From: fmg@alpha.smi.med.pitt.edu (Filip Gieszczykiewicz)
Newsgroups: sci.electronics
Subject: 3 "things" on one cable
Summary: video, control, & power on coax (a bit longish)
Date: 9 Jan 93 08:32:55 GMT
Followup-To: sci.electronics
Organization: Medical Informatics, Pittsburgh, PA USA


	Greetings. Looking for *practical* references and ideas on the
	subject of transmitting video, control signals (2-way), and
	power on a single-conductor coax cable.

	The video will be of the "composite" format (not all that high
	bandwidth) and will originate in a standard camcorder. The 
	quality need not be high since it will be used only for remote
	navigation - the camcorder will be instructed to record any
	scenes of interest on tape.

	Description follows but if you're not interested, hit "n" now.


	The application is a home-made underwater "droid". I've had the
	idea kicking around in my mind for a while and only now have
	the camcorder prices come down to where I may consider risking
	my investment :-)

	The second reason is that, while vacationing in the Florida Keys
	these past holidays, I met a man who did the impossible. I was
	windsurfing and saw a bunch (4-10) DIVER flags in the water and
	a guy in a small boat staring at a small TV with his hands on
	strange controls - you bet I investigated ;-)

	His baby consisted of a normal VHS camcorder in a special case
	made of Lexan(tm). Let me describe it in a bit more detail - in
	case anyone else cares:

	1) He used both plaxiglass (1/2") and Lexan(tm) in the design of
	   the case. The case is more than just a simple box. Since he
	   used a standard camcorder, he had to mount a bunch of gear-
	   motors and solenoids to operate the various switches and the
	   zoom and focus (since IR bounces off the enclosure) rings.
	   From closer inspection of the case, I could think of a number
	   of ways to improve it. His construction did not permit the
	   opening of the case in the field since it was sealed temporarily
	   with silicone and had to be pryed (sp?) off at the work-bench.
	   His reasoning was that since the camcorder has a 3HR capacity
	   (on SP mode), it would be quite sufficient for his purposes.

	2) He said that he used gell batteries inside the case for power
	   because this eliminated the need to transfer the power via
	   the coax he was using for both the control and video signals.
	   He had a small 6V 4AH battery for all the solenoids and micro
	   8051BASIC (!!) and a large 12V 35AH battery for both the cam
	   and all the "fans". If both batteries "died" for any reason,
	   and the coax broke, a solenoid would release a wired (with
	   fishing line :-) ballast weight and the case would slowly come
	   to the surface. He said he never had to use this "feature".

	3) He said that he wrote a small program in BASIC for the micro
	   on-board the box that allowed him to send control and navigation
	   commands via a terse serial protocol (I didn't ask him to
	   explain - I was more interested in the hardware - shoot me ;-)
	   In all, he said that it worked because the video signal
	   did not interfere with the slow speed serial channel (2400
	   baud?). This is what I'm interested in - how do I do this?
	   Can I just use a isolation transformer to block the serial (DC?)
	   signals from the video? It can't be THAT simple - what's up?

	4) The steering was not precise. To be reliable, it had to be
	   REAL SIMPLE... The small DC motors that drive the home-made
	   props were stationary. It was akin steering a tank :-) He said
	   this would be his next year's project - that and writing the
	   BASIC code to make the steering "transparent" (ie. you press
	   the joystick left and it goes left all by itself). I seem to
	   forget how many motors he had (must be from that time I
	   catapulted and hit my head on the mast while windurfing with a
	   8.0 in 6.0 conditions ;-) In all, looked very do-able! That is,
	   no milling/lathe/fancy-tools-you-don't-have required!

	5) The controls also looked do-able. The consisted of no more
	   than an encoder that converted their input to the same 
	   protocol as the other end was expecting and a small display
	   that showed the status of the box'es CPU, motors, and power
	   supply. I could think the controls needed a LOT of work before I
	   could feel comfortable using them. For example, the navigation
	   controls consisted of on/off/on switches for EACH motor and
	   solenoid. So, if I wanted to steer (and I got a chance to waste
	   some battery time with his help :-) I had to manipulate some
	   12 odd switches with grace - a royal pain if you ask me! First
	   thing on my list would be to add a joystick of some sort - 
	   after all, what's the CPU for?

	6) Oh, did I forget, he also had one of those 1,000,000 candle-
	   power spotlights (a bit too focused if you ask me) to light
	   his way. It ran off the big battery and contributed to the
	   fact that he had only a few hours of fun at a time ;-) (yes,
	   it was also under on/off control but was pointed at a fixed
	   location)

	7) I better stop before the net-police send me e-mail about
	   wasting bandwidth :-)

	
	Anyways, this is an ideal project for someone who wants to have
	a LOT of cheap fun. Not only do you get to build things, design
	things, and debug things - you get to see the sea a LOT deaper
	than snorkeling (not sure if it's just me but I don't like to
	think of diving to 20 feet or more... with just a sill gas tank
	on my back... with all them sharks, cold water, and darkness...eek!)

	What am I doing in my spare time this year? Guess...

	Take care.

	P.S. Anyone have any thoughts on the above drivel? Send me 
	     e-mail with you comments/criticisims/advice.
-- 
+---------------------------------------------------------------------------+
| Filip "I'll buy a vowel" Gieszczykiewicz. | Best e-mail "fmgst+@pitt.edu" |
| All ideas are mine but they can be yours for only $0.99 so respond NOW!!! | 
| I live for my EE major, winsurfing, programming, SCA, and assorted dreams |
Newsgroups: sci.electronics