U2, in your ESP32 8 Relay Board project, is designated with the MPN (Manufacturer Part Number) ULN2803ADWR and is produced by Texas Instruments. This component is an 8-channel Darlington transistor array. The function of U2 within your circuit is quite crucial, especially considering its use in driving relays and handling currents that the ESP32 cannot directly manage due to its lower current output capabilities.
Here's a detailed breakdown of U2's role:
Inputs (I1-I8): Pins 1 through 8 are the input pins, each corresponding to one of the eight Darlington pairs within the IC. These inputs are connected to the ESP32's digital I/O pins (D2, D4, D5, D13, D18, D19, D21, D22), allowing the ESP32 to control the state (on/off) of each relay by setting the respective input pin high or low.
Outputs (O1-O8): Pins 10 through 17 serve as outputs from the Darlington pairs. Each output is connected to one side of the coil of the respective relay (RLY1-RLY8), enabling the relay to switch when the corresponding input is activated. The outputs effectively boost the ESP32's signal to drive the relay coils, which require more current than the ESP32 can provide directly.
Common (COM) - Pin 18: This is a common pin for all the built-in diodes intended for flyback diode protection. Connect this pin to the voltage supply of the relay coils (+5V in this case) to protect the Darlington transistor array from voltage spikes generated when the relay coils are deactivated.
Ground (GND) - Pin 9: This pin is connected to the ground of the circuit, establishing a common reference point for the transistor array's operation.
U2's addition to your circuit mitigates the need for separate transistor and diode arrangements for each relay, simplifying the design and reducing the PCB space required. By utilizing the ULN2803ADWR, your ESP32 can control up to eight relays with minimal direct current draw on its I/O pins, safely interfacing with higher current/voltage loads than it could alone.
The Relay specified in the project is the SRD-05VDC-SL-C, which is a type of Songle Power Relay. This specific relay operates with a coil voltage of 5V DC. However, it has a contact rating typically for switching or carrying circuit of 10A 250VAC/10A 125VAC/10A 30VDC.
So, this relay is not suitable for directly switching 400V. You would need a different relay which is rated for the higher voltage. It's always important to use components within their specified ratings for safety and performance reasons.
Apologies for the confusion, but I'm unable to provide real-time data on the availability and pricing of electronic components.
Nonetheless, I can guide you through the initial steps to help you search for the parts yourself.
When dealing with switching operations at 400V, typically, commercially available power relays capable of switching and withstanding mains voltage are suggested.
For example, you might want to consider the Omron G5LE series or the Panasonic HE series. The "Omron G5LE-14 DC12" and the "Panasonic HE1AN-P-DC12V" are known for their reliability and can manage 250VAC at 10A, with various coil voltage options.
Please check the datasheets beforehand for any relay you opt for, to make sure it suits your particular requirements. When dealing with high voltages, it's crucial to follow safety guidelines.
Inventory may vary, so an ideal strategy would be to visit electronics components supplier websites like Mouser, DigiKey, or RS Components. You can then use their search filters to locate a relay that fits your necessary parameters (400V, current rating, control voltage, single-pole or double-pole, normally open or normally closed, etc.).
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