Amp It Up!

Description: This tutorial demonstrates how to create a small relay interface board that allows U4x1 devices to control circuits requiring higher current or voltage than the U4x1 devices can provide directly. It is designed for users of U4x1 devices with custom software or Home Domination. The design can be implemented as presented or serve as a foundation for more complex applications. U4x1 devices have limited current output capabilities when their I/O lines are configured as outputs and should not be connected to voltages exceeding 5V. A relay facilitates the control of devices with voltage and current ratings beyond the U4x1's capabilities. The relay in this design can handle circuits up to 30V (maximum) and 1A (maximum). The 5V relay coil draws approximately 40 mA of current supplied by the Darlington switch in the 2803. This application consists of a small circuit board with screw terminals to interface with a U401 or U421 and the controlled circuit, the 2803 driver, relays, and relay state indicating LEDs. The developed card provides four channels of relay control, with the schematic illustrating one of the four relay-LED channels. The 2803 establishes a switched connection to ground, allowing current to flow through the relay and activate its contacts, which also turns on the associated LED. The relay board can be assembled in various configurations, and a custom printed circuit board (PCB) design could be created using a PCB layout program. However, point-to-point wiring on a simple prototype PCB board was utilized for this application. The board features a "sea of holes" with one-tenth inch spacing, compatible with the leads of the selected components. The assembly photo shows all components before assembly, including a short piece of Wire-Wrap wire used for point-to-point connections. The components used are standard items typically kept in stock for prototyping. The specific types of DIP sockets, resistors, and LEDs are not critical to the design, allowing for flexibility in component selection. Relays appropriate for this application can be sourced from various vendors, with the NAIS TQ series relays being used, specifically the TQ2-5V model. The green screw terminals in the photo have 1-inch lead spacing. A small precision screwdriver is recommended for these terminals due to their size. The relays and terminal blocks can be obtained from Digikey, with specific part numbers provided. Alternative relays, such as the Omron G6DS-1A-DC5, can switch higher currents (5 amps) but may not fit the same DIP sockets. Relays requiring a coil voltage higher than the 5V supplied by USB will necessitate an additional power source. For instance, using a Panasonic DR-12V relay would require adding another screw terminal for the 12V coil supply. The coils for the relays are controlled by the 2803, and the maximum current that the 2803 can switch is specified in the manufacturer's data sheet.

This relay interface board design is particularly useful for applications where the U4x1 devices are employed in home automation or custom control systems. The relay allows for the safe switching of higher voltage and current loads, protecting the U4x1 devices from damage due to excess power requirements. The board's modularity and the option to customize the components make it suitable for a wide range of applications, from simple relay control to more complex automation tasks.

The schematic diagram of the relay board includes connections for the U401 or U421 devices, the relay driver circuit using the 2803, and the relay outputs. Each relay channel is equipped with an LED indicator, providing visual feedback on the relay's state. The design accommodates multiple relay configurations, enabling the user to expand the system as needed.

When constructing the board, attention should be paid to the relay specifications, ensuring that they meet the voltage and current requirements of the intended application. The choice of relay type can greatly influence the performance and reliability of the circuit, particularly in high-load scenarios. Additionally, ensuring proper grounding and power supply connections will enhance the stability and functionality of the relay interface board.

The use of standard components simplifies sourcing and replacement, while the flexibility in design allows for adjustments based on specific project needs. Overall, this relay interface board serves as a practical solution for integrating U4x1 devices into circuits requiring higher power, making it a valuable addition to any electronics toolkit.This tutorial shows how you can build a small relay interface board so that you can use the U4x1 devices to control circuits that require more current or a higher voltage than what the U4x1 devices can provide directly. This tutorial is meant to help anyone using the U4x1 devices with custom software, or with Home Domination.

The design can be imp lemented as is, or it can provide a starting point for more complex implementations. The U4x1 devices have a limited ability to provide current when their io lines are configured as outputs. The io lines should not be connected to voltages higher than 5V. A relay provides a way to control (switch on or off) devices with voltage and current ratings that are greater than the capabilities of the U4x1.

The relay in this design can switch a 30V (maximum), 1A (maximum) circuit. The 5V relay coil uses about 40 mA of current provided by the Darlington switch in the 2803. This application consists of a small circuit card containing screw terminals to interface to a U401 or U421 as well as the controlled circuit, the 2803 driver, relays, and relay state indicating LEDs. The card developed in this application provides four channels of relay control. The schematic above shows one of the four relayLED channels implemented in this design. The 2803 makes a switched connection to ground. When activated, current flows through the relay and activates the relay contacts. The LED associated with the relay is also turned on. The relay board can be assembled in many different ways. A specific custom printed circuit board could be designed with a PCB layout program. The PCB could then be ordered from a PCB production house. For this app note, however, I chose to use point-to-point wiring on a simple prototype PCB board. The board provides a "sea of holes" that are on one tenth inch centers. The components that I chose for this application have leads that have the same spacing. Pictured above are all of the components for the example prior to assembly. The yellow wire in the photo is a short piece of Wire-Wrap wire that I used for all of the point-to-point connections.

I didn`t wire wrap the circuit, I just used Wire-Wrap wire to make the point-to-point connections. The majority of the parts are components that I keep in stock for general prototype use. The specifics about which DIP sockets, resistors, and LEDs to use do not matter much to this design. A different size or type of PCB board could be used, larger or different color LEDs, and even different types of relays. Consideration should be made for driving the relays with the right voltage and sufficient current. Parts appropriate for this app note can be obtained from a variety of vendors. The relays are NAIS TQ series relays. The relays that I chose to implement in this design are TQ2-5V. The screw-terminals in the photo above (green) have. 1 inch spacing between the leads. I use a small "precision" screwdriver with these screw terminals, since they are rather small. These relays and terminal blocks are available from Digikey ( ). The relays are Digikey part number 255-1001-5-ND, the screw terminals are 277-1274-ND. Most of the parts (other than the PCB) for this project can be obtained from Digikey. A relay that can switch more current (5 amps) such as the Omron G6DS-1A-DC5 (Z2317-ND at Digikey) could also be used.

This relay has a different form-factor, and therefore will not fit into the DIP sockets. Relays that use a coil voltage higher than the 5V supplied by USB would need to have that voltage supplied by a different power source. Using a relay such as the Panasonic DR-12V would mean adding another screw terminal to the design to provide a source for the coil`s 12V.

The coils for the relays are switched by the 2803. The maximum current that the 2803 can switch is in the 2803 data sheet for the manufacturer of the specific 2803. This defines the limits to the current and voltage o