How LDRs, Transistors, and Flip-Flops Work

How LDRs and Transistors Work Together

LDR Circuit States and Behaviors

• No light (LED is off): The LDR has high resistance. There are two paths; the path with less resistance passes more electrons. As there is little current, the transistor does not admit this current and does not feed the base of the transistor (current does not pass from the collector to the emitter).
• Light is present (LED is on): The LDR has low resistance. This low resistance allows the current to pass and feed the base of the transistor, which turns on the LED. (When the LED is on, if we cover the LDR, the LED turns off).
• No light (LED is off - alternative state): In the LDR, there is high resistance, and the LDR steals the base current of the transistor, so current does not pass.
• No light (LED is on - alternative state): There is a lot of resistance in the LDR, but the current prefers to go to the negative electrons through the transistor.

Understanding Robbing Current

At the base of the first transistor, current is lower, and it is extinguished. When electrons pass through the switch connected to the negative terminal (battery) for a few moments, it gives a boost to the other transistor, causing it to run. (The first LED is lit, and when I turn on the switch, the other one lights up).

The Flip-Flop Circuit and 1-Byte Memory

The path with a resistance of 22 kΩ wins the race because it has more strength and is the first to reach the base of the transistor, as its resistance value is lower. It reaches the base first and robs the current from the other one. We remove the connection, and it runs on the base since the current was negative through the switch and the base current. At that moment, the other transistor and resistor win the race. This movement acts as a 1-byte memory that stores information (like a change in a byte).

Key Electronic Components Defined

• Transistor: A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit.
• LDR (Light Dependent Resistor): A light-dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity. A photoresistor is made of a high-resistance semiconductor. If light falling on the device is of a high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band.
• LED (Light Emitting Diode): A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting.