Electronics is Fun

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...

In the first installment of this series, we talked about what exciting things we can do with just two transistors, in particular BJT transistors. Some of us might probably think that we don't talk a lot about BJT transistors nowadays, not with the thrill, excitement, and trend brought about by high advancements in the technology in the Internet of Things, Machine Learning, Machine Intelligence, Advanced Algorithm, etc.. But we argue that these little circuits and components are constantly in the background of the advancements we see around us and we should not ignore them, as much we will not ignore what we currently enjoy and what the future holds for us. Let's continue to look at the Two-Transistor Series Regulator we talked about in Part 1 . The circuit below is a different version, now using the transistor to provide feedback from the output. This makes the output voltage higher. The output is still derived from the zener voltage. The output voltage is now a s...

Imagine we have two transistors lying on the work bench on a lazy Sunday afternoon and we'd like to do something exciting out of them.  How much can we do out of them? One would be a crude Current Source . You may recall that two transistors assumed to be reasonably matched will produce the same current given the same voltage across base and emitter (VBE). Notice that Q1's base and collector are tied to make the base voltage equal. The programmed current is the supply, 5V, minus ~0.6V, divided by the reference resistor (5V-0.6)/RF..  The reference resistor can be made variable, so that the output current varies. The load can be LED, so that makes it dimmable by adjusting the reference resistor. The current source is certainly not precision, but can be useful in many practical applications like the example shown. Current Source Circuit Another would be a waveform generator, an  Astable Multivibrator . It relies on the capacitor discharging and discharging and t...

In today's age of Internet of Things, machine learning, artificial intelligence, cloud computing, and so on, one might wonder what place the operational amplifier has in the current state of affairs in technology. Is it still really relevant that it's worth continuing to learn them in school or by one's own effort? My answer is yes, and this takes us back to the early beginnings of why the operational amplifier was invented in the first place. To those who are familiar with its history, we recall that it was Harold Black's idea in the early 20th century of negative feedback that the operational amplifier takes it root back to its very beginning. The first Integrated Circuit (IC) op-amp didn't come to us until the mid-1960, as the first operational amplifiers were in the form of vacuum tubes and discrete components. In the early days of amplifiers in the beginning of 1900's, these devices are notoriously non-linear and distorts a lot in telecommunication...

Arduino boards have I/Os (Input/Output) that can either receive or transmit signals. One of its basic functions is digital input/output. It can be programmed to output digital signals that can be used drive devices, such as an LED . To drive an LED, you will have to add a resistor to regulate the current to the LED. The digital output is about 3V (5V or a little less for 5V board), and for an LED the forward voltage is about 2V. What is left (1V) divided by the resistor sets the current. Current is typically 10 to 20mA. Driving an LED Below is an example code for alternating LEDs on Arduino Pro Micro Board. It uses pins 2, 3, 4, and 5 as digital outputs. My 11 year old son helped out in the programming. :) void setup() {   // initialize digital pins 2, 3, 4, and 5 as outputs.   pinMode(2, OUTPUT);   pinMode(3, OUTPUT);   pinMode(4, OUTPUT);   pinMode(5, OUTPUT); } // the loop function runs over and over again forever void loop() {   di...

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. ...