Friday, October 17, 2014

Temperature Sensor For Development Board

Welcome back and good day everyone.

This will be a small post about a temperature sensor that can be used with development boards like Arduino, Raspberry Pi or similar products. This circuit is a very simple and easy to make circuit. This circuit is based on a precision integrated circuit that has an output voltage linearly proportional to temperature. So higher the voltage is higher the temperature is. We can simply read the output voltage and convert it to centigrade temperature scale.


+2 Degree To +150 Degree Centigrade

-55 Degree To +150 Degree Centigrade

How It Works?

LM35 looks like a small TO-92 package transistor but it actually is an integrated circuit. This integrated circuit is from Texas Instrument. This IC can be operated from 4V to 30V, that means you can't run it on 3.3V but 5V will be fine for it.

If you check the datasheet of the IC you will see that it's output is Linear + 10mV/Degree Centigrade that means 10mV represents 1 degree Centigrade. So 0.25V will represent 25 Degree Centigrade. Although this IC can read from -55Degree to +150 degree, you will need slightly different diagram for that and also you will need dual polarity power supply for that. For the value of resistance use the theorem to calculate the value.

From the circuit diagram it can be seen that it is powered from a 5V source, a capacitor is used to slightly stabilize the output. You can use a lower valued one or higher valued one if you want(even a 100uF electrolytic will be fine). This circuit can easily be built on a small PCB. 

How to Interpret

While converting A to D ( Analog to Digital ) all you need to do is to use the fact that 10mV stands for 1 degree centigrade, Measuring the voltage you will get the actual temperature. 

More Information

1. LM35 Datasheet.
2. Dual Polarity Power Supply.
3. My other posts

Happy Experimenting.

Monday, October 13, 2014

Single/Multi Channel Relay Board

Good Morning. You may have heard or even used something like a Relay Board and often these boards can cost good amount of money but they are very simple to make so here is a few diagrams for making one. Board diagrams shown here can be used with Arduino or any similar development board.
Typical Relay Board

You can make many different types of Relay boards for ease of explanation I will be separating them based on how many channels they have and the power source they use.

For channels, it is quite simple, each relay will act as a switch so more switch you need more relays to be added and we can simply call each switch a Channel.

These relays can be powered both by the Development board itself or from an external power. If you don't have many external components on your development board and just want to run a single relay, you are fine with using power from the board but if you plan on using good amount of Relays or if they run on 12V you are better off powering the relays from an external 12V source.


These boards are essential if you want to control any external device running on different voltage or maybe controlling something that is on the main line. Say for example you want to make a Remote controlled ceiling light, for that you can easily use a single channel relay board with your development board of choice.

1. Circuit/Vero Board.
2. Diode,
3. Transistor,
4. Relay,
5. Resistor,
6. Connector


7. LED as status indicator. 



Single Channel 5V Relay Board

Single Channel 12V Relay Board

Dual Channel Relay Board
How It works:

Electromagnetic relays are switches that opens or closes with the help of an electromagnet, relays that are used here(the garden variety 5 pin one) usually connects the Common(C) pin to Normally Connected(NC) pin. When the electromagnet is energized with proper voltage the Common(C) pin then disconnects from Normally Connected(NC) and gets connected with Normally Open(NO) pin.
I have written about Relays in much more details so not gonna repeat much, link of that post should be in the Information section below.

Transistors are there to drive those relays as often Signal pins of development boards do not provide enough power.

A LED can be used as an Indicator.


1. While using an external 12V power source for relay, make sure it is regulated unless Relays might make noise/hum.
2. If your Signal pin needs to be pulled down, add that pull down resistor.
3. You can simply add more channels to any of the diagrams and have more relay channels.
4. To use an external source make sure to tie down both ground pins together.

1. Learn about relay here.

2. Read my other posts here.