Posts tagged: wearable computing

Jul 20 2012

Identifying meaning of “HD” pin on LCD viewfinder

I’m aiming to finally build a wearable, and managed to find a cheap alternative to cutting a set of video glasses in two for a monocular. I got a broken analogue video camera off ebay that had a colour LCD viewfinder. It was a bit of a gamble that being analogue it would have simpler inputs than a digital camcorder, but it paid off. I received the camera today, pulled it apart and got it running on it’s own. 0.2A @5v with composite PAL input.

There’s a 4th pin on the connector though, in addition to Gnd, 5v and video. It’s marked “HD” on the viewfinder PCB, and I traced it back to the IC where (after going through a SMD transistor) connects to the “HD” pin 30 on the controller IC.

The datasheet for the IC expands it a little that the HD pin is for “HD pulse output”, but I can’t find anywhere that explicitly states what the HD pulse is.

I’m *guessing* it’s something to do with the frame timing since the only other HD I can find in the sheet relates to “Horizontal Direction”.

The IC is a Sony CXA1854AR by the by.

The camera supplies the HD pin on the connector with 4.3v however, or at least seems to. I thought I tested it for voltage with the display disconnected, but I’m not sure now. Rather sleep-deprived.

In any case I’m thinking it’s either a case of the IC pin using the transistor to pull the connector pin low, or more likely now that it’s actually a 5v output and my multimeter detected it at only 4.3v due to the duty cycle of the HD pulse. The HD pulse presumably would be something to sync with the video or on-screen text display. But it seems to display PAL video with no problem when it’s not in use, so unsure.

Really I’d just like it if someone can put my mind at ease on the subject. It doesn’t seem essential, but I’d like to know what it’s supposed to do.

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