Recently I’ve been messing around with HDMI cables since I’ve been watching Netflix movies and TV shows on my TV that isn’t smart.
I have noticed that the cables can discern if they’re plugged in or not. If I plug in the cable with my computer off, the TV says “No signal”, and if I disconnect the cable, the TV says “Verify cable connection”. How do the device knows the difference?
I apologize for my poor English.
In: Technology
HDMI devices receive 5v from the source device to power up circuitry in the display device (you can power a device from an HDMI port alone, e.g. Chromecasts, etc. from that 5v alone just by plugging it into the TV, though they often give you a USB cable too).
There’s also an enormous amount of handshaking where the two devices tell each other what they can and can’t do, like VGA monitors used to with EDID.
It’s all old technology, nothing to do with HDMI – many TVs and projectors can detect a signal on even a composite video cable by just the 1v peak-to-peak signal coming down it, and SCART (Euroconnector) is a decades-old predecessor of HDMI, basically, that can carry lots of different signals (audio, composite, RGB, S-Video, data, etc.) and also supplies power on a certain pin if one of those devices wants to show on the screen (which can trigger the TV to turn on, or change channel to that device).
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