Sometimes we need to control or drive a high voltage and heavy current load by a small voltage signal. For example, if you want to control water motor with your microcontroller output. We know that microcontroller gives only 5v output which is not sufficient to drive a heavy motor. This circuit, about which this post is, is very-very useful for electronics engineer and hobbyist. So pay attention! For this circuit the material we need is… General Purpose PCB - 5x5 cm. Transistor KN 2222A (TO-92) - 1 No. Relay 5V – 1 No. 1K/0.250W – 2 Nos. 10K/0.250W – 1 No. IN4007 – 2 Nos. LED 3mm – 1 No. Connector – 4 Nos. Few wires. Tools. Concept: Weak signal triggers the transistor and transistor acts as a switch for the relay. You can use any relay of 12V, 24V, 5V etc. but we have to consider power supply or battery we will use. Since 5V power supply is easily available and 9V battery can also be used for 5V output (after using 7805 regulator if needed)....