Check the listing for details. PWR-1 Power Protection and Filtering / 4 Amp DC / 3 Options. Condition: New. Listed at 9.95 USD. Most of us have been there. For whatever reason, and in fact contrary to all reason, you’ve reversed the polarity of your power connection and now one, some, or maybe all of the active devices in your homebrew rig–transistors mostly (including those built into ICs)–are toast. All of us have been somewhere else, too: the “undiscovered country” of noise conducted through our power supplies. Because it’s very uncommon to shield the power cables we connect to our rigs, a lot of noise is also picked up in them, fed into our power inputs, and then bounces around inside our sensitive circuitry. What’s more, we often generate noise inside our gear, commonly from digital devices such as Arduinos, displays, rotary encoders, and the like. In short, we’re happier when we can either eliminate or reduce noise sources–certainly those over which we have some control. This is where the PWR-1 comes in. Its P-Channel MOSFET instantly shuts off power if polarity has been reversed, and its low-pass and common-mode filtering keep noise down to a tolerable level. Some circuits–such as a direct-conversion receivers–are susceptible to common-mode AC hum. The PWR-1 suppresses that to inaudible levels. The PWR-1 has one other optional function: it can sense the total current draw through it, sending an analog signal that can be read by the ADC input of an MCU (Arduino, Xiao, etc.). This is done with a Hall-effect sensor, so full voltage and current are available. In fact, the PWR-1 will be available in three versions: one with just the fuse and reverse-polarity protection, one to also include noise filtering, and one for the whole . . . enchilada. Each will be available only as a kit.