Tuesday, February 14, 2017

Musical Doorbell

This post is about making a simple musical doorbell circuit that can be used in your house and might take only couple minutes to build it.

Goal here is pretty simple, it will be a musical doorbell that has a very small power consumption and can play the music for couple moments even after releasing the momentary doorbell switch. For the music we will be using a melody generator integrated circuit to make our work easy and to turn on and keep it on we will be relying on Capacitor and transistors, so let's take a look at the component list.

Component List.

1. Integrated Circuit UM66.
2. Transistor 2N3904, 2N3906, SS9013, one piece each.
3. Capacitor 100uF.
4. Resistor two 1Kohm, and one 10kohm and one 100kohm.
5. Battery holder two AA size.
6. Speaker 4/8ohm.
7. Momentary press button.

Let's talk about music!

Part number of the UM66 will give us an idea of what music it is going to generate. To find the right music for doorbell buy the one with the right part number.

The diagram!

Now that we know which Integrated circuit to order let's build the circuit.

How does it work? 

Power source for this circuit is two AA size cell, preferably Alkaline. They will provide roughly 3V.

When SW1 or the momentary press button is pressed the 100uF capacitor will be charged and at the same time the 2N3904 transistor will start conducting as it is getting current to it's Base.

As the 2N3904 can now be treated as a close switch we can assume the Base of 2N3906 to be at the ground which will cause the 2N3906 to start conducting.

Now we can see the current can enter into the integrated circuit causing it to turn on. This circuit will output a melody signal which will be amplified using SS9013 transistor which is feeding a loud speaker.

If the momentary switch is released, the 100uF capacitor will discharge through the 10kohm resistor and the 2N3904 transistor. So it will keep the circuit alive for couple moments after releasing the switch. Once it is fully discharged both the transistors will be open again and the integrated circuit will not get any power to stay On.


1. You can use ZL66 instead of UM66 too.
2. Two AA Alkaline cells will be fine for this doorbell.
3. A normal 1-3W speaker will be fine.
4. Increasing the value of the capacitor will cause the circuit to stay alive longer after the press button is released.
5. Both the 2N3904 and 2N3906 can be replaced by similar NPN and PNP transistor respectively.


1. UM66 Datasheet.
2. SS9013 Datasheet.
3. Read my other posts.

Tuesday, December 13, 2016

Show Temperature on 16x2 LCD with LM35 and Arduino

Good evening everyone so in my Arduino series last two posts were about temperature reading, displaying it on Serial monitor and using a 16x2 LCD display. Now allow me to merge them together to show the temperature reading in that display.

Parts Needed:

1. Any Arduino board ( And yes I'm using the UNO);
2. USB Type A to Type B cable to connect to computer and upload the code.
3. 16x2 LCD Display.
4. Male to Male Jumper Wire.
5. Practice Board.
6. 220ohm Resistor.
7. 10kohm Variable Resistor.
8. LM35.
9. Arduino IDE.


Let's start with the display.

Pin 1 - Ground.
Pin 2 - +5V.

Pin 3 - Connect to the Wiper Terminal of the variable resistor. Variable resistor needs both Ground and +5V on it's other two terminal. This resistor is used as contrast control.

Pin 4 - Register select, connect this to Arduino pin 12.

Pin 5 - Read or Write pin. Connect it to the Ground to enable Write mode.

Pin 6 - LCD Enable Pin, connect it to the Arduino pin 11.

Pin 11 - D4 to Arduino pin 5.

Pin 12 - D5 to Arduino pin 4.

Pin 13 - D6 to Arduino pin 3.

Pin 14 - D8 to Arduino pin 2.

Pin 15 - LED+ to 5V/3.3V with a series resistor maybe a 220ohm one. I'm using a 1K one though.
Pin 16 - LED- to Ground. 

Now let's hook up the Temperature sensor.

Pin 1 - +5V
Pin 3 - GND

Pin 2 - Arduino Analog input pin 5.

That's pretty much the connection that we need.

The Code:

Here is the code with necessary explanations.

// Let's start with including the LCD Library.

#include  <LiquidCrystal.h>

// Define the Input pin for LM35, in this case it is A5.
int  tempPin  =  5     ;

// Declare variable
int  value;

// Initialize the library with the numbers of the interface pins.
LiquidCrystal  lcd    (12, 11, 5, 4, 3, 2);

void  setup()

  // Sets the data rate in bits per second (baud) for serial data transmission.

  // Set up the LCD's number of columns and rows.
  lcd.begin(16, 2);

  // Print a message to the LCD.
  lcd.print("Temperature: ");


void  loop()

{ // taking in the value from input pin.
  value = analogRead(tempPin);

  // convert the voltage information, as LM35 is already calibrated in celcius to get the celcius output not much code is needed.
  float mv = ( value / 1023.0) * 5000;
  float cel = mv / 10;

  // convert the celcius value to farenhite, uncomment this and print it to get the fahrenheit result.
  //float farh = (cel * 9) / 5 + 32;

  // Serial Print will print value to serial monitor.
  Serial.print("Temperature = ");

  // Let's give it a vertical shift so it will be on the bottom line.
  lcd.setCursor(0, 1);

  // Print a message on the bottom line.
  lcd.print(" *C") ;

  //Start again after 300ms.


So how does it work?

Well I have separately written how the display and the temperature monitoring works so I will just put links to those post at the bottom of this post where you can find details on them.

Let's look at the completed project.

Here you can see the display, Arduino and the LM35. The reason there is no variable resistor is because I don't need to control the contrast in this one. So I just left it out.


Temperature sensor can be really helpful and putting it on a display can be even more helpful. It not only can be used as a visual modification for your project but can be used in many different projects where it is necessary to show the temperature. You can also control other devices using temperature as the trigger point. One thing you can do is to make something like the following image and cover the wires with heat shrink material and can be used as a temperature probe to lower it in a liquid or reach in a place where it wouldn't be practical to put the practice board in.

In Here I'm Just using three Male to Female jumper wire, the one that is used with Raspberry Pi.

So that's pretty much it, hope this has been helpful.


1. Temperature monitor using LM35.
2. Using 16x2 display with Arduino.
3. Read my other posts here.

Monday, December 12, 2016

Temperature Monitor Using Arduino and LM35

Good evening. This is the continuation of the Arduino series and this particular one is about how to make a simple temperature monitor using the LM35 precision temperature sensor.

This will a very small project as the part it needs is the LM35. Reason behind that is this small chip is already calibrated in centigrade so it is just as simple as reading it's output value, do a small conversion and show it on display or use it in somewhere. LM35 is a linear temperature sensor and it's output voltage is proportional to the temperature. It's output is 10mV/Degree Centigrade. So if you rise temperature by 1 Degree Centigrade, output will increase by 10mV. So all you have to do is read that through Analog input pin of your Arduino and done. There are couple different positive things about using this. It has wide voltage range, it is a very small device so it is suitable for pretty much any application where temperature reading is needed.

So let's go over the parts list:

1. Arduino, again for basic projects like this I use UNO.
2. LM35.
3. USB A to B cable and Jumper Wires.
4. Arduino IDE on computer
5. Practice Board.

Procedure and Connections:

As there will be no other parts other than the LM35, the connection is pretty simple. LM35 has three pins. Pin1 takes in positive voltage which can be anything from 4V to 30V and Pin3 is the ground pin. I have just powered it directly from the Arduino 5V and GND pin.

Pin2 is the output pin of LM35 which needs to be connected to any of the analog input pins of the Arduino. You might have to change the code if you use anything other than 5 because that's what I'm using.

After connecting upload the code provided, code has all the necessary explanation and how you can modify it. Then open up the serial monitor to see the temperature reading.

The Code:

// declare variables.

int value;
int tempPin = 5;

void setup()
void loop()
  // taking in the value from input pin.
  value = analogRead(tempPin);

  // convert the voltage information, as LM35 is already calibrated in celcius to get the celcius output not much code is needed.
  float mv = ( value / 1023.0) * 5000;
  float cel = mv / 10;

  // convert the celcius value to farenhite
  float farh = (cel * 9) / 5 + 32;

  Serial.print("Temperature = ");

  /* uncomment this and comment the previous 5 lines to get temperature in farenhite
    Serial.print("Temperature = ");


Here is the project:

How does it work? 

I have talked about LM35 earlier on this post, so you get the idea of what happens with different temperature, it gives different output voltage which is analog. Hence we put that in the analog input of Arduino. Now we have to convert it to digital in a way that it represents the proper temperature value.


 You can check for the accuracy using a source with known temperature.


This one might be a very simple project but you can use it in many different things like battery over temperature protection or any kind of over temperature protection. It can also be used to control devices based on temperature. 

Hope you have enjoyed it.


Sunday, October 30, 2016

Easy Chat Program using Arduino.

Good evening everyone. So in this day of age anyone who is interested in electronics or keep an eyes on technological news Arduino should be a very common word for them and rightly so because it has made designing and implementing circuits so simple that even amateur people can actually make awesome things this days. Arduino has pretty much gave everyone the power to make something which was previously kinda on the hands of people who knows about how things work. Anyway you can already guess this post will be something using Arduino and it is a simple chat program.

So what this will allow us to do is just send and receive simple text from a computer. Yes I understand there are much better options out there but this one will help you to get familiarized with Arduino and show you how easy it is to get things done.

Parts needed: 

1. A pair of Arduino. I'm using the ever popular and cheap Arduino UNO.
2. A pair of USB Type A to Type B cables to connect Arduino with computers.
3. Two Male to Male jumper wire or similar cable to connect the Arduinos.
4. Arduino IDE on computers.


1. In this particular example I'm using the Arduino pins 7 and 8 but you can use any pin you want all you have to do is to change the code accordingly. I have used 7 and 8 because they are easy to find. Just connect pin 7 of one Arduino to pin 8 of the other. So there will be two wires connecting both the Arduinos.

2. Make sure the IDE is installed on your computer, it can be downloaded from their website for free.

3. Connect the Arduino via USB port and upload the Code found in the Direct Chat Code file, link will be on the bottom of this post. You need to put the exact same code in both of them. Make sure to select the correct COM port before uploading.

4. Now open up serial monitor and you can start chatting.

The Code:

/* Simple Chat Program

 Receives from the hardware serial, sends to hardware & software serial.
 Receives from software serial, sends to hardware serial.

 The circuit setup:
 * RX is digital pin 10 (connect to TX of other device)
 * TX is digital pin 11 (connect to RX of other device)

 Created and modified by Redwan Hasan based of software serial example.
#include <SoftwareSerial.h>

SoftwareSerial chat(10, 11); // Define RX, TX

int text;

void setup() 
  // open hardware serial, TX = 1, RX = 0
  Serial.println("Welcome to the chat program...");
  // set the data rate for the SoftwareSerial port

  // delay 1s to stabilize serial ports

  chat.println("Your Friend is online");

void loop()
  if (chat.available())
  if (Serial.available())
    while (Serial.available())
      text = Serial.read();

Here is the project.

Working Circuit for this project

So how does it work?

The basic idea is very simple here, the pin 7 is the RX pin and 8 is the TX pin. The way we have connected them is from TX to RX and RX to TX. What's gonna happen is this, what one is transmitting other will simply receive it and put it on display and as the path is bi-directional anyone can send and receive.


Here it is, a bi-directional conversation can be done here. I have used one a single computer to connect both the Arduinos but you can use two computers and essentially chat with someone else.

Hope it has helped.


1. Arduino webpage.
2. Read my other posts.

Tuesday, September 20, 2016

Fleming's Both Hands Rule!

Good afternoon everyone, so I think today is a good day to write about something kind of confusing which is Fleming's Left hand rule and his right hand rule. These rules are just mnemonic or you can call them memory technique to remember the directions of current, magnetic field and motion in both motor and generator.

So first things first remember this;

1. Fleming's Left-hand rule is used for electric motors.
2. Fleming's right-hand rule is used for electric generators.

Now let's talk about how to apply these rules, starting with left-hand or the motor hand.

As we are talking about motor the current and the magnetic field will be given but the force direction will be unknown. If a current carrying wire is subjected to a magnetic field in a perpendicular fashion then the wire will feel a force which is perpendicular to both the direction of current and magnetic field. So we are talking about 3 axis here, if you set say the field and current to x and y axis respectively then the motion will be in z axis. Things are a bit complicated without any visual representation.

Here is a left hand diagram where

Thumb or F is the force vector or the thrust on the conductor or motion of it. 
Fore finger or B represents the direction of magnetic field or flux density.
Second finger or I represents the direction of current.

Let's move on to the right hand rule now.

For generators however the motion and the field is given we need to know the direction of current. So thing is if we subject a moving conductor in a magnetic field we will get current which is both perpendicular to the two applied causes. Again let's look at a visual representation.

In here

The thumb is the motion of the conductors.
Fore finger is the magnetic field.
Second finger is the direction of current.

So that's a brief description of Fleming's left and right hand rules.

For more info visit the wiki links.

Left hand.
Right hand.

You can also read my other posts here.

Index to my blog.

Monday, September 5, 2016

Raspberry Pi Starter Kit

Good evening everyone. Hope you guys are doing great. So currently single board computers are very popular and getting more more and more popular day by day. Truth to be told there are huge amount of legitimate reasons behind their popularity. If you are however new to all these then this post might help you out. In this specific post I will be focusing on Raspberry Pi and I will go into the reason why in a few moments.

Like I was saying if you are new to this whole single board computer thing I would say start with Raspberry Pi as it has been here for quite a long time so you will get more support. Now let's take a look at what you are going to need to properly work with Raspberry Pi in many different scenarios. So couple things are common for all scenarios, let's start with them.

1. You will obviously need a Raspberry Pi, as for September 2016  I would suggest getting either a Pi 2 or Pi 3.

Raspberry Pi 3

Raspberry Pi 2
Let me give you a bit more info on this single board computers. Both of them are ARM based and have a lot of similarities but the newer one has couple more tricks up its sleeve.

System on Chip:

RPi2: BCM2836 Quad Core ARM Cortex-A7 900MHz with VideoCore IV 250MHz
RPi3: BCM2837 Quad Core ARM Cortex-A53 1200MHz with VideoCore IV 300MHz

Audio and Video Output:

HDMI supports 1080p video with audio.
3.5mm TRRS jack for Stereo Audio and Composite Video.


RPi2:  10/100Mbps Ethernet Port via an USB to Ethernet Adapter on-board.
           4 USB 2.0 Port.
           1 HDMI, 1 3.5mm TRRS Jack.
           40GPIO Pins,
           Camera Interface(CSI)
           Display Interface(DSI)
           MicroSD Card Slot for Loading Operating system.
RPi3:  10/100Mbps Ethernet Port via an USB to Ethernet Adapter on-board
           Bluetooth 4.1Classic, Bluetooth LE, Wi-Fi 2.4GHz 802.11n Standard.
           4 USB 2.0 Port.
           1 HDMI, 1 3.5mm TRRS Jack.
           40GPIO Pins,
           Camera Interface(CSI)
           Display Interface(DSI)
           MicroSD Card Slot for Loading Operating system.

5V 2A(Recommended) via Micro USB.

So the major difference here is the Improvement on the CPU side as frequency is bumped from 900MHz to 1200MHz and also the GPU sees a little improvement. The big advantage here is the fact that Raspberry Pi 3 comes with Wi-Fi and Bluetooth. Next thing we need is microSD card to load operating system.

2. MicroSD cards.

As they are inexpensive I would suggest you to buy about 4 of them, 16GB of capacity and Class 10 in speed specification. That way you can keep one or two stable operating system ready in hand to use and maybe one or two more for experimenting.

3. A good power adapter.

To power up the device properly a good quality power supply is needed with a good micro USB cable. Personally I use phone chargers and they work just fine. I would suggest getting at-least 2A one but if you plan on using portable Hard drive or something I would recommend getting a 3A one. (Although keep in mind that the combined current output of all four ports are 1.2A)

4. Ethernet cable or Wi-Fi dongle:

Depending on which method you use, you might need an Ethernet cable, a CAT5e would be enough or you can opt for a USB Wi-Fi dongle for RPi2 but for the RPi3 it has built in Wi-Fi. If you are plan on using network attached storage however I would recommend using the Ethernet port as it will provide more consistent speed and better latency.

5. HDMI Cable and 3.5mm splitter:

For connecting with TV or monitor I would recommend using HDMI as it is better and easier to configure as oppose to the composite output, however if you still want to use that you can use another 4 pole to two 3 pole converter. The one that will work with Android or apple devices will also work here to. What it will do is just take in the A/V signal and give out separate stereo audio and composite video. In case of using the same jack with laptop's combo port or phone you will get stereo audio out and microphone in. Don't fall for the HDMI cable money trap though, 5$ one worked exactly like a 50$ one.

6. USB flash drive.

If you are plan on using NAS or Media Center or maybe RetroPi gaming setup, you might need this. Don't bother with USB3.0 however because ports on Raspberry Pi2/3 are of USB2.0 standard.

7. An analog game controller.

If you plan on using RetroPi this is a must for you. You can get either the wired one or wireless one.

8. (under construction)

Tuesday, August 30, 2016

Setting up DHCP address reservation

Good afternoon everyone, in this brief post I will talk about how you can enable DHCP address reservation on your router. For demonstration purpose I'm using a TP-Link router which is very common but any other brand of router should have the similar option too.

Before getting into how to do it let's discuss DHCP. It stands for Dynamic Host Configuration Protocol and as it's name suggests it is an network protocol used on Internet network protocol. This protocol is controlled by a DHCP server to dynamically distributes network parameters such as IP addresses. So it drastically reduce the workload for the network engineer who is in charge with deploying a network. If DHCP wasn't available network engineer or the person who is setting up the network has to manually assign IP addresses to all the devices but with DHCP the server itself assigns IP addresses to devices automatically. Connect a new device and it will get a new IP automatically, you don't have to do anything. If you think about depleting IP addresses then lease time will help you with that. Unused IP addresses will be re-cycled via this. DHCP server leases IP for certain set period of time, if after that time the device no longer needs the IP it will be assigned to some other device. So it's all well and good right then where is the point of reserving certain IP?

Here is the thing, if you are running a network attached storage or IP TV or media center then DHCP might not be ideal as it will change the IP address over time. Say if you configure your phone to get certain data from certain IP, if that IP changes it will no longer get that data, you will have to enter the new IP. Now if you completely turn off DHCP then again you have to manually set all the IP addresses for different devices. Hence DHCP address reservation. In this method what is done is simply reserve certain IP address to certain MAC address or device address so that that IP won't be given to anyone. This ensures that certain devices will always get certain IP addresses. For example I always reserve IP address for my Raspberry Pi so that I can easily SSH into them. Let's look at the procedure then.


1. Get into the router via the web based interface, for different router it might be different for example
Tp-link can be accessed with or tplinklogin.net
SMC can be accessed with

After that login with the username and password, it should be written under the router or on the box if you haven't changed it yet.

2. After getting into the router you will be greeted with this page where you should find something like DHCP. We need to get into that too

3. Now getting into DHCP we will find the options for turning it on or off. Default it should be enabled and we want to keep it that way.

4. Next we need to go to the DHCP Client list to get the MAC address for our client. If you can't determine the device from the client name, for example it is very tough to determine android devices so in that case you might want to gather the IP address or MAC address from the device itself. Keep that MAC address in mind to assign the IP address that you want to assign. Remember the lease time I was talking about? Look carefully and you will see some devices have their IP address with lease time, after the expiration either those IP addresses will be renewed or given to some other device if needed. Those with the Permanent lease time are reserved.

5. Now let's move on to the final part the Address reservation, in here you will see any existing one that is already configured or you can add/modify/delete any entry.

6. As I already have couple devices configured to have same IP address all the time those devices are already listed here. If you are doing it for the first time you will see an empty table. To add a new entry you simply click Add new and put in the MAC address and IP address and done. You might want to restart the router afterwards.

So that's how easy it is got enable DHCP address reservation and saves a lot of time finding IP addresses of devices. Now for an example I will always reach my Raspberry Pi 2 at

Hope it has helped.

Read my other posts here.