Electronics is Fun

Below is a simple circuit that demonstrates the use of a transistor.  The transistor drives an LED from a photocell at the input bias circuit. The intensity of the LED light depends upon the intensity of the light from the environment (ambient light) hitting the photocell. The greater the  ambient light, the greater the LED intensity. If light is totally blocked on the photocell, very little or almost no glow coming from the LED. Figure 1                                         This simple circuit can be expounded for many exciting applications in the real world. The photocell is just one of representations of sensors one can use to control the output of the transistor.  The output can be other than an LED, say a motor whose speed can be variably controlled, or it can be an input to another circuit that does some other functions that depends on the input from the sensor. Basic Operation: The photocell has resistance that ranges from 5k (strong light) to 20k (dark).

In the first part of the series we made an introduction about the noise and how we can categorize them into device noise, emitted noise, and conducted noise. We first discussed about the most common noise, the Johnson noise coming from a resistor . This noise is also a white noise, due to the fact that it is present at all frequencies. This noise is produced whether or not a resistor is connected in a circuit. When a resistor is connected to a circuit, say to an amplifier, this resistor will be a source of noise to the circuit. Let's take an inverting operational amplifier as an example that has two resistors connected to it, one at the input and the other one as feedback. The noise due to the resistors can be modeled as noise sources in series with the resistors. Figure 1 Resistor Noise In order to appreciate its effect in the circuit, we must be able to understand how these noise affect the behavior and output of the amplifier. Modeling the noise sources as in the f

I am back from a little hiatus. I've been meaning to write something about noise in the circuits, because I know it's one of the least understood topics in electronics. It's something that one can easily attribute to when something goes odd in the circuit, yet so few have the courage to delve into it. In audio applications, it's easy to describe what noise is. We know if the music is clear and pure, it is free of noise. Anything that is unwanted we can call noise, well, in a broad sense of the word. Noise comes in different forms and from different sources, but in the hope of making some order out of chaos we can attempt to categorize them in the following: 1. Device Noise - noise coming from active and passive devices 2. Emitted Noise - those coming from power lines, motors, radio trasmission, etc. 3. Conducted Noise - those that are already in the circuit, either from the device or transmitted into Electronics components are indeed sources of noise in the ci