PIC 405 line pattern generator

[Amrad]

Hello Terry

Here's the history: in the beginning, transmissions were asynchronous, i.e: mains locked.

That is not asynchronous, that is synchronous! To be asynchronous, there would have to be no mains lock.

Regards,

Dave.

[Terrykc]

Oops! Obviously got it wrong way round! 

[FRANK.C]

Hi Terry
Thanks for the explanation and history, it shines a lot of light on everything.
it's interesting to know how things have developed and why.

Frank

[Mkstevo]

As somebody who has battled with programming PICs for many an hour, I think you should be congratulated on your work. It really is marvellous to see, I'm very impressed. Well done.

[FRANK.C]

Hi mkstevo
Thanks for your comments. I enjoy playing with PIC's but as you say it can be a battle sometimes. I have spent many hours trying to find out why something which seamed totally irrational was happening, inevitably it always turns out to be a school boy error that I have made, but It's all part of the fun.

I should soon have the software done with shorter lines.
I had intended to reduce the total line length to 98.83 uS but this turned out to be a non runner.
Reducing the length from 99 uS to 98.83 uS would be done by shortening each line by one instruction cycle, which isn't a problem for the lines however in ordered to keep the timings correct each broad pulse in the field sync needs to be reduced by half that amount which cant be done.

Instead I will reduce each line by two instruction cycles to 98.66 uS. The broad pulses can then be reduced by one instruction cycle.


Frank

[FRANK.C]

I have the new software finished, it can be found at that same link and I have also built a more compact version that uses phono sockets in place of BNC.

pictures below.

Frank

[Cathovisor]

That is... astonishingly small, Frank! Amazing...

As soon as I've got this Dynatron chassis off the bench, I'll do the long-awaited test report on the generator. Which will also force me into getting my Sony CVM9-90 working!

[ntscuser]

I have the new software finished, it can be found at that same link and I have also built a more compact version that uses phono sockets in place of BNC.

Very smart and very elegant!

[FRANK.C]

Thanks chaps.

The next thing that I will build to go with it, is a System A modulator that will cover all 13 Channels. It's a design that I fond over on UKRRRDF by David Robinson.
When the time comes I will start a new thread for that.

Frank

[Cathovisor]

Thanks chaps.

The next thing that I will build to go with it, is a System A modulator that will cover all 13 Channels. It's a design that I fond over on UKRRRDF by David Robinson.
When the time comes I will start a new thread for that.

Frank

That sounds like a truly excellent addition to the arsenal, Frank. I've looked at the design and it uses the same modulator IC as the Aurora standards converter.

I'd better get the spectrum analysers sorted out (TBH the Marconi works, but is limited to 400MHz: the HP goes to 1.5GHz but is faulty).

[FRANK.C]

Hi Cathovisor
That's the one, It uses two MC44BS373CA modulator chips that are getting difficult to find. I bought my lot on ebay about a year ago, there were several suppliers listed back then. I took a look today and cant find any however there are still some listed on Aliexpress.

Being able to switch between channels is a great advantage particularly when you have both London and Birmingham TV's.
I have it practically finished and it appears to preform well.


Frank

[Michael Watterson]

A pair of readily available NE612 / SA612 will work, though only to lowest Band III channel.
Cheap DIL on ebay.
The trick to get AM is to pull down ONE only of the balanced input pins. Try 22k I think. Or 47k variable in series with 2k2. Decouple the pin for LF video or audio. Use series capacitor on other input pin to video / audio.

The Oscillator is simple to use with ceramic, crystal or LC. A varicap can be added for FM (525, or 625 or other) or DC fine tuning. Phase modulation can be done by adding a proportion of LO out to the Mixer out.

Works fine for LW /MW audio modulator too. Without unbalancing the input (or adding in the Osc Out) it's a Double Side band Suppressed carrier mixer and Local oscillator.

[FRANK.C]

Hi Michael
That's an interesting little chip that I have not come across before, it's good to know there are alternative ways.

Before I settled on the MC44BS373CA I was thinking of using a pair of MC1946 and two AD5891 DDS modules as there oscillators. It should have been able to do all the Band 1 Channels which is all I need really.

Frank