you only can insert the resistor after of before the LED.

By Ohm`s Law:

Therefore:

Now calculating the resistor for 10mA:

Pela Lei de OHM:

Due to the associated error with each resistor and the available values on the market
we will take approximate values.

In this case we do not make approximations of the resistor value
because it’s commercially available.

For a voltage of 12V, R = 1 030 Ω, then we will use 1KΩ.

This article was written by Lucas G. Carli ( lucasgcarli [a] gmail dot com ) - Undergraduate in Electric Engineering

Speeding Up a DC Engine with Magnets

DanielAndrade — Sat, 13 Mar 2010 14:33:06 +0000

Electromagnetism is fun!

Building an Breathalyzer with MQ-3 and Arduino

DanielAndrade — Sun, 07 Mar 2010 06:45:52 +0000

During the First Meeting of Electronic Arts in Florianópolis, we built a Breathalyzer using the Alcohol Gas Sensor MQ-3 and a Arduino Board to use in the last day of the meeting, in which we gave a party. You can see a quick video two posts below. Last days I received many emails asking for the code or how to make one, so I decided to build the sensor again, take pictures/videos and make a tutorial showing how you can make one, so here it is.

Parts Needed:

Arduino Board
10x 5mm LEDs (Green, Yellow and Red)
100KΩ Potentiometer (to calibrate the sensor)
10x ≈ 220Ω Resistor (anything between 220Ω and 470Ω is OK)
BreadBoard
MQ-3 Sensor from Sparkfun

Here are some pictures from the building process:

To make the LEDs work, I have connected them in sequence using the Digital Pins 2 till 11 (ten LEDs total). Remember to use a resistor between 220Ω and 470Ω for each LED, like shown on the picture below:

To connect the sensor, you have to connect one of the H pin to +5V Supply (use an external power supply for that, it may be too much current for the arduino) and the other one to Ground.

Pin B (any of them) you connect to Ground. And the A pin (also any of them) you connect to the 100KΩ potentiometer as shown on the picture below. In the same pin where you are connecting the pin A, you need to connect a wire to the Analog/Digital Converter in Arduino, that is where you are going to read the Alcohol information.

This is a quick and easy DIY project, but if you have any problem building it, please feel free to post questions!

You can DOWNLOAD the .PDE file HERE.

@ Code for interfacing Alcohol Gas Sensor MQ-3 with Arduino
@ Code by Daniel Spillere Andrade and Daniel Amato Zabotti
@ daniel@danielandrade.net / danielzabotti@gmail.com
@ www.DanielAndrade.net

const int analogPin = 0; // the pin that the potentiometer is attached to
const int ledCount = 10; // the number of LEDs in the bar graph

int ledPins[] = {
10,9,8,7,6,5,4,3,2,1 // Here we have the number of LEDs to use in the BarGraph
};

void setup() {

for (int thisLed = 0; thisLed < ledCount; thisLed++) {
pinMode(ledPins[thisLed], OUTPUT);
}}

void loop() {
//This is the code to light up LED's
int sensorReading = analogRead(analogPin);

int ledLevel = map(sensorReading, 500, 1023, 0, ledCount);

for (int thisLed = 0; thisLed < ledCount; thisLed++) {

if (thisLed < ledLevel) {
digitalWrite(ledPins[thisLed], HIGH);
}

else {
digitalWrite(ledPins[thisLed], LOW);
} }}

And now, have a great drinking!!!

Remember, if you gonna drive, don’t drink,
but if you do, call me!

Campus Party Brazil

DanielAndrade — Wed, 27 Jan 2010 18:48:31 +0000

Hi everyone, I am blogging live from the CampusParty Brazil 2k10 in São Paulo - Brazil, it’s something like a Lan Party but full of presentations, concerts and of course downloading… We have here a 10GB BandWidth internet, and there’s a TV screen showing the bandwidth consumption, and we haven’t used more then 3GB at the same time. (I’m trying my best to beat the record). Another thing that I found cool is that someone started a DC++ Servers, and there’s around 400 people connected to it sharing stuff fullspeed, soon my 500Gb Lacie Drive, that I brought with me empty will be full.

In case you are somewhere around the world and would like to download stuff from us, connect to the DC++ Hub cp2010.no-ip.org and download at a great speed.

Today morning there was some people doing Arduino projects, DIY stuff, Open Sorce presentations and much more. You can check LiveStreaming from the Campus Party Here.

Yesterday Kevin Mitnick was here giving a presentation about the art of deception, what a presentation, really good! If you would like to watch it, I am uploading it too, it’s worth it!

Also I am uploading my pictures to my Flickr acc.

Take care all, I will check my downloads now!

I Meeting of Electronic Arts

DanielAndrade — Thu, 21 Jan 2010 13:56:55 +0000

It happened last week, starting on Monday 11th January and finishing on Friday the 15th, the I Meeting of Electronic Arts, where people from many differet places of Brazil came to see what was going on. Our first idea was a meeting (de)constructive, build, hack, modify, learn, teach, freedom of knowledge. Several workshops were presented, Basic Electronics, Processing, PureData, and others (the videos of the presentations will be distributed when people finish editing).

On Tuesday night we made a walking trip crossing the dunes till we find Joaquina’s beach. After swiming in the cold waters, we walked back on a thick rain, amazing, it was long ago since the last time I walked on the rain wanting it!

We learned/teched a lot in this event, one thing that we’ve noticed is that creative minds work much better after midnight. There was no point planning anything for the morning because no one could wake up before 11h.

On Thursday night a party was organized, where we put in for a test some projects developed during the event, for example a Breathalyzer using a Alcohol Gas Sensor MQ-3 sensor, LEDs and an Arduino. By the way, never seen so many arduinos in one place, in different sizes and colors, beautiful!

You can check some pictures from my Flickr:

Here is also a Video from the Breathalyzer (I will make a post on how you can make one after the Campus Party next week)

Some more videos can be found on my Vimeo.

The Longest Way 1.0 by Christoph Rehage

DanielAndrade — Thu, 31 Dec 2009 16:12:42 +0000

Christoph Rehage had an idea of going by foot from Beijin to Germany. He took some shots on his way and afther the trip, made a video. I saw this today and got amazed, so I decided to share with you guys.

also I want to you all to have a Happy New Year and a great 2k10!!!

10 Cool things to do in OSX Terminal

DanielAndrade — Mon, 21 Dec 2009 16:02:20 +0000

The thing that made me buy mac is that it has a OS based on Unix, and programs like Photoshop and Microsoft Office (not a big OpenOffice fan yet). Like a good nerd, I can’t live without my beloved terminal, which makes my life easier. In this post I will show some commands so you can have fun on mac’s terminal. Hope you like it, and if you have any other ideas, please comment on the post!

1. Twitter Update

user

pass

curl -u user:pass -d status=”Tweeting from the shell” http://twitter.com/statuses/update.xml

2. Sing songs

sudo osascript -e ’say “Dum dum dum dum dum dum dum he he he ho ho ho fa lah lah lah lah lah lah fa lah full hoo hoo hoo” using “Cellos”‘

3. Download from a unstable server

–limit-rate 15k

while ! curl -C - -O –limit-rate 15k file-address-goes-here; do sleep 10; done

4. Secure SSH Tunnel

HERE

ssh -D 8080 -f -C -q -N myuser@myserver.com

From: Stammy

5. Real-time view of a running processes

top

6. Resize pictures

.JPG

man sips

sips –resampleWidth 500 *.JPG

7. Build a fast and simple HTTPD server

python -m SimpleHTTPServer 8080

8. Kill a process

top

killall firefox

kill 234

9. Watch Star Wars Episode IV

telnet towel.blinkenlights.nl

10. Show hidden files (those with . in front of the name) in Finder

defaults write com.apple.finder AppleShowAllFiles TRUE

Thanks for readying.

Rare Earth Magnets

DanielAndrade — Thu, 01 Oct 2009 02:56:07 +0000

This is a totally random movie I shot this morning after receiving some Magnets from DealExtreme. Tomorrow I will measure the force of this magnets with a “Gaussimeter”, then let you guys know.

Google: 13 years in 2 min

DanielAndrade — Wed, 19 Aug 2009 12:59:02 +0000

Great movie!

Ultrasonic Range Finder with Arduino

DanielAndrade — Sun, 26 Jul 2009 16:52:12 +0000

I recently got a Maxbotix LV-EZ4 Ultrasonic Range Finder to try understand how to use it with my little Arduino. Having a ultrasonic range finder can be very useful in many different projects, as it can detect objects, I can use it to make alarm systems (cars usually use this kind of sensor), Obstacle-Avoiding Robot and many other things that you may have in mind. It works better outdoors then the IR sensor, but the only thing I could notice is that it doen’t detects very well some thick carpets. Besides that, it’s a great sensor. From the datasheet we can read that it sonar range information from 6-inches out to 254-inches (15.24 cm - 6.452m).

Maxbotix Features:

42kHz Ultrasonic sensor
Operates from 2.5-5.5V
Low 2mA supply current
20Hz reading rate
RS232 Serial Output - 9600bps
Analog Output - 10mV/inch
PWM Output - 147uS/inch
Small, light weight module

Docs:

How the Sonar works:
It basically sends a high frequency wave in one direction, the wave hits a object that reflects the wave. When the wave gets back to the sensor, it calculates the distance depending on the time it takes to go and back. More information can be checked at Wikipedia.

Working with Arduino:

I think the easiest way to work with the sensor is using the Analog Output Mode, where you just need to give the sensor some juice connecting with the 5V and Ground, and the Analog Output on any Analog-Digital Converter pin on the Arduino. Where it gives (Vcc/512) / inch where I am using 5V, so it’s 10mV/inch. But the AD from the Arduino have 1024 steps from 0-5V. So to have the information from the sensor in inches we need to make ADvalue/2 and if you want to have the information in cm, just multiply the previous value for 2.4 (1 inch = 2.4 cm).

Pics:

Video:

So here is the code:
You can download the file HERE.

@ Code for interfacing arduino with a Maxbotix LV-EZ4 Ultrasonic Range Finder
@ Code by Daniel Spillere Andrade
@ www.danielandrade.net -=- daniel@danielandrade.net

int blinkLed=13; // Where the led will blink
int sensorPin=0; // Analog Pin In
int sum=0; // Variable to calculate SUM
int avgrange=50; // Quantity of values to average
int sensorValue; // Value for te average
int i,media,d; // Variables
float cm,inch; // Converted to cm

void setup()
{
Serial.begin(9600); // To check what is being read on the Serial Port
}

void loop() {

d=analogRead(sensorPin); // Read the analog value
digitalWrite(blinkLed,HIGH); // Turn on LED
delay(d); // Delay changes with the analogread
digitalWrite(13,LOW); // Turn off LED
delay(d); // Another delay

cm = (d / 2) * 2.4; // Convert the value to centimeters
inch = d/2; // Value in inches

Serial.println(cm); //Print average of all measured values

// This is the code if you want to make an average of the read values

for(i = 0; i < avgrange ; i++) {
sum+=analogRead(sensorPin);
delay(10);
}

media = sum/avgrange;
Serial.println(media); //Print average of all measured values

sum=0;
media=0;

}

Thanks for reading, and don’t forget to visit www.electronicslab.org