Amp It Up!

Posted on Feb 6, 2014

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

Amp It Up!
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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...

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