A closer look at the RPI studio clock

General Lighting

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As I had to move stuff around in my studio anyway I made this video to show the folk at ICR-FM how to build the opto board as their RPI clock gave up the ghost; most likely because a rough signal was directly connected to the GPIO pins. (RPIs do not like that!)

I will make a sketch of the circuit diagram when I get more time but it is very simple; just 4 x Philips (sorry, Vishay, I am old
) CNY17 optos - the RPI GPIOS are connected so the emitter of each phototransistor is to the GND of the RPI, and the collector goes to the GPIO pin as appropriate.

The LEDs on the other side are connected via a 1k0 current limiting resistor to L+ and the cathode to GND of your signalling / control wiring.

when a control voltage is applied to each CNY17 it lights up the LED inside and the phototransistor connects the GPIO to GND and signals to the RPI; but the two systems are completely isolated from each other (up to about 1500 volts!). Optoisolators are used in lots of things for this purpose (including the power supplies in many PCs)

You can take the control voltage from existing low voltage studio signalling controls such as a 12V feed to a LED "on air" lamp elsewhere in the studio (I am just using a 6 volt battery as a test) - (don't use the strong voltage directly from the 230V mains!)