Previously I wrote how I designed and implemented a 12 Volt trigger for an NAD audio amplifier. Some time ago I also designed a PCB version of it. Here you can find some photos and the Eagle schematic.

There is one error in the design: the GND pin of the Wemos D1 mini board is not connected to the ground plane. I solved it with an air wire.

Some of the differences to the previous version are that it now has a button, a 12V input trigger, and a status LED. The button allows to manually switch it on and off without having to use my mobile phone. The 12 V input trigger allows the amplifier to be switched on by and off by the Sonos Port that is also connected to the amplifier.

I am using Tasmota as the firmware which – besides the button to switch it on and off – allows control over a web interface and over MQTT. The Tasmota template for the configuration is the following: {"NAME":"12V trigger", "GPIO":[1,1, 1,1,32,288,0,1,256,1,160,1,1,1], "FLAG":0, "BASE":18}.

The MQTT interface makes it easy to implement some automation with Node-RED that I have running on a Raspberry Pi. The automation is the following: whenever the smart TV or the MacMini (used for music) are switched on, as detected by them returning a network ping on their IP address, then the amplifier switches on, and vice versa.

I also have it configured using Homebridge in my Apple Home environment, which allows the Home application on my iPhone or iPad to manually control it, besides the Tasmota web interface.

Combining all of these, the NAD amplifier is switched on and off by either

• the manual button
• the smart TV (detected by an IP ping)
• the MacMini (detected by an IP ping)
• the Sonos Port (detected by its 12V output trigger)
• the Apple Home application on my iPhone/iPad
• the Tasmota web interface

However, the automation is not perfect: when after an afternoon of listening to Sonos we switch on the TV and switch off the Sonos Port, the Sonos Port only falls asleep after a minute or so. Consequently, the last action happens to be the Sonos Port 12V output going low; the amplifier therefore switches off after a minute or so, whereas we just switched the TV on. A quick press on the manual button switches it on again. Also, whenever we switch between MacMini, TV, or Sonos, we still have to walk to the amplifier to toggle it to the right audio input. An idea for the future is to mount an IR blaster that switches between the audio inputs automatically.