The temperature sensor in a rice cooker with a negative temperature coefficient has a relatively high resistance, sharing most of the voltage. The microcontroller's feedback voltage is relatively low. Upon detecting the low voltage, the microcontroller can initiate cooking and other functions. When we press the cooking function button on the rice cooker, the base pin of the transistor driving the relay receives a high-level signal from the microcontroller, and the transistor is then connected. The relay coil receives 12V DC, and its normally open contact closes. At this time, the heating plate is connected to AC 220V, and the rice cooker enters the heating and cooking state. This is one of the typical applications of a relay in a circuit. What is the function and wiring method of an AC relay?
I. Relay Wiring Method
1. Transistor Output (DO) Wiring Method
Some smart embedded IoT devices support transistor output (DO). The transistor uses a high-power field-effect transistor (MOSFET). A switch or external DC intermediate relay can be used to control AC loads from a household high-power DC load.
2. NPN type output wiring method
The device's terminal screen is VCC_Y, GND_Y, Y1~Y8
The NPN type output is characterized by VCC_Y being connected to the positive power supply, GND_Y being connected to the negative power supply, and Y1~Y8 outputting a low level. The specific wiring method is shown in the figure.
II. Function of a Relay
Relays can be used for adjustment, protection, and switching. I believe the most commonly used relay is the electromagnetic relay; it is one of the important control components in power electronic devices such as automatic control and mechatronics systems. Not long ago, I repaired a smart rice cooker for a friend. The heating plate at the bottom of the rice cooker is energized and de-energized; this is controlled by the normally open contacts of a relay. I drew the circuit diagram below with the wiring. We can see that the relay is driven by a transistor, which is controlled by a PIC microcontroller on the rice cooker's mainboard.
What is the function and wiring method of an AC relay? Relay wiring typically involves using the resistance setting on a multimeter to measure the resistance of its contacts for relay testing. Normally closed contacts should have a resistance of zero ohms, and normally open contacts should have an infinite resistance. When measuring the coil resistance, it should be between 25 ohms and 2000 ohms. Generally, relays with lower rated voltages have lower coil resistance. Relays with higher rated voltages have higher coil resistance. We can use the RX10 range of a multimeter for measurement.
