DIY a Colorful Happy Birthday LED Candle Circuit

The design inspiration of this candle circuit is from our life. In our birthday party, we need to light the candles with a lighter and after making the wish we blow out the candles. This DIY circuit acts like the same way. As we can see from the circuit schematic, the whole circuit is composed of two sub-circuits, one is the audio amplifier circuit which is formed by a 9013 NPN transistor and a 9012 PNP transistor while the other is the switch circuit which is formed by a photodiode and a 9012 PNP transistor.

The working process of this circuit is as below:

In a general night, apply a 4.5V to 5V DC power to the circuit, nothing would happen until an ignited cigarette lighter is approached to the photodiode, the colorful LED light will start flickering. When you blow toward the mini microphone, the LED will be turned off.

Insert the resistors into their corresponding position on the PCB. Every position has its belonging resistance value printed within the white rectangle. How to get the resistance value of the resistors? There are two basic methods to approach this goal. One is reading from the color bands printed on their bodies, for more details please refer to this blog. The other is much straightforward that is to measure it out by a multimeter. Just need to follow from image 1 to image 4 to complete this step. You should beware of the small spikes created by cutting off the excess legs of the resistors as shown in image 3 and image 4.

Insert the 102 and 103 and 104 ceramic capacitors into the PCB and then solder. Each corresponding position of the ceramic capacitor has its belonging value printed within the white rectangle. Please make sure don’t get the ceramic capacitors to insert into the wrong position.

Just like as shown in image 7, each transistor has its model number printed on the flat surface side. S9012 is a PNP transistor while S9013 is an NPN transistor. Please insert them into the white semicircles on the PCB. The transistors should be inserted into the semicircles with as the same model number printed on the PCB as the transistors themselves.

What is Photodiode? A photodiode is a semiconductor device that converts light into current. The current is generated when photons are absorbed in the photodiode. A small amount of current is also produced when no light is present. Photodiodes may contain optical filters, built-in lenses, and may have large or small surface areas. Photodiodes usually have a slower response time as their surface area increases.

The photodiode should be inserted into the D2 while the colorful LED should be inserted into the D1. The long legs of both of the photodiode and colorful LED should be inserted into the hole near the ‘+’ symbol.

Follow image 12 and image 13 to insert the potentiometer and mini microphone into the PCB. Please make sure that the top view of the mini microphone should be matched against the white circle printed on the PCB.

Just as like as marked in image 14, the hollowed semicircle on the surface of CD4013 should be placed in the same direction of the small semicircle embed in the width of the white rectangle. When you first receive just about any DIP IC, the legs will not be parallel to the main chip body. The legs will bend out slightly. In my experience, it is best to adjust them before trying to insert into the IC socket. It is very important that this step be done with care, to avoid damaging the chips. Go slow, use light pressure, and take your time. Grasp the IC with 2 hands and make the pins adhere to the desktop. You want to bend the pins at the same time so they bend right where the pins change from wide to thin, use a slow, steady, and even pressure to bend them all at once until they go straight down from the chip.

Apply from 4.5V DC to 5.0V DC to the power port, J1. Ignite the lighter near the photodiode, you will see the colorful LED start working. If you want the LED to be turned off, just need to blow towards the mini microphone. This is a circuit to simulate the process of igniting a candle and blowing out the candle, it can be used as a demo circuit to expand to more LED lights in your special customized party decoration. Sample material is available at Monday Kids DIY Store