S2 Create and interpret circuit diagrams

Posted: October 10, 2010 in Systems and Control

Initial knowledge – 1

Current working knowledge – 2

I have a slender knowledge of circuit diagrams from my days at secondary school, we did have an electronics department and it was one of the compulsory subjects of design technology before we took our options at GCSE.  I’d love to say it came second nature and I went on to have a fantastic knowledge and working understanding of circuits but unfortunately year 9 was where my fleeting brush with circuits and circuit diagrams ended until now.

As I remember a circuit diagram or I think it was also referred to as an electronic diagram was a simple graphic or (schematic) representation of an electrical circuit.  The circuit diagram features simplistic standardized drawings representing the various components featured in the circuit :

These are the standard symbols you would find in a circuit diagram, I am familiar with a few of them for instance the battery, resistors, fuse, leds, and the various switches. I am also aware that a circuit diagram will actually show the wire connections being used and with this principal I used the programme circuit wizard to design the circuit for my ambiance light.

circuit wiz word

circuit diagram

These are relatively simple circuits which are both the same but just layed out differently and I could interpret them easily enough to design my working circuit.  The circuits feature my PIC chip, a 9v battery, 2 switches and 3 leds that are protected by resistors.  However I already knew about these components and so I need to do a bit of research on the others to see what their functions are and gain a general knowledge in case I wish to use any of them in future designs. Or need to interpret the circuit diagrams of other people using them.

I need to research some of the other components and find out what their function is:

Potentiometer: A potentiometer is a manually adjustable resistor. The way this device works is relatively simple. One terminal of the potentiometer is connected to a power source. Another is hooked up to ground, while the third terminal runs across a strip of resistive material. This resistive strip generally has a low resistance at one end, its resistance gradually increases to a maximum resistance at the other end. The third terminal serves as the connection between the power source and ground, and is usually interfaced to the user by means of a knob or lever. The user can adjust the position of the third terminal along the resistive strip in order to manually increase or decrease resistance. By controlling resistance, a potentiometer can determine how much current flows through a circuit. When used to regulate current, the potentiometer is limited by the maximum resistivity of the strip.  Think volume control on a hi-fi.

Thermistor :  A thermistor is a resistor whose resistance varies through significant temperature change.  Think Jacques egg timer.

Light dependent resistor: A resistor whose resistance decreases with increasing light intensity.  Think traffic lights that re-charge over night.

Polarized capacitor: A polarized capacitor is one which has a polarity,  positive on one terminal,  negative on the other.  This makes it superficially look like a battery. In use, the capacitor has its positive voltage always higher than that on the negative terminal, it matters that this is the case and this gives rise to the term polarized. This sort of capacitor is commonly found in power supply filters.  Think storing charge for timed circuits, Toms cat feeder.  A non-polarized can be wired either way.

Diode: Only allows electrical current to run one way.

Transistor: Is used to amplify and switch electronic signals.  Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal.  Think smaller radios and computers.

Amplifier: An amplifier is an electronic device that increases voltage, current, power or signal.  Amplifiers are used in wireless communications and broadcasting and in all types of audio equipment.

Fuse: A fuse is a safety device that lies in series in a circuit between an electrical source and its associated load(s). When the current, or flow of electricity, exceeds its designed threshold,  the fuse is calibrated to permanently open the series circuit, thereby disconnecting the load(s) from the power source.   Unlike circuit breakers, which can be reset to allow current to flow again, once a fuse disconnects, it must be discarded and replaced with a new fuse.

Resonator: Resonators are used to either generate waves of specific frequencies or select specific frequencies from a signal.  Think musical instruments.

Relay: Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical.

Reed Switch: Is an electrical switch operated by an applied magnetic field, it could detect the opening of a door.  Think burglar alarm.

It is evident I need to gain a greater knowledge of circuit diagrams.  For the Competency module I am developing knowledge in digital circuits.  This will include more complex circuit diagrams that I will have created using Circuit Wizard but too show that I can interpret them I will also be producing the circuits on breadboards to see the circuits physically working rather than simply just being simulated through software.


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