# How is the common anode 7-segment display in Ben Eater's setup working?

First question in this community, and I'm a beginner when it comes to circuits. In Ben Eater's video on using an EEPROM for combinational logic, he uses the output of an EEPROM to drive a common anode seven-segment display. It doesn't really seem like it should work the way it does, however.

Here's the setup in question (at the correct timestamp): https://youtu.be/BA12Z7gQ4P0?t=1309

The way I understand common anode to work is that a given segment of the display will only light up if it has a path to ground. In this setup, it looks like every segment has a path to ground from the white wires, through the LEDs, and to the resistors. But when the EEPROM is outputting high on a given bit, somehow the path to ground for that segment is blocked. Isn't there still a path to ground for that segment, though?

# Update

Would this be a correct representation of the circuit? The EEPROM essentially acts like a switch, so if it's open, all current travels through the segment of the LED. If it's closed, then the voltage at both junctions of the segment circuit are at the same voltage, so no current flows through that segment. That would make sense.

• Since you are a beginner, it might be a good idea to reverse engineer his circuit. Draw a schematic , download and read the data sheets. Aug 9, 2019 at 15:31
• Can you share schematics of it.. wiring diagram of it. It will be easy to comprehend Aug 9, 2019 at 15:32
• The EPROM is not a switch, it drives high or low. What is nasty about this circuit is that if you disconnect the EPROM, both the discrete LED and the digit segment may light, unless the sum of their forward voltages is so close to the supply voltage that miniscule current flows. In a dark room you might still see them lighting. That looks like it might be a white 7-seg so it may have a fairly high forward voltage. Aug 9, 2019 at 16:28
• Incidentally this demonstrates why video alone is a horrible medium - such a presentation needs to include static documentation which can be easily reviewed. If someone is going to be irresponsible enough to publish in video format only, the proper place for clarification questions is the comment section of their video. Aug 9, 2019 at 16:32