Back in the day, camcorders had black & white miniature CRT based viewfinders at first. At the end of this era, colour LCD viewfinders became available too, but because their resolution was very poor in the beginning, many high-end camera’s stuck with black & white CRTs. Many wannabe-hobby-electronics-engineers harvest these tiny black & white CRTs from old camcorders and show them off on youtube and hack-a-day as if they have just invented warm water.
This particularly small sized CRTs were never made in colour versions, probably due to size constraints of the electron gun. The smallest colour CRT I am aware of is the one in the Panasonic CT-101 portable TV, but that tube is already significantly larger, and still they have to resort to all kinds of tricks to make it display colour.
Around this era I was still in school, studying electronic engineering, and I remember there briefly was a camcorder with an extraordinary viewfinder on the market, combining best of both worlds: CRT resolution, but with colours. The way they did this was by using the same black & white miniature CRT everybody else did, but they combined it with a colour wheel. Colours weren’t brilliant to modern standards, but they were a lot better than the colours and the resolution on miniature LCDs at that time.
After many nights of researching (there isn't much information on vintage 90's camcorders on the Internet) I found out that this camera in my memories must be a Mitsubishi HS-CX6. And with some luck I was able to purchase a working version off of eBay. I cracked it open and indeed, it has a colour wheel. Or better; Colour cone, so save space.
Now I wanted to convert this viewfinder in a little gadget. 3D print an open housing for it, connect a raspberry pi to it and show people how great it is. But unfortunately this viewfinder isn't as self-contained as I hoped it would be. I expected it to take a black & white video signal, containing field data of red, green and blue time-domain multiplexed. Still 50 fields per second, consisting of 16.7 red, 16.7 green and 16.7 blue fields. Simple technologie, no need for memory.
But unfortunately it works differently. De viewfinder runs on 5 volts and received a 4.5 volt DC signal of which I do not know the function. Further more it receives a 50Hz block wave (95% high) which seems to be field sync, and a 15.625kHz block wave (don't recall the duty cycle) which appears to be the line sync. So far so good, but the last signal it receives is really unexpected.
The last signal resembles a video signal, but contains 3 fields between field sync pulses, and 3 lines between line sync pulses. That suggests some memory is involved in time-domain multiplexing three separate colour fields into the time slot of a full-colour field.
Does anybody know a cheap way of doing that? I will post photo's of this viewfinder later.