DIY - Table Lamp

Ever wanted to make your own table lamp? If yes then you have come to the right tutorial! This project shows you how to make table lamp using a bunch of LEDs and 555 Timer circuit.

Fig. 1: Prototype of 555 IC based Table Lamp Controller

DIY Table Lamp: Final Set up

Components Required

1. Power supply 12V/1A

2. 5mm white LEDs X 18

3. 555 Timer IC

4. ULN2803 Darlington array IC

5. Resistor 4.7k,10K,680E

6. Potentiometer 100K

7. Capacitors 0.1uF X 2, 10uF electrolytic

8. Diode 1N914

9. Two small PCBs

Designing

Our first problem is that we can’t give 12V directly to an LED which would simply burn it. Well you may say that adding a series resistor would solve that problem but let’s see what happens when we do that.

Fig. 2: Circuit Diagram of LED Driver

Power consumed by LED: 40mW (approx.)

Power consumed by resistor: 120mW

Power consumed by LED + Resistor: 160mW (approx.)

So, there is wastage of 120MW of power while using a series resistor and if this is only for a single LED then imagine how much power would be wasted for 18 such LEDs. Well although it’s not much, we engineers are supposed to design an efficient system right?

P.S. – Adding a voltage regulator would have the same effect (Wastage of power through heat dissipation).

So what else can we do? The answer is: adding LEDs in series! Let’s see what happens when we add 3 LEDs in series and a resistor to it.

Fig. 3: Circuit Diagram of Multiple LEDs Driver

Power consumed by each LED: 41MW (approx.)

Power consumed by resistor: 41MW

Power consumed by 3 LEDs + Resistor: 164MW

So we have successfully reduced the power wastage by almost 80MW. But still as engineers we aren’t satisfied. Are we?

Eliminating the Resistors

The power given to LEDs must be limited which is usually done by resistors or voltage regulator but what else can do that? The answer is Pulse Width Modulation.

PWM is widely used in systems nowadays to control the power going to a particular system. It is just like switching ON-OFF the power to the system but doing it so rapidly that you don’t feel the change. Instead you feel the reduction in power.

So we’ll give our LEDs 12V power supply but using PWM we’ll bring the average power given to it over a cycle to 10V.

Here the Darlington array IC works as a switch and the 555 Timer produces the PWM signal, which is used to rapidly ON-OFF the Darlington array.

Soldering

Part 1: LEDs

Fig. 4: Image showing LEDs and PCB

Take a small PCB and 18 white LEDs

Fig. 5: Image showing LEDs arranged in matrix on PCB

Arrange them in three rows and 6 columns. Once you are satisfied by the positions and spacing between LEDs, mark their positions using a marker.

Fig. 6: Image showing LED terminals popping out on backside of PCB

Now remove all the LEDs and start soldering column by column i.e., three at a time.

Fig. 7: Image showing soldered LED terminals on PCB

Now bend the negative lead of top LED and positive lead of middle LED towards each other. Repeat the same procedure for the middle LED.

Then solder them carefully.

Fig. 8: Image showing polarity of LEDs soldered on PCB

Do the same for other 5 columns. Then start bending the positive leads of all top LEDs towards each other.

Fig. 9: Image showing soldering for positive terminals of LEDs on PCB

Now solder these terminals so that all the columns would be connected to the same +ve end of the power supply.

This is how it looks once everything is done.

Fig. 10: Image showing soldered positive terminals of LEDs on PCB

Top view of the PCB

Fig. 11: Image showing LED matrix on PCB

Remember: While soldering at each step, check if the joints are done correctly and if the LED is working using a multimeter’s continuity feature. This way you can correct the errors in the circuit easily and also replace the LEDs if any of them are damaged.

Making the Circuit

Part 2: Circuit

Take another small PCB. Since soldering ICs directly onto PCB is risky, I’m using an 8 pin base and an 18 pin base for 555 Timer and ULN2803 ICs. Position the bases to see if there is enough space for other components.

Fig. 12: Image showing IC holders placed on PCB

Once you are satisfied, start soldering the bases onto the PCB.

Fig. 13: Image showing soldering done on IC holders on PCB

After the bases, start adding the components one by one.

Fig. 14: Image showing soldered IC holders on PCB

Note: Don’t add the potentiometer right now.

Once the circuit is done, it’s time to combine the circuit with the LED board. For this, cut 6 equal pieces of wires and start soldering one end to the negative leads of each bottom LED.

Fig. 15: Image showing positive and negative wire connections taken out from LED Matrix

Now solder the other end of these 6 wires to the pins 13 to 18 of the base.

Fig. 16: Image showing wire connections between LED matrix and control circuit

Fig. 17: Image showing circuit connections between LED matrix and control circuit

Now solder two wires for the power supply and also a wire connecting the +ve terminal of the top LEDs to the +ve line on the circuit board.

Fig. 18: Image showing power supply connections for PCBs

Now it is time to add the potentiometer. Solder two wires from the board (one from R2 resistor and other from pin 6 of 555 Timer), hook it up and test the light by adding power supply.

Fig. 19: Image showing complete circuit of 555 IC based automatic table lamp

The lights should turn ON and when you adjust the POT value, the LEDs brightness should change now. If not, then you went wrong somewhere.

Fig. 20: Image of LEDs glowing in LED Matrix

Congratulations! You are done with the circuit and soldering part. But still it doesn’t look like a lamp, does it?

The next step is to find a good enclosure for our circuit to fit in nicely. I found a transparent box suitable for it.

Fig. 21: Image showing completed PCB circuits for LED Matrix and 555 IC based circuit

Now I tested by putting inside the box and could still get enough light from the circuit. So I decided to put the LED board too inside only. If you have got an opaque enclosure then you would have to cut a rectangular slot in it to pop out the LED board.

Fig. 22: Image showing complete circuit assembled in a box

We need to make two holes in the box, one for the potentiometer knob and other for the power line.

Fix the pot using the nut given with it.

Fig. 23: Image showing placement of pot on box to control brightness of table lamp

Make another hole, put all the circuit and solder the wires of the potentiometer. Connect the power supply and you are ready to go. The finished setup looks like this: