How are the relays connected to the microcontroller?
As it can be seen from the above circuit diagram, a ULN2003 is connected between the microcontroller and relays in order to drive multiple relays. The input is taken from the microcontroller pins and the output corresponding to each input is given to the 5 relays on the output.
What kind of current does a microcontroller need?
The source or sink current of a pic microcontroller is just 25mA whereas an amount of 50 to 100mA current is required by a relay to function properly. Due to the presence of back emf, the negative voltages can reach the microcontroller and damage it. The above circuit is a relay driver circuit.
How is a diode connected to a microcontroller?
A diode 1N4007 is connected to protect the components against the back emf. This back emf is generated in the coil of the relay when the transistor turns off. The LED indicates the state of the relay; whether it is on or off. A resistor R1 is connected which defines the intensity of the LED.
What kind of transistor is used in a relay?
A typical circuit consists of an NPN transistor switch. The coil of the relay is driven by this switch. Zero or negative voltage on the base of transistor indicates that the transistor is off and no current is flowing.
How does a relay box control high voltage?
The magic device at the center of these boxes is a relay. A relay is basically an electromagnetic switch, and it allows me to control a large amount of high voltage power (10A at 120V) using a tiny amount of low voltage power (~5 mA at 3.3V).
What kind of transistors are used in microcontrollers?
If you want to use more relays, using transistors will be difficult. In these cases you may use ULN2003 or ULN2803. These are monolithic IC s consists of High Voltage High Current Darlington transistor arrays. You can connect seven relays using ULN2003 and eight relays using ULN2803.
How is a relay used in a circuit?
A relay is an electromagnetic switch which is used to switch High Voltage/Current using Low power circuits. Relay isolates low power circuits from high power circuits. It is activated by energizing a coil wounded on a soft iron core. For detailed working of relay please visit this page.