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

Relay Board For Development Boards

Good evening everyone, hope everyone is okay. You might have heard the term development board or you might even used one. If you want to control a high voltage electrical device using these type of boards you will need something called the relay board, it is actually a simple relay being powered from the main 5V(typically) source and only powered when the signal is there. These board's output pins provide very low amount of current, which is not adequate to run a relay or relays, so a transistor is being used as a switch in here.

What is needed?

1. PCB or any type of board,

2. Diodes,
3. Transistors,
4. Relays,
5. Resistors,
6. Light emitting diodes(optional),
7. Connectors.


Single Channel Relay Board
Diagram is pretty straightforward, as we all know relays are just magnetic switches, so powering up the coil will activate the switch. Usually relay's common pin touches the Normally connected pin and powering it up, common pin touches the normally open pin.

As I have stated earlier that power from the board might not be enough from driving a relay so we will just provide the signal to the base of a transistor and thus use the transistor as a switch.

The diode with the relay is needed to protect other devices from being damaged. 

LED will give a visual information that power is available across the relay, which means it is in the on position. 

The 5V and +Voltage switch can be used to use two different sources, just remember to tie up both the Grounds together. 

You can use any suitable NPN transistor for this but for a single relay a D400 or even a 2N2222 would be enough.

Two Channel Relay Board
This diagram is the same as the earlier one just the difference is it has two different inputs and two relays. You can just add another relay to control one more element. 

You can just buy this from stores or suppliers but why buying when you can make one for yourself? Happy experimenting!

1. Learn about relay here.

2. Read my other posts here.