Latching Relay Module With Physical Button Input and Arduino Compatible Inputs

In electronics, a device is said to be a latching device if it maintains any particular fixed state even after removal of the input signal. The same also applies for electronic/electromechanical relays. Basically the electromechanical relays that are used today are of two types:

1. Non-Latching Relay : These relays are most widely used where energy consumption is basically not an issue.This type relay(s) comes back to its original state once the input signal is removed.

2. Latching Relay : These relays are mostly used in automobiles and are rarely used for basic prototyping needs.

Most of the relays which we use today are monostable relays, that means it has only one stable state and so it is called non-latching relays. You must have heard about N.O (Normally Open) and N.C (Normally Closed) terminals of a basic electromechanical relay. However these terminals which are present over the relay show that the electronic relay which we are using has only one stable state.

here i developed a fully functioning pcb ready to be produced and used

all files are provided and are open source

COMPONENTS REQUIRED:

1. 1x Small Size Perforated Circuit Board
2. 1x 3 PIN PCB Mount Screw Terminal
3. 1x 5V-DC 240V, 50-60Hz, 5A SPDT Relay
4. 3x BC547 NPN Transistor
5. 2x Small LEDs (Different colors are recommended.)
6. 2x 330ohms Resistors
7. 2x Momentary Push Button Switches (Different colors are recommended.)
8. 1x 1N4007 General Purpose PN Junction Diode
9. 1x NE555 Timer IC
10. 4x Male Header Pins
11. 3x 10Kohms resistors
12. 2x 15Kohms resistors

TOOLS REQUIRED:

1. Soldering Iron
2. Soldering Lead Wire
3. Soldering Flux
4. Multimeter with Probes
5. A strong Adhesive

The circuit diagram shown above illustrates the relay module setup. It’s essential that all components are connected exactly as depicted in the diagram to ensure proper functionality.

This circuit is an implementation of the NE555 timer IC, configured as a latch or 1-bit memory cell, commonly known as an SR (Set-Reset) latch. In this configuration, the relay's **Set (ON)** and **Reset (OFF)** states can be controlled either by pressing momentary push buttons or by applying 5V logic inputs to the **SET** and **RESET** pins. This dual-control mechanism offers flexibility in the way the relay operates, making it ideal for a variety of use cases where manual or automated control is needed.

Functionality of the SR Latch

1. The NE555 timer in this setup functions as a bistable multivibrator, meaning it can store and maintain one of two states (Set or Reset). The state remains stable until an input signal is provided to change it. Here, we are using an **SR latch** configuration where:
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3. SET input- turns the relay ON, activating its Normally Open (N.O.) terminal, which closes the circuit and allows current to flow through the connected load.
4. RESET input- turns the relay OFF, returning it to its Normally Closed (N.C.) state, which opens the circuit and stops current flow to the load.
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6. These inputs can either be provided by physical switches (momentary push buttons) or through logic-level control signals, such as those from a microcontroller or any other 5V logic device.

Inputs and Terminals

1. Pin Jack J1-: This is the input terminal block, used for power and control inputs. It accepts the following inputs:
2. - VCC: A 5V DC power supply. This can be easily sourced from a USB port, making the circuit highly portable and compatible with standard 5V systems.
3. - GND: The ground connection, which serves as the reference voltage for the module.
4. - SET INPUT: A control input for turning the relay ON. A voltage greater than 0V at this pin activates the relay, switching it to its ON state.
5. - RESET INPUT: A control input for turning the relay OFF. A voltage greater than 0V at this pin deactivates the relay, switching it back to its OFF state.
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7. - Pin Jack J2: This is the output terminal block consisting of a 3-pin screw terminal. These pins provide the output connections from the relay:
8. - Common (COM): The central terminal connected to the load.
9. - Normally Open (N.O.): This terminal is disconnected when the relay is in the OFF state and connected when the relay is turned ON.
10. - Normally Closed (N.C.): This terminal is connected when the relay is in the OFF state and disconnected when the relay is ON.

Key Operational Notes

1. - Set and Reset Behavior: The SET input will turn the relay ON, while the RESET input will turn it OFF. These two functions should never be activated at the same time. If both SET and RESET signals are applied simultaneously, the relay will default to the OFF state. This is due to the nature of the SR latch, where simultaneous activation leads to an undefined condition, but the circuit has been designed to prioritize resetting the relay.
3. - Portability and Flexibility: The module's power supply can be easily sourced from a USB port or any 5V DC source, making it suitable for portable applications. Its design also allows for integration with various digital systems, such as Arduino or Raspberry Pi, providing logic-level control over the relay.
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5. - Versatility: This module can be used in various projects where relay control is needed. From basic prototyping to automation systems, the ability to control the relay through both manual buttons and logic inputs expands its usability. It offers reliable state control for a wide range of applications, including home automation, robotics, and automotive systems.

By following the circuit diagram precisely and understanding how the inputs work, you can effectively create a versatile relay control module that behaves as a bistable latch, ensuring stable ON/OFF switching states based on your desired input control.

ADVANTAGES:

The advantages of this relay module as compared to the conventional relay module are as follows:

1. Unlike the normal relay modules which mostly work under specific logic input voltage such as 5V or 3.3V, this relay module can accept a wide range of input voltage or current signals to control the switching action.

2. The latch mechanism of switching is usually used in controlling circuits which have unstable (pulsating DC) or time varying input signals.

3. Wide range of operating voltage- One can easily use this module with any relays which have coil voltages starting from 5V to 18V. Depending upon the coil voltage, one can supply the VCC voltage accordingly.

4. The state of the relay is stored even after the control input signals are removed.

CONCLUSION:

This relay module just provides a new way to control the relays. Not only this can be used to control electromechanical relays but also it can be used to control solid state relays.

Basically this relay module is an upgrade over the existing relay modules and provides various features and functionalities.

⚠️ Disclaimer:

The information, content, and features provided herein are offered "as is" with no warranties or guarantees. Utilization of this project, design, or product is solely at your risk. Adherence to safety guidelines and comprehensive testing prior to deployment is advised. The creators will not be held responsible for any damages, injuries, or losses incurred from the use, modification, or replication of this work. The work has been tested and deemed satisfactory for similar and intended use cases.

Exercise caution and handle all electrical connections, components, and power supplies with care.

gerber file : click here to download