About Me and this Blog

My name is Darwin. Electronics is my passion, and I love sharing my passion to others, technician, hobbyist, or an engineer. If you browse through this blog you will find that topics are not in any order but rather out of the common questions one might have. They are randomly picked and can cover topics from the basic concepts to practical circuits one can use.

Comments and feedback are welcome in this blog.

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What Can You Do With Two Transistors (BJT)? Part 3

This is a continuation of a running series on the kinds of simple circuits we can do with basically just two transistors. In Part 1 we talked about Current source and Multi-vibrator, and in Part 2 we discussed Linear Regulators. We will continue with more practical circuits that can be very useful in many applications. There are instances that we would like to translate a digital logic voltage from one level to another, say from 5V to 3V, or vice-versa. The input perhaps coming from a circuit that has a higher logic level that needs to input to a different logic level. For a single direction of signal, a single transistor would be enough. Bidirectional functionality can be achieved using two transistors, Bidirectional Logic Translator , as shown below. R1 serves as a pull-up resistor to 5V in the circuit. The input typically comes from an open-drain or open-collector output, pulled up to supply by R1. The enable pin should be tied to the lower of the two supplies. Whe...

Arduino Transistor DC Motor Control

Arduino boards have PWM (Pulse Width Modulation) outputs that can be used to control like the speed of a DC motor. On a Pro Micro, those outputs are encircled white on the board. You can program it such that it outputs on a scale of 1-255, 1 being the slowest and 255 being the fastest. PWM gives out pulses whose width is varied (modulated) while the period is constant. The longer it is high, the higher power it delivers to the circuit. PWM can be used to drive a transistor (switch) which in turn drives the motor ON and OFF. The longer the switch is ON, the higher the power delivered to the motor, and thus faster. The circuit consists of a transistor Q1 (TIP31) NPN transistor, driven by the PWM from Arduino. The resistor is to limit the current to the base, but enough to operate the transistor in saturation when the input is high. The diode is to protect the motor from any back emf that might come from the motor when the current is cut off. The circuit is supplied by a 9V battery. ...

Resistance, Capacitance, and Inductance (R-C and R-L Circuit)

Our aim here is to discuss the very important concepts and give intuitive explanations of the subjects. We'll start with the resistor which is the most straightforward, then with the less understood and often misunderstood concepts of capacitance and inductance. We will discuss the R-C and R-L circuits as well. These along with Ohm's Law, Kirchoff's Voltage Law (KVL) and Kirchoff's Current Law (KCL) are the very foundations of understanding the complete behaviors of practically any circuit one might encounter. Resistance It is a general term that refers to the opposition to the free flow of current in a circuit. More accurately, it refers or applies to DC (direct current). Resistance doesn't apply only to resistors but also to a host of other components in the circuit. For example, a copper trace has a resistance according to its dimensions, as well as the leads of he components.When a current flows through a resistor a potential difference is generated acr...

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