Getting a frame pulse early !

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Postby Steve Anderson » Thu Nov 29, 2012 6:00 pm

Yes, same here too. I don't submit anything until I'm happy that it works as advertised and is reproducible by the majority of members. One of the stumbling blocks these days is the use of programmed devices, AVRs/PICs etc. Few have the facilities to program them and for most the cost of a programmer isn't worth it. So it's up to the likes of myself to make pre-programmed chips available either via the Club Shop or directly to the user.

You can build your own programmer, I did at first, but I found that you almost have to build one for every different flavour of micro you might use. In addition most of the DIY programmers use the parallel port (LPT) on a PC which is rapidly vanishing from most recent machines. You can get USB to LPT port 'cables' (serial RS232 also) from the likes of FTDI in Scotland for around 16-20 quid. I would guess Maplin too.

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Postby AncientBrit » Thu Nov 29, 2012 6:28 pm

re USB to Parallel port converters.

I purchased one from Maplin.

Afraid to say it didn't work in my application where I wanted true bi-directional comms to pass 8bit video to a PC together with handshaking.

Not tried the FTDI one, probably would be okay.

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Postby gary » Thu Nov 29, 2012 7:34 pm

It's a funny thing with USB to Parallel Port converters in that they never do seem to work as advertised and as it's implementation is mainly a firmware thing it is hard to understand why.

I notice a lot of people are using micros to programme micros these days - almost like a bootstrap thing.
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Postby Steve Anderson » Thu Nov 29, 2012 8:18 pm

I do have a couple of multi-port USB to RS232 'dongles' which are truly bi-directional and fully duplex, transmit and receive at the same time. They're not made by FTDI but do use the FTDI chips internally. All you have to do is download the VCP driver(s) from the FTDI site and off you go. But I haven't tried any parallel-port versions. They do go to speeds far in excess of what is usually thought of in a serial port....keeping leads short, it is still RS232 after all.

Anyway, off-topic as usual...my fault!

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Postby Viewmaster » Fri Nov 30, 2012 12:55 am

Steve Anderson wrote:Anyway, off-topic as usual...my fault!

Steve A.


Well this topic is near exhausted anyway, Steve.
Just been fascinated this morning watching that inserted 32 line pulse moving between line 31 and line 1 as I twiggled the timing pot.

Also twiggling that 2 meg pot to elongate the frame pulse a full frame, you will recall.

So back now to the construction of the Antique frame etc to hold everything.
And a start soon on those 3,000 odd LED joints.

The final pot twigging will be best done on a test card picture methinks, that is, if I ever get to see one.
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Postby M3DVQ » Fri Nov 30, 2012 2:19 am

This is why I like using AVRs :) I can add in circuit programming for the cost of an npn transistor and a few resistors if I don't mind losing a couple of GPIO pins (or at least having constraints on what I connect them to).
It still requires a serial port of course, but since I always have a usb-serial adapter handy it's not worth building an FTDI chip into the design when it's only for me :)
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Postby M3DVQ » Fri Nov 30, 2012 2:33 am

re. usb parallel port adapters. They are only designed to be LPT ports and aren't intended to be (ab)used for general purpose IO. Unless it specifies otherwise I would always assume the lowest common denominator in hardware like that. I seem to recall that there are even adapters which enumerate themselves as a generic USB printer!

The same is true for usb-serial ports in that at least one of the chips commonly used doesn't allow you to "bit bang" the handshaking lines - it is simply a serial port. Unfortunately it's pretty well impossible to know what you're getting with most of these things as even name brand adapters use whatever board is coming out of china cheapest this week. Luckily it seems that adapters based on the "Prolific" chips are most common and in my experience they all seem to be able to bit bang individual pins. YMMV of course!

Course if you're designing a product you should just buy an appropriate FTDI chip and put a USB socket on your box. That way you don't have to troubleshoot users' usb to serial adapters for them :)
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