Thursday, December 20, 2018

Remote Controlled Home Appliance

Parts Required:

1. Arduino, I'm using an Uno for this project.
2. Relay board, I'm using a four channel board to control four devices.
3. Infrared sensor.
4. Standard Television Remote Controller.

Friday, December 7, 2018

Make Speaker/Headphone Bluetooth Capable

Bluetooth capability on your speaker or having a Bluetooth headphone might come in handy in many scenarios and if you are a person like who generally uses Wired headphone or speakers it is normal not to have a Bluetooth capable one. Moreover if you have like an old system that is really good but lacks this modern option you can very easily add that option.

Bluetooth Audio Receiver.

To make this project possible we will be needing a very simple and inexpensive device. This particular device comes in many different quality, price and form factor. Here is one for example.

It pretty much looks like a USB Bluetooth dongle or a Mass storage device but it is nothing of that sort. This is a Bluetooth audio receiver, what it does is connects with your phone/computer via Bluetooth and puts out the audio on that 3.5mm jack you see, That cap is hiding an USB port that is used to power up this device.

The small hole that you see behind the Bluetooth logo can have a microphone or a status LED. Some of these receivers have built in Rechargeable Lithium cell to use without plugging in a stationary power supply.

How to set up?

To use it with a speaker all you need is to put one end of a 3.5mm jack to this Receiver and other end(whether 3.5mm/RCA) to your speaker. Put some power on it and voila, setup is done. Now if you navigate to your Bluetooth settings in your Computer/Phone you should be able to see this particular device.

If you want to use a wired headphone with this device you can do that too, just put the 3.5mm TRRS jack of your headphone in it and power up the receiver if needed and again you are good to go.

In this specific example I'm using a small Power Bank to power it up and it takes a very small amount of power, with a 1000mAh capacity you should be able to run such a device for 1000 hours or so.


1. Some cheaper ones that I tried didn't have the best audio quality, they are often noisy and have an weird ringing sound to it.
2. High quality ones are pretty good, as good as Bluetooth can be which in most cases not as good as wired setup.
3. When using a power supply with it, even though it burns very little power, use a good quality one because low quality ones might introduce even more noise.(Maybe make a small linear regulator?)

Monday, December 3, 2018

Simple Electret Microphone Amplifier

What if you are working on a project that has to pick up audio using an Electret Microphone and couldn't get a powerful signal? Here is a simple solution, a single Transistor amplifier for Electret Microphone.

Components Needed:

2 10KΩ 1/4W Resistor
1 100KΩ 1/4W Resistor
2 0.1µF Capacitor
1 2N3904 Transistor 
1 Electret Microphone
9V Supply



Output can be taken from the output pin and ground pin.

Can be operated on 3V-9V. 


DIY PoE Injector

PoE or Power over Ethernet is simply a way to put Power and Data on the same Twisted Pair Network Cable(E.g. CAT6) so that external power source is not required. This is extremely handy when Cameras and Wireless AP are scattered over a place and difficult to run another power cable to them. To use PoE both device has to be PoE capable but what if you have a PoE supported Camera or AP but not a PoE supported Switch? You can simply use a PoE injector or make one yourself. Now this is not going to be as good as a well made say Maxim chip based PoE injector but it should get the job done.

Component List:

3 4.7kΩ 1/4W Resistors
2 0.1µF Capacitor
1 330µF 100V Electrolytic Capacitor
1 Green LED as indicator
1 58V Zener Diode
2 RJ45 Female Jack
48V DC Power Source


This can be used for DIY projects where 48V PoE is required on 10/100M connection.



This simply puts 48V on the unused pins of Ethernet cable, works on 802.3af 10/100 Mode B. If your source can provide about 400-500mA on 48V you should be able to get about 15W of DC power on the other end which is enough for running a camera or a Wireless AP.


Be very careful with polarity.

Sunday, December 2, 2018

USB Power Injector 5V-12V Variant

USB Power Injector 5V Variant

What can you do if you don't have a Powered USB Hub and you need to power a device that needs more than your standard USB can provide? Here is a quick solution.


1. A pair of USB Male and Female jack, good quality one that can actually carry a good amount of current without dropping significant voltage.
2. 5V Relay.
3. 1N4007 diode.
4. 1kΩ 1/4W Resistor.
5. 100µF 16V Electrolytic Capacitor.
6. An external power supply, 5V 3A or whatever you need.


7. LED and 470Ω Resistor if you need an indicator.


This will not pull much power from your host device so if you need a high powered device say a Hard disk drive to run on a single board computer you can use this diagram. This will omit the necessity of buying a powered USB Hub.


How it works: 

In the diagram USB 1 is the USB male jack that will connect to your host device, say a Single board computer. USB 2 is a Female jack where you can connect your USB hard drive which will be powered by the external power injector from P1 where you can use any 5V supply of your choice, but be very careful about the polarity. 

When USB 1 is unplugged, transistor Q1 stays off, so the relay will stay off as well and there will be no power on the USB2 jack even if the power is available at P1. As soon as the USB1 is plugged in a host transistor Q1 will start conducting as now it has base current provided by the host which will turn on the Relay thus providing power to the USB2 jack from the external power source.

LED will glow when power is available at USB2 jack. 


Be very careful about polarity as reversing it might destroy your USB device. 

C1 is optional, although if this circuit is kind of far from your power supply add another 0.1µF capacitor in parallel with C1 to reduce noise.

You can also add another 470µF capacitor after the Relay to minimize the impact of contact bounce. Just connect it between #2 pin of Relay and Ground, observing proper polarity.

Use a good quality power supply as the external source.