Handy use for an old monitor

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welshzadok
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Posted by welshzadok: Fri. Nov 14, 2008 - 09:50 PM
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I'm not sure if this is something other people would find useful - but there's only one way to find out...

Recently I was working on a project where I needed to have a constant graphical display of a temperature input, at fairly high speed. (It was the rate of change and general waveform I wanted to see, not just the actual temperature, hence the need for a graphical display).

I made up a bargraph display with an ATMega chip and an old monitor I had spare, using horizontal line widths scrolling up the screen, so I could see what was going on whilst testing. It was relatively easy to change the bar colours to indicate different temperature levels and status etc.

This was very useful but what I wanted then was an on screen digital readout as well, which is a lot more difficult than just horizontal lines. I had a think about it and then got a bit carried away. In the end, I worked out how to do a colour display with 70 rows of chars by up to 40 high, but I think 25 lines high would be better, 70 x 25 = 1750 chars max.

An advantage with this is that it could do vertical bars as well as just horizontal, and output all kinds of useful stuff during testing, which would be helpful on top of the normal breakpoint and trace facilities offered by the debugging tools.

The problem is that it isn't really worth the effort to make a display of this sort for just one person to use. I was wondering if other developers may find such a display useful either during testing or as a permanent display for certain types of project. With a single serial pin out of a microcontroller, providing a standard monitor output via the display board, even a modest 8 pin microcontroller could display all kinds of data. It would give a lot more scope than small LCD panels anyway.

A natural question at this point is "well, it depends on the price". I've had a think about it and probably a basic version display board with certain limitations would be from around $10 or €8 (if they were made in quantity), up to $50 (€40) for a top end version with everything.

I'd be interested to hear if anyone thinks this sounds like something useful. If so, I may take it further. I used to work for a digital scope company, so it would be nice to work on a stand-alone storage scope with VGA display if I could get this off the ground first - it would make lots of old monitors happy to be useful again!

Z.

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
Last Edited: Sat. Nov 15, 2008 - 10:49 AM
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DocJC
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Posted by DocJC: Sat. Nov 15, 2008 - 02:38 AM
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Cool

How about a photo or two of it at work?

At $10 for a base board you obviously aren't going to make a fortune on it. Are you going to post the schematic / code in the projects section?

How about some info on your user interface.

JC

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zbaird
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Posted by zbaird: Sat. Nov 15, 2008 - 05:18 AM
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I'd probably turn it into an article for Nuts & Volts, Circuit Cellar, or some such magazine. Sell the PCB and perhaps the preprogrammed AVR. You'll make a little for the article, get some (very) modest fame, and provide a useful tool to a lot of hobbyists.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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emuler
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Posted by emuler: Sat. Nov 15, 2008 - 05:41 AM
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Chuck makes a very good suggestion there. These type of gadgets are a real nightmare to sell for profit. Also, don't ever forget to factor in all the overheads, including storage/warehousing, packing/forwarding, complaints, returned merchandise, lawsuits (Americans are really good at that :P ). Also, setting up a business is not an undertaking to be taken lightly. There are tons of rules and regulations that you have to adhere to.

If you think education is expensive, try ignorance.

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welshzadok
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Posted by welshzadok: Sat. Nov 15, 2008 - 11:47 PM
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Thanks for the replies. Yes, a couple of photos showing what it can do would be a good idea. I seem to be working on a prototype anyway - regardless...
I can't really expect people to go "wow - that's useful" if there's not even anything to look at!

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BitOfAVR
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Posted by BitOfAVR: Sun. Nov 16, 2008 - 07:11 PM
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Chuck mentioned 'hobbyists' and that would be people like me, I guess. I found a lot of examples on how to put output from a microcontroller to a TV or VGA. That is fairly easy to do. Considering seveal DAC's available in most AVR's a simple oscilloscope is within reach.

But a USEFUL oscilloscope is another one.

The difficult (for me anyway) part is the input. Filtering, shielding, and autorange, are some keywords that I have come across. I haven't seen a lot of designs that focused on that part. And if commponents are used that aren't hard to come by, such a desing would be very welcome. (Top 3 of my avr wishlist)

I am also considering if using an external DAC with a higher sample rate would be useful.

'Buy a second hand oscilloscope, they are real cheap these days, you read a lot.' Good advice, but not nearly as much fun in that.

So in short, I am happy to learn from your experience.

BOA

c is for cookies

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avrcandies
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Posted by avrcandies: Wed. Nov 19, 2008 - 12:01 AM
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Quote:
Also, don't ever forget to factor in all the overheads, including storage/warehousing, packing/forwarding, complaints, returned merchandise, lawsuits (Americans are really good at that ). Also, setting up a business is not an undertaking to be taken lightly. There are tons of rules and regulations that you have to adhere to.

Too bad Steve Woz & Jobs didn't know that!

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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emuler
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Posted by emuler: Wed. Nov 19, 2008 - 12:42 AM
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Quote:

Too bad Steve Woz & Jobs didn't know that!

You can bet they did or they wouldn't have made it. :P I'm not saying don't do it; rather - do it with your eyes open.

If you think education is expensive, try ignorance.

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codesuidae
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Posted by codesuidae: Wed. Nov 19, 2008 - 12:48 AM
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I wonder if the AVGA project might be useful as a base for this sort of project.

It's really aimed more at games, but it seems like it would be pretty easy way to create a product like this, with minimal hardware.

Maybe some of the gamier features could be removed if more space was required.

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welshzadok
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Posted by welshzadok: Wed. Nov 19, 2008 - 10:43 AM
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Thanks for that link, it was a very interesting read. The title AVGA seems slightly confusing as this is a TV based project, not VGA - unless I have misunderstood it. With a TV signal (being relatively slow) and at 20 characters wide, there is enough time to create games. The difference with my design (still in prototyping) is that it displays 70 characters wide plus bar graphs etc. on a standard monitor, not TV, and is intended for serious stuff. Lo-res on a TV is ideal for Mario and Pacman - amazing what he has crammed into an ATMega168 with that project.

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Dren
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Posted by Dren: Wed. Nov 19, 2008 - 12:12 PM
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Hi,

I am working a display project at the mo (my own personal project instead of real work). It can generate a TV picture up to 768x578 pixels, or overlay it onto a PAL video signal.

I've built the HW (pretty simple stuff, a few clocks and a bit of extn memory) and I'm currently working on the SW to drive it.

The plan is that it's controlled by a 115K serial link, and have standard text and graphics drawing routines.

The entire PCB should be tiny, I am aiming at 25mmx50mm, but if that's too tight then it will be 50mmx75mm. It should be useful for all sorts of projects, oscilloscopes, sonar etc

It won't take much effort to convert it to generate NTSC or CGA/VGA, if there's the interest please let me know.

<º))))><

I am only one lab accident away from becoming a super villain.

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lynchaj
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Posted by lynchaj: Wed. Nov 19, 2008 - 12:39 PM
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Dren wrote:
Hi,

I am working a display project at the mo (my own personal project instead of real work). It can generate a TV picture up to 768x578 pixels, or overlay it onto a PAL video signal.

I've built the HW (pretty simple stuff, a few clocks and a bit of extn memory) and I'm currently working on the SW to drive it.

The plan is that it's controlled by a 115K serial link, and have standard text and graphics drawing routines.

The entire PCB should be tiny, I am aiming at 25mmx50mm, but if that's too tight then it will be 50mmx75mm. It should be useful for all sorts of projects, oscilloscopes, sonar etc

It won't take much effort to convert it to generate NTSC or CGA/VGA, if there's the interest please let me know.

Hi! Yes, there is a real need for a terminal replacement device which could use standard VGA monitor and PS/2 keyboards. The Parallax Propeller has something similar

http://www.parallax.com/tabid/25...

However, the project I am most interested in could sure use a terminal replacement board for the ECB bus. Specifically, it is a Z80 CP/M home brew computer project that uses serial IO as its primary interface. A terminal replacement board would allow it to be independent from a PC.

http://groups.google.com/group/n...

Thanks!

Andrew Lynch

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Dren
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Posted by Dren: Wed. Nov 19, 2008 - 01:53 PM
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I want to make a simple display/overlay PCB as the next project (it will include SW to act as a terminal). I already have a complete design waiting to be manufactured at the moment (that is only 25mmx50mm a user interface = 9K6 serial port, 64 inputs and 7x7segment LEDs + 8 LEDs + interrupt line).

I suppose the next stage on the display would be to make an adapter PCB that will mount it and have 1K or 2K of dual port RAM and plug into a 'standard' 28pin 0.6" socket. The CPU could then write to this area and it would be displayed as a text screen. I will think about it... one project at a time :)

I did some work on the display this lunchtime, so far it's just a nice stable display of whatever the RAM contained when powered up or I can fill it with a value. I need to port the graphics routines into it (from another project I did a few years ago). I still need to genlock the display onto an incoming video signal, which is possible but difficult SW. If I have enough I can just use a SAA1043 genlock or a LM1881 to make life easier.

If anyone has any ideas/uses/features just let me know. There's quite a bit of spare grunt left in the CPU.

These designs are extremely inexpensive, and the PCB and connectors cost way more than the electronics these days!

<º))))><

I am only one lab accident away from becoming a super villain.

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Dren
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Posted by Dren: Tue. Nov 25, 2008 - 11:51 AM
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I can now plot pixels and draw vertical or horizontal lines - impressed ? LOL

Getting it genlocked just from a /CSync input in software is a &^*) of a task, but I still think it can be done. I'm putting that off until I've finished the 'fun' graphics stuff. Going to get line thickness / rectangles going next (filled or frames), then its diagonal lines - you have to be a bit careful to chose the X or Y loop counter or you get a broken line.

I would also like to have downloadable (standard windows) fonts and scalable text, there's still enough room in SRAM (battery backed) to store about 6K, and the user can lose a screen or two if they want more (2x 768x576, 5x 768x288, 5x 384x576, or 10x 384x288) . I need to work out how to decode fonts if anyone knows a good website explaining them or has done something similar ?

Also circles are a bit of a pain, if anyone can suggest a good way of doing them ? I found that if you start on an axis and work out the maths, then the very next pixel =(Pixel1-a tiny bit) which moves it in a pixel. This creates a circle but with odd pixels on each axis, so it looks 'spikey'. If you make the radius +1 and loose the pixel 'spikes' then large circles are OK, but small ones are a bit... well like an allegro steering wheel if you know what I mean. I was thinking of doubling the res then halving it when I draw it into RAM... which is going to slow the routine down. Any ideas ?

I might use a tiny to decode the PS2 keyboard + convert it to serial as that makes life a lot easier. I believe that you have to time the pulses coming from keyboard and the MPU is accurately timing the video so it would probably mess up timing anything else at the same time.

All constructive critism, ideas, top tips, or cunning graphics routines greatly appreciated - cheers

<º))))><

I am only one lab accident away from becoming a super villain.

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barnacle
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Posted by barnacle: Tue. Nov 25, 2008 - 03:27 PM
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Regarding circles and the drawing thereof, you need to look up a chap called Bressenham. He's good for straight lines, too...

Neil Barnes
www.nailed-barnacle.co.uk

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