7x5 LED Moving Display - Nuts Volts March 07

T&E Engineer

I was very happy to see Jon Williams code and program on building and programming the SX-28 in SX/B for the LIFE game in this months Nuts and Volts magazine. I immediately built it but what I liked better was his routine for the LED moving display "SX-LIFE" followed by an exploding frame animation and then a "?". I was able to easily modify it for a 7x5 35 LED module I have from Jameco - LTP747 part. I have attached the datasheet. I adjusted the coding so that the letters are 7 LEDs across by 5 LEDs high. I have attached my code which was a modification of Jon's original.

My wife·has recently·started to make her own bead jewelry. I thought it would be great to make some sort of a moving display pendent or charm like device on the end of a necklace and see if it would work and still not look too big. I know that the SX-28 in SMT form is smaller than the LTP747 so that would be good and SMT resistors could be added leaving only one issue of powering it. As you can see I corrected the brownout value in the code for 2.6v to run off of a 3 volt supply. It does run off of 2 AA batteries good. However, using a 3 volt watch battery doesn't supply enough current to really even turn on.

Is this possible to use any lithiem or high current small watch battery (smaller the better)? Has anyone ever done this before?

Comments or suggestions would be appreciated - to mainly see if this is feasible. It reminded me of the Parallax RobOlympic badges which perhaps I should re look at again for power requirements.

You can go to www.nutsvolts.com to get the article schematic of the original 8x8 design too.

Forrest

Thanks for the modification. I bought some of those 7x5 LED display's from Jameco awhile ago but haven't gotten around to using them.

I was surprised at the simplicity of the original circuit, using just (8) 470 ohm resistors to drive 64 discrete LED's with a SX28. Most designs, including the RobOlympic medals use transistors to keep power requirements down.

Here's a portable Pong game that uses (4) 7x5 LED displays - I bet it could be modified to run on a SX28 processor
www.chilli.net.au/~amarch/upong/upong1.html

JonnyMac

I do try to keep things simple. As it turned out, the LEDs I got from Mouser were tremendously bright so I've had no troubles with the 470s which limits the RC port current to a safe setting when multiplexing is used as in that project. If you want to be really safe you can put in 680s or 1Ks. I ran that thing on my desk for over a month and as part of a costume (those of us in the Halloween industry get a head start on parties with trade show gatherings) and never had a lick of trouble. I sent my prototype to Ken Gracey to play with so he can confirm for you that it works well.

Post Edited (JonnyMac) : 3/6/2007 1:09:46 AM GMT

T&E Engineer

I'm using 5 100 ohm which seems to be ok. The LTP747 is not overly bright to begin with and 470 ohm is a bit dimmer so 100 is ok for me with no problems.

Thanks for the feedback. All positive comments are welcome!

Ken Gracey

Indeed, it works well! Nice job on the PCB design, Jon.

Ken Gracey

T&E Engineer

Now JonnyMac's post makes more sense to me - AKA Jon Williams.



Great Job JonnyMac!



I am working on 7x5·characters for the scrolling LED message now.

T&E Engineer

I have made some progress with the program. The data message can now scroll left, right, up or down now. I also used a routine from the RobOlympics SX/B code that allows you to enter in your data message in a data statement for simplicity and it scrolls it. However, at the moment it only allows 8x8 or 7x5 (either one) LED matrix setup. This column setting uses 8 outputs (RC) to scroll.

Col_Mask:
· DATA %11111110
· DATA %11111101
· DATA %11111011
· DATA %11110111
· DATA %11101111
· DATA %11011111
· DATA %10111111
· DATA %01111111

Using variations of this I can scroll in different directions (along with changing some code in the Interupt routine).

However, If I want to use a column longer than 8 LEDs, external chips would have to be used as Jon stated such as the 74154 or 74138. My circuit uses anodes for the column LEDs so these chips produce negative outputs and would have to be used with inverters.

Can anyone tell me any other chips to accomplish this using all 8 RC outputs (or can I use less like 4 or 5) into something like a 74154 or 74138. If the RA lines are used instead then only 16 outputs are possible·and I would like to get 20 outputs for my LED matrix I am now using. I have a 20 x 7 LED matrix being 7 cathodes high by 20 anodes wide. I have both 74138 and 74154 and inverter chips too to test this with - but would like to keep the external chips to a minimum.

I also tried using a 4017 decade counter with the clock line going into RA.0. I used HIGH RA.0 and LOW RA.0 statements inside of the interupt routine. However, the timing wasn't right and it displayed as a mess of LED's going all on and off depending on the data being brought into RB.

Any ideas or suggestions would be appreciated. I'm close I know it but need some design chip considerations.

Thanks.

JonnyMac

You could always port the program to the SX48; that would give you lots of pins on one chip and the SX/B array size in the SX48 is not limited to 16.

T&E Engineer

I like that approach alot! I ordered·(2) SX-48 boards from Parallax BUT they were on backorder until the end of the month.

However, in the mean time I would still like an SX-28 (Professional Development Board) approach using external parts (to a minimum) to see how this might be done.

Thanks for the great suggestion!


Post Edited (T&E Engineer) : 3/8/2007 6:34:31 PM GMT

Capt. Quirk

Not the SX 52 boards though, If U want a board sooner

T&E Engineer

I called Parallax and they said this is an End of Life (SX-52 protoboard) but they have some available at the same $9.95 cost. I changed my order and they will go out today for the·(2) SX-52·Proto boards.

It was good that you told me about this since the SX-52 has more capability BUT this makes sense why it was not listed on the website (end of life).