Modular Power Supply Progress 2

I’m tinkering around with a video switch for the Power Supply. The simplest idea I can think of is using an Open Collector switch using Transistors.

I have bread boarded up a simple circuit that is nothing more then a 1K Ohm resistor on the base of a NPN 2n3904 Transistor. Around 0.7 Volts on that current limit resistor is enough to make the Transistor switch on.

Instead of using several of these Transistors I can use a simple IC. The ULN200x Series will work. This is an simple Transistor array typically used for Stepper Motors but still would work in the application. I can also use a DIP Resistor array as well.

It will share a common ground and I would just have to switch the Video Pin to High or Low.

For a example say I am using the Terminal to Control it. I would issue a “CHAN1” command and it would switch off all four outputs and put the output pin for CHAN1 high and I would have a display for that channel.

Now if I really want to get fancy I could toss in a LM1881 and have an On Screen Overlay. This way I can have a Marquee/Banner on the Master on at all times and just have the Slave pump the info in.

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