to project or not to project....

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dacflyer
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to project or not to project....

Post by dacflyer » Fri Mar 19, 2010 10:57 am

has anyone played with any of the smart displays such as HDSP-2531 or PDSP-1881 i belive they are both the same. or ?
Anyway i was wondering if a project like this is over my head or not, i'd like to make asort of desktop display. to type in simple small messages. any small animation like a flashing word or moving arrow etc. .
i was thinking like 4 X 16 ( 4 lines X 16 characters long. ) i am sure i could do the wiring easily enough, but i do not know if it needs any programming code or if i can just use a keyboard interface ?
anyone have any pointers or able to help me with code etc.
thanks..

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MrAl
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Re: to project or not to project....

Post by MrAl » Fri Mar 19, 2010 11:39 am

Hi there dac,


I think i can offer some insight here.

Part of the problem is cost and the other part is the interface. These two are the most important
things to consider. The third might be the display appearance itself.
If you are willing to spend a little more you can get a nice display that will interface easily but if you
dont want to spend too much you might end up with a complicated interface scheme.

The easiest displays to interface are the so called "serial" ones. They have a serial interface that is
the same as the RS232 on the computer although possibly with different voltage requirements (5v
instead of say 10v) but that makes it even nicer. The way these are done with some microcontrollers
is that two or three lines are connected between the uC and the serial display unit, and the uC
simply sends out ascii characters like 'A', 'B', etc., although in serial hex code. This isnt too much
of a problem because some uC's are made to output a serial communications the same way a comm port
does (RS232 coded) and the uC takes care of most of the work. All you have to do is set up a few
registers inside the uC via programming (during start up) and then from there you simply send the
bytes to be transmitted to the proper register in the uC and it takes care of the actual RS232 generation
and transmission, via one or two dedicated i/o pins (that often have to be initialized too, but that's
not hard to do).

The hardest ones to interface are the 'parallel' ones. These come in at least two types: the four bit and
the eight bit. The eight bit ones required a full eight i/o lines (yes, that's 8 i/o pins from the uC) and
the four bit ones require four. Obviously the four bit ones are easier to interface.
The eight bit unit uC code looks like a routine that simply sets the eight data lines to the right ascii
character and then pulses a control line or two and the display unit stores the character. With the
four bit unit the uC code looks almost the same except it sends half of the eight bits first and then
the second half of the eight bits (4 bits at a time, pulsing the control lines for each set).
The real problem with the parallel ones is that they require so many i/o lines and that means a lot
more physical wiring also.

The cost of the parallel units is much lower usually than the serial types however. The cost could
be around 5 dollars USD or less while the serial ones can be 30 dollars or more. If you are lucky
though you may find one for less.

There is a third type of display unit too though and that is the "raw" display without any controller
at all. Both the parallel type and the serial type have an onboard controller, which the raw type
does not have. That means it is by far the hardest to interface even with a uC chip. There can
be a huge number of control lines that need to be interfaced with (50 lines would not surprise me,
except that that would be a low number compared to some of them). That means a huge number
of lines have to have a connection to the uC and have to be programmed very carefully.
Because of the huge number of lines and connections required i can not recommend using these
unless you are prepared for a nightmare of programming and connections and you also happen
to have an upscale uC on hand.

Lastly, there is a trick that can be used to interface to the parallel units that involves a serial
to parallel CMOS logic chip. You basically send the data to the chip using it's data input line
and clock line (via the uC) and the output goes to the display unit. That saves on i/o lines
for the uC, but it's still quite a bit more complex than the serial display units that basically already
do that inside them.

I almost forgot to mention the display appearance itself. The display can come in various colors
and with or without a backlight, and that backlight may or may not be adjustable. You'll have
to read the spec's i guess to get an idea what you are getting.

SUMMARY...
First choice: Serial, two pins. Easy to interface, can be up and running in 10 minutes, perfect for first project.
Second choice: Four bit parallel. Takes more pins but might not be too bad.
Third choice: Eight bit parallel. Somewhat hard to interface just because there are so many i/o lines required.
Fourth (not really a choice if you ask me): Raw display with no controller. Very very difficult to interface.

See what you can find out there and maybe we can take a look and see how good they look.
Lots of electronic places on the web sell them these days. Jameco is one that comes to mind.
Be on the lookout for very very low priced units, as they may be very hard to interface with
no controller chip or 8 bit parallel.

ADDED LATER:
I read SET's reply and now i realize that i assumed that you use micro controller chips. If you dont use
these kinds of chips you probably wont enjoy using the displays as much because your applications will
be too limited. To get involved with the PIC chips doesnt take much really, and the programmers are
fairly cheap for the mid range line of products. The programming software is all free too. The chips
are nicely priced at about 1 dollar USD and up, and $2 will get you a chip you can use for quite a
few projects and is relatively easy to program. If you have programming experience in any language
you will adopt to the PIC programming quite quickly i think. If not you will have to learn about 30
instructions which isnt much really, and with those 30 you can do an awfully huge number of projects.
LEDs vs Bulbs, LEDs are winning.

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Re: to project or not to project....

Post by SETEC_Astronomy » Fri Mar 19, 2010 11:52 am

I've used similar displays in the past and they work well. The parts do require more than a keyboard interface though. Communicating with the chip is a breeze if you have microcontroller experience. The HDSP-2531 should be easier to work with than what I used as it has a built in character set. Do you use microcontrollers at all? Familiar with C? PIC or AVR?

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Re: to project or not to project....

Post by psycho » Fri Mar 19, 2010 3:47 pm

I have used LCD's more times than I care to count. Once you get the hang of it, it's cake. Also, PS2 keyboards use serial data so they are easy to use with a micro, too.

BUT, for some one with no uC experience, it may seem daunting - but there are a slew of projects out there you can learn from.

And, to take MrAl's comments a little farther, there is a cool way of doing it if your uC does not have many i/o pins available. Get yourself an I2C or SPI to parallel chip. Microchip deigned one of their dev boards like this. You can see it here:
http://www.microchip.com/stellent/idcpl ... e=en535770
If you look at the bottom of the page, you will see a pdf file which, iirc, contains the schematics. I like this method if you are running short on i/o pins. I believe there is C code samples in there, too somewhere (check the zip file from the same page).

Hope it helps,
Kevin

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Re: to project or not to project....

Post by dacflyer » Fri Mar 19, 2010 9:10 pm

ok, ist of all i need to say, i have very little.......ok, better to say no idea of programming.
so many different Uc out there it is very intimidating to me.
i go the the idea for this project from them road side D.O.T. mobile message boards.
i had the idea to make me a small desktop version. and since these displays are already yellow led in color, i thought maybe it might be a cool idea to make a desktop version.. and leave small messages for when ever....lilke when i am out, or on vacation etc..
i am not even sure if the displays when connected will show a page at a time or if they must scroll across the words across..

my vision is .....example//
page 1 =
I will be out
in the field all
day today

page 2 =
Gone to
Eastern & Grove
to change a red led
back in 30 min

just a silly example... but i think you get the idea..
if it can display page by page, that would be great.
you all have seen how the message boards are..
i figgured them displays would be perfect. and i'd just have to buld the case around the rest and conseal the rest.

i'll look for a few more opnions or suggestions before i decide what i will do.
i know the displays are not the cheapest, but i seen them on ebay at a decent price. and they are still up for the next 5 days.

NOTE >> my message does not look right after i post it. the 2 examples do not stay lined up right.. but imagine them center lined. :o)

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Re: to project or not to project....

Post by psycho » Fri Mar 19, 2010 9:39 pm

I don't know which LCD module you were looking at but you could get something like this, too:
http://cgi.ebay.com/Graphic-Matrix-LCD- ... 2ea8590563

Still pretty easy to use and you can put gfx on them, too :)
Those particular ones are 128x64 and are not color. You could spend more $ and get a color one.

If you wanted to jump in head first, you could get yourself a USB capable uC and program the messages from the USB port of your computer. The circuit would be really simple and the code should be pretty straight forward also - but I guess that is relative since I have been working with them for quite a while.

You could even use an RS232 port if you wanted to instead of USB. It is all up to your imagination and the amount of time/money you want to spend (mostly time). You never know... You may really like working with uC's.

As for what is shown on the screen, that all depends on how YOU want to do it - pretty much, if you think it up, it can be done (within reason, of course).

Hope it helps,
Kevin

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Re: to project or not to project....

Post by dacflyer » Sat Mar 20, 2010 5:38 am

psycho, i stated that the displays i wanted to use were HDSP-2531 or PDSP-1881
they are chats known as smart displays or intilligent displays..they are 5x7 X 8 displays all in a neet small package.

here is a pic of one of the displays...
http://rocky.digikey.com/WebLib/Agilent ... SPLAYS.jpg

here is one data sheet.. http://pdf1.alldatasheet.com/datasheet- ... P1881.html

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Re: to project or not to project....

Post by psycho » Sat Mar 20, 2010 9:44 am

I didn't realize that was already set in stone. sorry...

Kevin

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Re: to project or not to project....

Post by dacflyer » Sat Mar 20, 2010 4:41 pm

no problem :)
if i do go thru with the project, these displays would be perfect.they would mimick the message boards that you see on road sides used by D.O.T.

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Re: to project or not to project....

Post by MrAl » Mon Mar 22, 2010 10:15 am

Hi again,


I guess i was under the impression that you might want to build other things too once you got going.
LEDs vs Bulbs, LEDs are winning.

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dacflyer
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Re: to project or not to project....

Post by dacflyer » Mon Mar 22, 2010 10:59 am

perhaps i might, but i want to try to dabble into this 1st...

also by chance this sort of display, i have seen other types as well, ont to mention is, a single charactor led that had a onboard Uc looks like a regular 7seg. numerical led. but its actually like a 5X7.. anyone know what i am refering to..
this also might be a learning tool for me..thanks..

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Re: to project or not to project....

Post by dacflyer » Sat Mar 27, 2010 2:20 pm

ok, by the end of tomorrow i'll know what to decide on the displays i want to use..but to make things more clear, this is basically what i hope to achieve when done..but what i will have is a desk top model. and maybe it will be able to cycle thru 2,3 pages.

http://atom.smasher.org/construction

you can have a ball with this also...you can program it and or send it to someone or print it out :D

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Re: to project or not to project....

Post by dacflyer » Thu Mar 10, 2011 10:53 am

well i am back on this project, it was on th eback burner for a while., SETEC_Astronomy
was helping me this project, but he had to go out of town for a while, and i have not seen or heard from him in a long while. its like he has vanished from the group. its almost a year now. and i would like to know if someone could help me out with this again..
so far i have the electrical breadboarded, SETEC_Astronomy was working on the program, but we were having a lot of problems, either bugs or noise, i have done all i can to eleminate noise, so either it is a compatability problem or a programming problem, not 100% sure on the diagram that he sent me to use. but it is wired up as he designed..
the other problem is that the keyboard interface is good, but items appear on the wrong displays and or the backspace button ( when you want to erease ) it jumps around randomly.

if someone is interested, let me know and i can give more info..

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Re: to project or not to project....

Post by haklesup » Thu Mar 10, 2011 8:58 pm

OK I looked up both datasheets and they are parallel input devices and while I have not used this particular device, I have played with the LCD equivelent. In general, if you just want to put some stuff on the screen as a quick experiment then all you need are some debounced switches to control the 8 data lines, 3 address lines and 6 control pins. These can be run at near zero clock speed so all you need to do is setup the data pins and pulse the clock. At least this way you can get a hands on feel of what its like to be a microcontroller :grin:

As to being intimidated by microcontrollers, so am I a bit but I also recognize that price need not be an obstical. You can get a perfectly good devel kit with USB interface and all the free software you need including examples and a support website for $20. If you limit yourself to low cost USB devel kits with at least 2 8 bit ports and probably more like four 8 or 16 bit digital ports and some integrated A/D channels. Settle on one well supported chip and you're set for 1000 projects. It just takes time and will, thats the hard part.

Unless you want to key in your messages Altair 8800 style, then a uController is the only way to go. whether you load it from a USB from your PC or make a local user interface out of buttons it just makes the most sense. The effort to develop combinational logic using formal design techniques (state diagrams and such) outweighs the learning curve for a basic low level uController. Maybe writing a fancy windows GUI to communicate with your display is more than you want but recompiling new messages might not be too hard

If you were into programming then a simplest app with a text window that sends the data to a parallel port would be the least hardware implementation.

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Re: to project or not to project....

Post by dacflyer » Sun Mar 13, 2011 5:00 pm

i originally wanted the displays controlled by a micro. and the plan was to punch into into the UC with a keyboard, then hit enter and it'd be displayed on the screens. 6 total. 2 displays X3 lines
supposedly i was to press F1 to set the Uc ready for me to type the info in, and it would show up on the display, and then hit enter to save the info. and i think it was F2 to make a word flash.
and when power was cycled the info would be saved. if you hit F1. all would be erased ..
i think wiring up the displays was harder than anything. i just am clueless and cannot understand programming..(learning disability ? ) i am better with hands on, i tried to find a Uc Course at the local community collage. but they have no evening or weekend classes :(
i have the PICK-IT Programmer and the MPLab. but as i look into the lab. i am lost...the more i read into it, the more i get dumb-fused :(
the displays are bread boarded right now.. lots and lots of jumpers for parallel displays..lol

i think one thing about programming is why are there random spaces between code, and how do you ever know how many spaces to put. what happens if you miss one :O
still trying to study the language..

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