## Not a variation on 5x7 led display

6 posts / 0 new
Author
Message

This was my first project (about 6 months ago), and as such it brings nothing new to the mix. It is pretty much a beginner project, teaching you how to experiment with POV (Persistence of Vision), use of a LINE driver (transistor or darlingtons), and use of EEPROM.
It's missing a serial port, but has a keypad entry method using 5 buttons.

There are a million variations all much more minimalist than my implementation, of the same idea. The reason I chose it as a first project was because I wanted to understand a similar display's operation at work.
https://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=69118
https://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=48445

## Attachment(s):

Conrad Braam - www.softcircuitry.blogspot.com - www.plcsimulator.org
Always start off poorly, that way when you finally figure it out, you can get a few surprise hits in.

Last Edited: Mon. Mar 16, 2009 - 08:02 PM

The diagram attached to the project has a mistake (obvious once you read the code) row 6 and 7 are really PD5 and PD6 as attached above. Because the project was simply transferred from Breadboard to strip-board, its pretty much wired one pin at a time. In the diagram I only showed 1 transistor, when in fact you need 1 for each column (a total of 5). When I initially built it on breadboard, I also ended up using a driver-array chip to save breadboard space as well as my sanity - using a darlington array is the only way to go if you want to add more LED units.
To work out the pins, you need to draw the diagram in 2 ways, one for just row/column, and then with the pin mappings
ROW : AVR pin LED
PD0 = 2 to 12
PD1 = 3 to 11
PD2 = 4 to 2
PD3 = 5 to 9
PD4 = 6 to 4
PD5 = 11 to 5
PD6 = 12 to 6

COL : AVRpin : LED
PC0 = 23 to 1
PC1 = 24 to 3
PC2 = 25 to 10
PC3 = 26 to 7
PC4 = 27 to 8

edit-message push-buttons:
PORTB -
UP -x -x
DOWN -x -x
LEFT -x -x
RGHT -x -x
EXIT -x -x

Since mistakes are all part of the hobby for me (I have a very different day-job) I invite you to make a couple of mistakes yourself. I cannot guarantee you will find or use the same parts, but if you mail me some samples, I will happily test and debug them for you (LOL). As with any hobby, the cheapest and most ingenious component mix is it's own reward.
Possible column driver chip =ULN2803 or some 2n2222 transistors, if you choose to go without the column drivers, you will notice the ugly effect where letters like L with lots of leds in one column will have dim vertical strokes, and bright horizontal ones.

Conrad Braam - www.softcircuitry.blogspot.com - www.plcsimulator.org
Always start off poorly, that way when you finally figure it out, you can get a few surprise hits in.

And what's there preventing the transistor or the led matrix or the AVR from exploding? :?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

Aaah, glad someone asked, runs off tiny batteries. Practically I am not a guru at driving LEDs, I go more by getting the drop voltage than by working out the current; so I am not showing 1KOhm transistor bias current limiters, alternatively if using a darlington array, I used 100 Ohm dropper on each collumn.

A big detail missing from my hand-drawn scrawl :oops: I wanted it to not use much power at all, which my finnished unit does, using just 3 small watch-batteries ...the project actually runs at 4 to 4.5 volts, more than enough to pop the LEDs one at a time. But I found the a value for droppers more by experimentation which did not cause the leds to burn too brightly, while if you run this off a regular 5v rail, it is no longer portable.
Thanks once again for the warning!!!

I would love to get an oscilloscope and get a proper average power consumption per LED worked out. Another problem I did not manage to overcome is the ghosting, even after giving the I/O lines longer to settle, I cannot figure out why you still get ghosting (another reason a 'scope would help). Any Ideas?

Conrad Braam - www.softcircuitry.blogspot.com - www.plcsimulator.org
Always start off poorly, that way when you finally figure it out, you can get a few surprise hits in.

Quote:
Any Ideas?
It has been discussed before, may want to do a bit of searching on this forum.
Basically you turn OFF the leds before changing the data. I have a few led boards on my website. :)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

I also checked out John's site http://www.members.optusnet.com.au/ampertronics/signs.htm specifically should provide some inspiration, if not a source for a finished product that already does what you want.

Conrad Braam - www.softcircuitry.blogspot.com - www.plcsimulator.org
Always start off poorly, that way when you finally figure it out, you can get a few surprise hits in.