Need suggestion for chip

[RonH]

I'm making an LED message board with 8x8 LED matrix (8 of them), using one 8bit port for the cathode on the anode side I'd like to be able to pulse a pin and have a counter increment up to 64 then reset, in this way I'll only use 1 pin and get my desired effect, the 4017B looks good but I don't think I can gang them together on the other hand I thought about using 74HC244 and toggle the enables on and off for each IC (8 of them), this would use another 8 bit port and either another 8 bit port for enables or 4 pins and another chip to decode BCD.

Does anyone have any elegant ideas?

btw I'm using a PIC16F877 (3 8-bit ports 1 5-bit port and 1 3-bit port)

If I can move to a smaller part after the prototype is made I'd like to do this also having the USART available would be helpful (on one of the 8-bit ports).

Ron

 

[weegee]

i dont know how to do what you want with the bits you have specified, but the max7219 will handle 64 leds, and only use 3 pins on your pic, and they can be cascaded, without using any additional pins. it will also do brigness ect. the datasheet can be found on the maxim-ic website.

 

[Papabravo]

Check out the MAX6954. It is an awesome part. I recommend running the LEDs at 3.3 to 3.6 Volts as opposed to 5VDC. Crunch the numbers and you'll see why.

 

[jumides]

I'm making an LED message board with 8x8 LED matrix (8 of them), using one 8bit port for the cathode on the anode side I'd like to be able to pulse a pin and have a counter increment up to 64 then reset

Is this what you ? 8 x 8 = 64 pcs of led ?
you need 74138 (3 bit to 8 bit decoder)

**broken link removed**

 

[RonH]

I'm making a message board from a matrix of 8x8 LEDs (They are in 8x8 blocks). I'm not using 7 segment.

I have the code written for 1 matrix block and now I want to expand this to up to 8 blocks in total. the Max devices are made for 7 segment LED's. basically I want to address the Column of each matrix and write to the row to light up to 8 leds at a time and then advance to the next column and write to the row again.

I have made up a waveform of what I'd like to achieve, but this is not set in stone.

Ron

 

[kchriste]

the Max devices are made for 7 segment LED's.

Don't forget that so called "7 segment LED's" are actually arrays of 8 LEDs. (Lets not forget the dp)
A quote from **broken link removed**

Drives Up to 16 Digits 7-Segment, 8 Digits 14-Segment, 8 Digits 16-Segment, 128 Discrete LEDs, or a Combination of Digit Types

If you really want to use older chips, you could use shift registers such as the 74HC164 etc...

 

[weegee]

i think the 7 segment trap is the one thats most people fall into when looking at the max chips. I use these regularly, to drive a couple of hundred leds, some leds are 7seg, some are bar graphs, others are backlights, some out on there own as problem indicator lights. They are mix and match, yet happlily coexist being driven off of a few Max7219.

As a few of the posters have said, there are alternatives, and the newer ones are better. I used this the MAX7219 in my first BIG led project, so i have got used to it, know its quirks, and have oodles of code for it and a box full of them. If your new to these chips, id suggest you start with one of the later maxim led drivers, as they are even more capable, and can handle way more leds (although im sure they are wired in a different configuration from the older ones ?)

 

[Papabravo]

The MAX chips allow you to bypass the 7-segment decoder and control each "segment" with an individual bit. The duty cycle control, constant current source, and the Charlieplexing algorithm make them really hard to ignore in favor of a discrete solution.

 

[Brian Hoskins]

I have the code written for 1 matrix block and now I want to expand this to up to 8 blocks in total.
Ron

Can I ask Ron, what language are you developing this in?

Brian

 

[Papabravo]

I'm with Ciarcia; solder is my favorite programming language too!

 

[RonH]

I am an assembly guy normally but I thought I'd give C a try on this project.

I had a look at the Max chip, they actually look pretty good except for the price, Digikey sells them for $11.43 each total around $90, I can make it work with a 4017 and a few 74HC244's for under $5.

So I came up with this solution a 4017 (or maybe a 4022 might be better) clock and reset and 8 74HC244's with each one requiring an enable which can be run off a 1 to 8 decoder.

Ron