This universal relay board will allow you to drive a 12-volt DPDT relay using heat, cold, light, dark, sound, logic-level voltages, and just about any varying resistive output sensor you can think of. In fact, you can use it to switch the relay ON or OFF using any voltage between zero to 12 volts DC or any sensor that has a varying output in this range. This is the ultimate relay board. It could even be made to run on six- or 24-volts DC with a few resistor changes and the availability of the appropriate voltage relay. I set out to design this project with simplicity in mind; I wanted to keep the component count to a minimum and to use the same value components for all configurations available. Size was also a factor — the smaller, the better. There are heaps of similar individual circuits around in kit form, in books, or on the Internet, but none that integrates everything and allows the user the flexibility that this circuit does with a minimum of fuss.
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