Introduction: Ligten Up Your Room Interior With a Summer Touch

About: I am a University of Edinburgh electronics engineering student.

Summer is approaching! Whether you live close to the sea or high in the mountains it is always nice to remind to yourself how good time is spent on the beach. I decided to do it in a rather interesting way!

This instructable will guide you how to create a nice LED backlighting of any sign that you want. You can hang it on a wall or put it anywhere as it does not require to be close to the power outlets!

The LEDs will automatically turn on when it gets dark and you don't have to worry about turning anything on and off.

The illumination runs on three AA or AAA batteries 1.5V each and is very efficient which means you can almost forget about changing batteries.

# 1 A sound detecting circuit was added in order to turn the illumination down when it is dark but quiet for a set amount of time. This would allow power conservation in the hours when you sleep for example or you are out of the house and there is no need for the illumination to be on. The coolest of all is that you can control this timing and the sensitivity of the circuit very precisely.
See steps 5, 6 and 7!

Step 1: Tools Needed

What you will need to make this instructables is:
  • Breadbord for making the prototype
  • Components
  • Multimeter
  • Shrink tubes
  • Screwdriver
  • Electrical tape
  • Cable nippers and pliers
  • Scissors
  • Empty soldering board
  • Soldering iron
  • Solder wire
  • Hot glue gun
  • Batteries
  • Some thin cables

Step 2: Get Started. Make the Prototype.

The schematic I used for the light detecting circuit is on the second photo.

Components you need for the light detecting circuit are:
  • 2 x 2N3904 NPN transistors
  • 1 x Light Dependant Resistor
  • 1 x 20 kOhms resistor
  • 1 x 2 kOhms potentiometer
  • 1 x 10 kOhms potentiometer
  • LEDs
The number of LEDs you use depends on your project. I used 47 white LEDs. It does not matter how many you put as you connect them in parallel, but not is series. You can mix colours as far as all LEDs have the same operating voltage and need same.

NOTE* Check the pictures' tags. There is the main info.

Step 3: Solder the Board

After you have successfully made and tested the circuit on the breadbord you can start soldering it in. 

As you see I use a simple all purpose board that has holes in it.

Put all the components one by one watching the schematic and solder everything in place. Then cut the board into its final shape and test its operation.

Tune the board with the potentiometers. One will set the light/dark sensitivity and the other will fade in/out the LEDs that you connect to the output.

If you don't like the range that the illumination on/off can be set to, you can change either the 20kR resistor or the 10kR potentiometer that are connected across the base of the transistor (middle leg on 2V3904) and the power supply. Rising the resistance up will lead to a more darker activation of the illumination.

NOTE* Check the pictures' tags. There is the main info.

Step 4: Solder the LEDs Into the Sign's Shape

We are ready with the light detecting circuit board. Now it is time to wire the LEDs.

Initially I taught to make a bridge-like connection between all the LEDs. This would allow me to space them at a larger distance, but would create me lots of work with cutting cables and soldering them.

Instead I decided to bend the LEDs' legs and solder each one to the previous one in a line. Thus all the LEDs are in parallel and if one burns the rest will still work! On top of that you need just around 1.5V to power them.

NOTE* Check the pictures' tags. There is the main info.

Step 5: Add Sound Detecting Circuit

The circuitry has been updated to allow the illumination to turn off when it is dark and quiet at the same time. My idea came from the fact that there is no need for the LEDs to be on at say 4am when everybody is sleeping.

By adding the sound detecting circuit now the darkness is "checked" if and only if there has been some sound above a certain threshold level. If some sound triggered the circuit, then the light detectiong circuit will be powered for 10 minutes to eventually illuminate the LEDs. This time can be adjusted from seconds to hours which depends on you.

What you need for the additional circuit is:
  • ATtiny44A microcontroller (PDF datasheet available here)
  • 1 x 5 kOhms resistor
  • 1 x 10 kOhms resistor
  • 2 x 100 kOhms resistors
  • 1 x 0-5 kOhms potentiometer
  • 2 x 100 nF capacitors
  • 1 x Electret microphone
  • 2 x 2N3904 NPN transistors
As you can see I went through all steps again - drawing the schematic (which I got from a friend that has experience with it), making the breadbord prototype and testing.

But I have to say that I added the second transistor only after I soldered the real board as it did not meet my expectations although tests with the breadbord were OK.

The red LED on the last pictire will be replaced with the first circuit that I made. So if somebody makes sound and the ATtiny44A triggers one of its outputs to logic 1 which are +5V in my case. Then if it is light nothing will happen, but if it is dark the illumination will be turned on. In 10 minutes time if some sound is 'noticed' by the circuit again the 10 minutes countdown will be reset to 10 minutes and on and on untill there is no sound for 10 minutes. 

What you will be able to do with the potentiometer is to tune the sensitivity if the circuit hardwarely. There is no need to reprogramm the chip avery time - just turn and set the potentiometer.

Step 6: Coding

OK, lets code the ATtiny44A

I got this all done by a cool firend that has lots of experience in coding as he is a computer scientist.

You can download both the original and compiled files.
You can read the comments in the original file, but if you have any questions please ask. The 'Beach.hex' file can be flashed immediately to the chip. Note that I have used the 14P3 package and if you want to use other packages you may have to make changes in the code.

To flash the code to the tiny44A my fiend used a AVRISP mkII programmer. You can use anything else of course as far as it is compatible.

Basically the chip gets a voltage in the range 0-5V from one of its legs and compares it to the NOISE_THRESHOLD value which can be set from 0 to 255 for more accuracy. Divide by 255 to obtain the threshold level in volts. It also filters short peaks that may come from circuitry noise. This can be tuned with the NOISE_DIRATION value. You can  also set the on time countdown changing the ON_FOR variable declaration.

It has been a lot of reprogramming to get the threshold and noise duration values correct so you must be patient and consistent!

Step 7: Solder the Final Bits

You will have to solder and cut a new piece of board. Then connect it between the power supply and the light detecting circut. i.e. the light detecting circuit gets power from the output pin that has been programmed on the ATtiny44A chip.

Step 8: Glue the Bits to the Sign

Apply some hot glue to the photoresistor sensor. I have placed it on the upper part of the sign in order to collect the info about the light intensity around. This means that if you swithch the lamp in your room it will reach the LDR from the top and the sign will fade out or turn off completely -   depends on the potentiometer's settings.

Same glue goes to the board and the battery pack.

Step 9:

And so ... we are ready with the light and sound detecting circuits!

Now what you have is a sign that will automatically sense whether you are in the room (because you make noise there) and light up when it gets dark.

My friend made the circuit sensitive enough to pick up noises like speech or a light clap from far.

I should comment on the power effectiveness. During day the whole circuit consumes 3mA and during night if activated - about 10mA.

What a good and interactive piece of the interiour. It is calm and pleasant to look at and best of all - you made it with your hands.

Step 10: More to Want

I will further develop this project adding a sound detecting circuit that will switch the illumination on only if you move around and it is dark at the same time. The idea is that now, when you go to sleep the illuminations stays on till the sun rises up which drains the batteries for no reason.

My idea is if you make some noise a timer to be set on and 10 minutes after you stop making noise the illumination can go off. I will update the instructable as soon as I move on.

Tick this off now!

Thank you for watching. I am waiting for your suggestions and ideas.

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