![]() In this circuit, High signal activates/turns on relay switch. There is a small chance that his module is actually High level triggered, as shown below. I am only making an educated guess that the OP's relay is low level triggered. That is why the " JD-Vcc jumper" coming in, to do "Total Optical Isolation" (More about his later). Noise usually also goes through the ground wires. An " optical isolator" is usually used to prevent/reduce EMI (ElectroMagnetic Interference) noise going back to the signal source (Raspberry Rpi). ![]() Real circuits must have a " flyback diode" to absorb the energy of flyback current when switching off energizing current. The over simplified schematics give a rough idea of the operations of High and Low trigger circuit. To explain the idea of Low and High trigger relays, let us start with the no optical method and look the the respective schematics below. Part A - Simple High and Low level trigger relay modules without optical isolation The long answer below describes the JD-Vcc circuit in detail, starting from the most basic ideas of High and Low trigger relays with and without optical isolation. The simple wiring and operation described in the short answer above does not involve the JD-Vcc jumper which is a very clever electronic circuit design. Part F - Discussion and Recommendation - / to continue. Part E - Using The JD-Vcc Jumper for Total Optical Isolation / to continue. Part D - Confusion between JD-Vcc jumper and High/Low Level Select Jumper Relays Part C - Boot time Relay Module Status, relay switch spec and misuse of NC terminal Part B - High and Low trigger relay modules with optical isolation If signal is High (~3V) then current sinking is too small to activate the optocoupler, therefore Songle switch is deenergized, and relay switched off.Ĭontents Part A - Simple High Low Trigger Relays Without Opto Isolation If signal at IN is Low (0V, Ground), then current flows (sinks) from Vcc to IN, optical coupler EL817C is activated, Songle switch is activated (energized), contact COM is connected to NO (Normal open). Using the 3V3 Raspberry Pi (or 3V3 Arduino) as an example, The Songle relay switch power is from external 5V power source, Vcc is connect to Rpi's 3V3 logic power, and IN is connected to an Rpi GPIO pin in output mode. One very simple wiring method is shown below. The OP's 4 channel relay module is " Low Logical Level Triggerable" (Low Trigger) with the " JD-Vcc jumper" to suit different configurations of relay power and control signal levels. A case with Rpi powered by a battery, the Rpi's ground can be "floating" and not connected electrically to the relay module. ![]() ![]() No electrical current ground is used for reference. Rpi Vcc sources current through 1k to the LED which inputs optical signal to the opto transistor on the other side. (2) However, for this "total opto isolation configuration", the Rpi ground should not be shorted to the external power ground, because the Rpi uses the optical coupler independent of any part of the electrical of the relay module. (1) Usually if an external power supply for the relay module, it is important to short the Arduno/Rpi signal ground with the external power ground, so that Rpi signal has the common ground with the external power supply ground. My original plan was to draw the redundant wire, and then crossed it out with the following: I agree that this shorting to ground wire is misleading and causes confusion. Many thanks to fantasist for pointing out that in the schematic of the short answer below, "the short circuit ground wire is redundant". What is it and how to use it?Īcknowledgement and Update 2020nov01hkt1609 The module has a yellow jumper at the bottom right, marked JD-Vcc. The OP has a 4 channel relay module similar to one shown below. Thank you very much for pointing me to this one, that seems to be the right one: My module is generic, and I couldn't find the official schematics. I tested with the multimeter and all the pins I connected are getting power, so either I am missing something (very probable) or I both boards are brokenĪnother thing i noticed is that if i apply 5v and GND, then all IN seems to have around 3v I also tried 3v instead of 5, and connecting to another Power supply the JD-VCC. The module seems to have some LEDs to indicate when the relay should be on, they do not light. I was expecting the first relay to switch, but nothing happened. My first try was using a breadboard 5v power supply, connecting VCC and In1 to 5V and GND to GND. I got two 4-relay-modules and I am probably doing something wrong because none of them seems to work: Check the full answer to understand why :) A quick benefit of JD-VCC, is that allows you to control the relays that are 5V with 3.3V GPIOs.
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