Project 55: Electronic Candle
This project involves two extra components which are not in use in the other projects
These components are the Quad Op Amp, and the Cds Cell
Below I’ve provided the role of each component, and how they function.
Quad Op Amp- An integrated circuit which is an electronic circuit formed on a small piece of semiconducting material which performs the same function as a larger circuit made from discrete components.
Cds Cell- A Cadmium Sulfide Cell which can be used as an automatic control. It is a semiconductor which means it conducts electricity, but also partially resists electricity. The cells resistance changes with the amount of light shined on it.
Project 55: Electronic Candle
Now that I have information on the other components used in this project, I can move on to connecting the circuit.
The components are connected as described below.
1-26-87-97, 3-29-14-45, 13-105, 17-106, 18-36, 19-40-107, 69-27-88, 28-90-98, 70-89-42-43.
The connection from 1 to 26 to 87 to 97 connects the left terminal of LED 1, to the top left of the quad op amp, to the left side of a 10k resistor, to the left side of a 100k resistor with two medium sized red wires and a small white wire.
The connection from 3 to 29 to 14 to 45 connects the right terminal of LED 1, to the GND of the quad op amp, to the right terminal of the Cds cell, to the negative terminal of a battery with one medium sized red wire and two small white wires.
The connection between 13 and 105 connects the left terminal of the Cds cell, to the left terminal of the control with a medium sized red wire.
The connection between 17 and 106 connects the base of the Q1 PNP transistor, to the middle terminal of the control with a long yellow wire.
The connection between 18 and 36 connects the collector of the Q1 PNP transistor, to the VCC terminal of the quad op amp with a medium sized blue wire.
The connection from 19 to 40 t0 107 connects the emitter of the Q1 PNP transistor, to the positive terminal of a battery, to the right terminal of the control with one medium sized blue wire, and a medium sized red wire.
The connection from 69 to 27 t0 88 connects the positive terminal of a 10 micro farad capacitor, to the quad op amp, to the right terminal of a 10k resistor with two medium sized red wires.
The connection from 28 to 90 t0 98 connects the quad op amp, to the right terminal of a 10k resistor, to the right terminal of a 100k resistor with one medium sized red wire, and one small white wire.
And finally the connection from 70 to 89 to 42 to 43 connects the the right terminal of a 10 micro farad capacitor, to the left terminal of a 10k resistor, to the negative terminal of a battery, to a positive terminal of a battery with one medium sized red wire and two small white wires.
Once all the connections have been made LED 1 illuminates if the control is set to zero. By turning the control clockwise toward ten, the LED will turn off. The LED flashes in rapid succession simulating the light of a candle.
To see the LED electronic candle please click here
The electronic candle uses a Cds cell which reacts to the amount of light it receives. By covering the Cds cell the light dims, or goes out completely depending on the coverage. As the amount of light gathered by the Cds cell changes, the OP Amp’s power voltage changes in order to control the oscillation. The two changes are related, and as light increases, the output voltage of the transistor increases (or is amplified), as the light decreases the output voltage of the transistor decreases. This creates the flickering of the LED, and the changes in brightness due to the coverage of the Cds cell.
You can see what happens when covering the Cds cell here
The OP amp is a long period oscillator which means the output it creates lights LED 1. The Q1 transistor amplifies the input from the Cadmium Sulfide cell to the OP Amp. The output of this activates the OP Amp.
This project varied from the entertainment circuits as it dealt with light rather than sound. The flickering candle also involves the use of the Cds Cell, and the OP Amp in order to function. Completing the project made me more interested in how the OP Amp and Cds function, and how they can be applied to other electronic projects.
Sources: Maxitronix Electronic Lab Owners Manual