After the Advance Acoustic style streamer project build earlier this year, I got a request from a friend to build him a streamer matching the style of his Harman Kardon audio system.
The base was found in an old defective HK amplifier. We stripped the case from all electronics and removed the front panel. A new front panel was designed and cut with a laser cutter. A 11.9" Waveshare touchscreen is used on a Rpi 4B, 2 Gb with an IQ audio DAC Pro. A separate 15W power supply for the touchscreen was combined with an ultra low noise PS on dual Talema toroid transformers. The encoder knob is for selecting prev/next track when turned or play/pause when pushed. The power button on the left powers the unit on and off. In off state, it is in standby mode and uses very little power.
Again, thanks to @Gelo5! On base of his excellent graphic examples and code a HK matching design was made for the Screensaver-Peppymeter.
Soon starting on an old school Rotel style streamer project!
Nice to hear you are working on a Emotiva style streamer. That will not be an easy project!
I used the standby/power relay board from the old HK amp we used for the casing.
This is a board that provides you with a low power 15v DC voltage from a small PS and a switch input. When you provide this input with a 4.3V voltage, the board switches the power on over a relay on this board. With this standby/power relay board you now have a base for switching the power on the power supplies for your Rpi eg.
To the switch input of this board we have connected a small delay relay board (Aliexpress) that is triggered from one contact of a push button (power button). When triggered it will provide you with a 5V voltage for a certain amount of time. The output of this delay is connected to the input of the standby/power relay board over a diode. This will switch on the power for the duration of the delay that has been set. The Rpi will now power up and after a moment will provide you with a 5V voltage on the USB outlets.
This Rpi USB voltage is over a diode connected to the same switch input of the standby/power relay board. By doing this, the power relay board will hold the relay and provides power to the Rpi as long as the USB voltage is present.
The moment you close the Volumio software the Rpi will shutdown and the moment the USB-voltage drops, the power will be switched off.
By a second switch contact on the power push button, that is connected to an input of the Rpi and ground, the Rpi gets a signal on a GPIO to power off. The GPIO input plugin is used to manage this.
I do have circuit diagrams made for the above. Let me know if they could be of use for you.
Thank you for your comprehensive explanation. If you could share the diagram, that would be great. I found a ready-made StandBy module for my device:
Unfortunately, it does not solve the problem of switching off the device from the Volumio application control level (it does not switch off the device’s power supply when you press ‘Shut Down’). I am looking for a solution to this problem, which is why I am interested in your solution.
Once I have finished the project, I will post some photos.
This is the circuit diagram made for this streamer. It is a little messy drawn, but it was made, so I know how it is wired when I have to work on the streamer in a couple of years from now.
The 2nd part is the circuit diagram of the HK amp standby/power board out of the service manual from this amp.
