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Electronic Message Display

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johnc

New Member
Hi there,

I am looking at a project for a group of students that involves building an Electronic Message Display. This is something which needs to be completed over a six month period ( approx 6 hours per week) and has to be reasonably substantial. Although the abilities of the students are limited, I do have a solid background in electronics.

The basic idea is to design a LED message display based upon building a sizeable LED matrix which will display 1 or 2 lines of text. Whilst there is little hardship in soldering hundreds of LEDs onto a large PCB or PCBs, it is really a question of how to drive the display?

Ideally it would be useful to use a PC to input any required message, and for this message then to be displayed on the LED display, perhaps scrolling sideways.

I have trawled the net and the closest I have come is at www.bobblick.com/techref/projects/ledsign/ledsign.html

Sadly this display is not large enough and so has limited use for me although some adapting could be done.

Each student will work on a different part of the project and will have to produce a reasonable report on their efforts.

If anybody knows of any sites that may fit the above then I would be very grateful for a pointer. If anybody has any ideas, that too would be very helpful.

Many thanks for taking time to read this.

Regards

John
 

mechie

New Member
Possible design oppertunity

John your email address does'nt work :oops:

I have been thinking about your project and wondered if you fancied a crack at designing something as the circuit you linked to seems a bit sad. If you are interested then I feel such a display could be constructed (possibly on a modular, tile based display concept - allowing extension as time allows?).

I was playing with an idea of an 8 by 64 LED matrix (possibly as 8*16 LED
tiles - capable of 2 characters) which would be convenient for an 8 bit data
bus but conventional refresh techniques (multiplexing power to each column for 1/64th of the available time) would mean current pulses of 64*10mA = 640mA to simulate a steady current of 10mA? too high for LEDs to survive? so I started to consider adapting TFT technology and having a latch per LED column (maybe UCN5801) so that the (some form of) controller could send the bit-map to be displayed and just let the 'latching' display tile get on with it (modular!).
 

samuel esu

New Member
electronic display board

Hi,:D
I'm looking for a circuit on an electronic display board that can be programmed to display words/sentences -scrolling sideways.
Can any one help me :?: you can also mail me:[email protected]
Ill be very grateful.thanx.
 

herbymcduff

New Member
Heathkit comes with alot of variety of circuits you can build. They will even supply the parts. And I'm pretty sure you can find your message board in there web site.

http://www.heathkit.com
 

Vernon

New Member
The Australian based magazine Silicon Chip, published 2 such projects in the past. If I'm not mistaken one of the projects could be found on the April 97 issue of Silicon Chip. Check out this website for further details, http://www.siliconchip.com.au
 

Re

New Member
My company has asked me design a 24 or 26 by 2 line display which I was going to use 7x5 dot matrix units because I have many of them.
It may seem a bit complex but I think I may just use 52 D type flip flop 74HC273 (data sheet attached) in two buses and refreshing each latch every 1mS or so. The idea would be to use a pic chip with a serial interface RS232. The unit would be about 700mm long and would need a beefy power supply.

Best Regards
 

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Re

New Member
Me again

I should have mentioned that there are chips that can control 4, 5x7 dot matrix from Maxim (max6952eax).
 

kinjalgp

Active Member
Instead of using 52 Latches, don't you think it would be easier to use multiplexing technique. This will reduce the circuit size to a considerable amount. You'll probably end up using 10-15 ICs maximum.

The dedicated display drivers ICs from Maxim are difficult to procure and are also costly. Plus they have their own ASCII character set so you can't display custom characters using it.
 

Re

New Member
Multiplexing is a must, you need to update each column for each 7x5 matrix unit. All of the 7x5 matrix unit can be on the same bus but you could not turn on each column long enough to get a decent intensity. At most I would thing 6 or 7 columns per latch, and there are 240 columns in a 2 by 24 segment display. I have not had much success in getting a high intensity from scanning LED display with more than 5 separate segments to scan, so I have always used latches. Please tell me what I am doing that you would not?
 

kinjalgp

Active Member
When multiplexing LEDs, the series resistor used is much smaller than used with constant DC supply. This pulses the LEDs with more than 4 times the rated current so as to maintain same level of intensity. And yes LEDs do take that much current pulses without frying themselves. :)

But if you are falling short of multiplexing time, then use of latches is suggested as this problem occurs in very long displays.
 
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