New Discohat design

There is a new version of Discohat in the works. The previous one suffered from reliability issues due to ghost triggers of the GPIO pins and corrupted 40-pin header.

The ghost triggers are very common due to the was Raspberry Pi is designed. GPIO pins have no real hysteresis and therefore when the voltage changes the GPIO pins may fire rapidly. Typically we would get one ghost trigger about once in every 2 hours. The remedy was to use software to read the pin again 3 times to see if the state really had changed. But in the new design I decided to use Schmitt trigger hardware for all input pins. This should work reliably.

The 40 pin connector had a clever design that allowed you to use Discohat on 26 pin units and 40 pin units. But the bad thing was that it was not relieble. Sometimes the contact was flimsy and it affected the operations. To fix this the new Discohat comes with soldered 40 pin connectors that are stackable.

The reason I need stackable 40 pin connectors is to use dedicated audio boards with Discohat. You can of course just use the 3.5mm socket with default audio. But sometimes you need audiophile quality. My problem has been humm sounds caused by connecting audio with common ground. So I did get a floating audio card where the sound is completely isolated from the power of the pi. With floating audio and balanced XLR cables the sound should not have much noise. At the same time the sampling frequency of the audio is 92kHz to allow for a little better quality overall. Obviously you can use any kind of audio. It depends on your needs.

The new Discohat is still optically isolated from the Raspberry Pi. This is to eliminate static noise that is always present on stage due to hot lights, nylon clothing and long wires.