Category: Electronics

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.

Bothersome circuit

Very tired and about to go to bed, but traced and ID’d most of the parts on the old treadmill motor controller board.

It drives a motor rated for 180v DC, but my measurements say it’s putting out 330v DC which would make sense for rectified UK mains. I suspect on looking at the board that for UK use they dial the speed control trim-pot down to half so the PWM signal never goes above 50%.

Still means the motor’s running at twice the voltage it should though, which’d explain the overheating issues.

I don’t understand the circuit fully though. For one thing there’s a half-bridge rectifier essentially bridging the motor terminals. Surely that’d mean it’s perpetually shorted out? I don’t understand it, but suspect it might be something for dealing with back-EMF from the motor.

I also don’t understand how the MOSFET’s driving it. It all seems to be coming through a 5Watt resistor and some very thin traces, especially since the motor’s 2-2.5HP (1400Watt+). Maybe it’s because it’s late, maybe I’m just not seeing it and it’s just the trigger. Just can’t see it right now. But the circuit does work (even if the fuses and current breaker don’t. If something shorts it ALLWAYS knocks out the 30Amp breaker for the workshop).

It’s a single-sided PCB. Here’s my notes on it. A few figures are missing, but all components are marked.

I’m planning on making a much simpler control circuit, but it does involve a very large 220-110v transformer to get the proper 180v DC.

It’s been a good day. Castings done, experiments done, oscilloscope usable again, found artial pressure cooker for new vacuum degass chamber, some clearing up done.

DPF

Digital picture frame has arrived. Sadly does not support GIF, regular or animated. Is an odd device. Is detected as an external CD-drive, so data contents cannot be changed directly and needs to launch it’s own proprietary program to resize and upload images. (I presume this is a safety feature and means the code wouldn’t be very tolerant of wrongly sized images)
5-second fixed slideshow with random transition effects. Really only suitable for slideshows.

I suspect changing this would require cracking the case and finding a JTAG connector, followed by reprogramming the software.

So I’ve messaged the place I bought it to see if they have any different models that fit the spec to start with.

Off to the post office for now..

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]

Oyster “Clamshell” Idea

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260584878541

I shouldn’t be surprised that the cheapest RFID reader is from China. This might be something to get in the next few months. I’m interested to see if I could create an Oyster Card reader to show current balance and if you’re “touched” in or out.

I’m currently imagining something the size of one of those old credit card sized calculators. The little ones that used to run on solar. The best way would probably to package it like the card holders used on ID lanyards, where the card is slipped into the holder. To my mind this would mean the reader coil would be within a millimetre of the cards aerial, meaning it could get away with extremely low-powered use.

While it came to mind, it would probably be impractical to try and top up the reader’s batteries through induction charging when the bundle was swiped through a terminal.

That said though, there is some small encryption used on the Oyster cards. It’s supposed to take less than a second to crack on a laptop, but this tiny reader idea is not a laptop. I suspect though that the card could capture the key when the bundle is first put through a reader. That is, if the key isn’t already universal and/or the portion of data requested isn’t the bit that’s encrypted.

As a general purpose reader it would fail, but as a single-purpose device it’s at least a plausible concept.

I doubt it would get any support from TFL however, since I imagine they make quite a bit of money from people forgetting to touch out (or finding terminals are broken) and having cards charge the daily maximum fee instead.
And I feel a large number of commuters would appreciate an end to waiting half an hour for a bus only to find their card doesn’t have enough credit on it for them to get on board!

Knocked out in China, I think they’d probably sell well for a fiver. Maybe a tenner, but I feel it’d leave space for someone to undercut you then.

Anyone got any actual RFID experience to tell me if the idea’s feasible?

[20/06/2010: Amalgamating old posts from “Dreamwidth Creative Blog” into sci-fi-fox.com to re-purpose DW blog account.]