Tag: electronics

NTSC / PAL Field Counter Test Fixture

Due to corporate confidentiality, I’m not allowed to show much of what I’ve worked on.  The Field Counter is one of the exceptions to this rule since it was never designed for sale.

This simple Microchip PIC based test fixture was used to insert a time stamp on every field of an NTSC / PAL video signal.  Since video signal frames consist of even and odd fields, it would be convenient to label each field with a unique identifier.

In my original code I concentrated on the NTSC signal.  I determined the field output by sending the FIELD pulse from the 1881 synch separator to the Microchip PIC.  This gave me an even/odd field determination.  With a 20 Mhz clock giving me 5 million PIC program cycles per second, I had a very comfortable margin of program cycles to play around with.

The processor would determine the next number in the sequential time stamp, and would send that to the NEC uPD6450 character display chip.  When the next field was displayed the character display would include the time stamp as the overlay.

The software would then “count up” to 99 hours, 59 minutes, 59 seconds, and then roll over.  I figured that 4 days of continuous testing would be overkill, and didn’t code the ability to count any higher.

The original field counter saw quite a lot of use.  It was used to figure out when our equipment was digitizing video out of order, getting fields or frames “confused” and exactly how.

It was also used to test the promises of products sold by original equipment manufacturing companies who wanted our company to resell their products.  This is how we learned that one company was only digitizing the odd fields of incoming video, or how another company averaged the odd / even fields together in a very lossy manner.

This tool was so useful that I built version 2.0.  This is the hardware I’m showing here.  This newer version included a serial EEPROM and an RS-232 transceiver, giving it the ability to communicate to a PC using Hyperterminal and add text to the video screen to indicate the test being performed.

I also included menu navigation buttons, and some hardware hooks to allow this tester to “watch” an SVGA signal and send a trigger output on any given SVGA scan line.  The buttons were very useful, but when I determined that video was moving away from SVGA I never bothered to implement that function.

The field counter became very useful in other ways.  I would hand these devices to our interns and have them modified for various purposes. There was even a prototyping area on the circuit board that allowed for easy modifications.

One modification by a very bright intern allowed the device to control the PAN/TILT/ZOOM functions of a camera by the use of a standard television remote controller.  This was a proof of concept idea, that a cheap controller could be used to control a security system.  Unfortunately Marketing didn’t approve.

Another modification allowed the platform to monitor a thermocouple while controlling the heat in a standard $30 toaster oven.  This would allow the toaster oven to be used as an electronics reflow oven.  I have used this oven to successfully reflow a couple of boards that I’ve made.

Unfortunately, since this was simply test equipment I’ve never been good about source control for the firmware.  Over the years several interns have hacked up the source code, and I no longer have my original.  You can see that in the code here.

I still have one of these units to play with.  I may re-write the code in C++ and upgrade my reflow oven.   But there’s a lot of other things on my plate these days, and this is not a high priority.

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