MAX7219 Propeller object. Is there one in the OBEX or in the Forums??

RobotWorkshop

I went looking through the OBEX but didn't see any objects for working with the MAX7219 chips. Is there one posted out there that I may have missed? If there isn't one in the OBEX, is there one in the Forums?

Robert

hover1

Here's on I used to get started on these cool chips. I does use the BS2 functions.

Ive' got a couple others that I'll have to dig out.



Jim

lanternfish

Try this thread

RobotWorkshop

Cool. I had some extra free pins on the Propeller and was thinking about using one of these displays:

http://www.ebay.com/itm/130524115140

If you have any other examples I'd like to see them.

Thank You,

Robert

hover1

lanternfish wrote: »

Try this thread

Yup,

Same object I posted. Different date.

hover1

The only other object I could find is one I did for a library driving 192 LED's. 3 chips in serial. It was for a tornado that would light the spinning spiral.

Nice modules on ebay! They are less than the cost of what MAX7219's used to be, ~$20.00

RobotWorkshop

I just received a couple of these modules but don't have them working yet. After taking a closer look at the datasheet for teh MAX7219 it looks like the minimum voltage for a logic high signal is 3.5V which is higher than the propeller supply. How did you connect your MAX7219 to the propeller? I'm going to try adding another chip or something in between to bring the voltage levels closer to what the MAX7219 expects.

hover1

RobotWorkshop wrote: »

I just received a couple of these modules but don't have them working yet. After taking a closer look at the datasheet for teh MAX7219 it looks like the minimum voltage for a logic high signal is 3.5V which is higher than the propeller supply. How did you connect your MAX7219 to the propeller? I'm going to try adding another chip or something in between to bring the voltage levels closer to what the MAX7219 expects.

Hi Robert,

I ran 3 MAX7219's directly from a Propeller Proto Board with no problems after two years in the field. 3.3V output from the Propeller seems to work just fine.

Just make sure you install the two capacitors close to the chip as outlined in the data sheet, and the 10K current resistor for current limiting.

I have 192 LED's running from these three chips. I wish I could find the photos showing the 384 CAT5 wires on a 4' x 8' panel for my Library installation. That was a soldering nightmare.

Jim

RobotWorkshop

If you find pictures of that soldering job that would be cool to see!

I have this working now. Maybe some of the MAX7219 chips are a bit more tolerant about the voltages on the input. I just couldn't seem to get it working reliably when connected directly to the propeller. I added a 74HC14 in between and now it works every time. I used all 6 inverters. There are three pairs back to back that buffer the signals from the propeller to the 5V device. I've done this before when I ran into issues driving multiple 74HC595's and it make those work perfect too.

I'm still going to experiment a bit to see if I can get it working without the extra 74HC14 chip. If not I'll see if I can find room on the propeller board for it or mount it directly to the back of the LED module.

Robert

hover1

RobotWorkshop wrote: »

If you find pictures of that soldering job that would be cool to see!

I have this working now. Maybe some of the MAX7219 chips are a bit more tolerant about the voltages on the input. I just couldn't seem to get it working reliably when connected directly to the propeller. I added a 74HC14 in between and now it works every time. I used all 6 inverters. There are three pairs back to back that buffer the signals from the propeller to the 5V device. I've done this before when I ran into issues driving multiple 74HC595's and it make those work perfect too.

I'm still going to experiment a bit to see if I can get it working without the extra 74HC14 chip. If not I'll see if I can find room on the propeller board for it or mount it directly to the back of the LED module.

Robert

Hey Robert,

I finally found the pictures I was looking for. They where hiding on my 1TB backup drive, and it took Google Picasa to find them.

I was mistaken about the 192 LED's. I only used 128 with two MAX7219's. The original quote was for 192, but we did not have enough room to fit them.

You can see the hap-hazard wiring that went in to this, and it still worked like a champ. Did not take any special precautions except to put the two capacitors very close to the chip as called out in the data sheet. And the current limiting resistor.

I also did two other panels with 40-50 LED's using nothing but PWM through 200 ohm resistor networks.

What a wonderful chip this is!

I wish I had frontal views of the panels in place, but the company I did this for has taken their web site down, and I was stupid enough not to take some pictures of my own. (It was 2 o'clock in the morning when I got finished)

I don't think NASA will be hiring me to do any rocket wiring, although I am very clean with my CAT5E network installs.

RobotWorkshop

That is quite a wiring job! That is a lot of soldering! Great pictures.

The example code for the 7219 helped out. I ended up extracting the code from the example and also from the BS2 object. Since I was only sending updates occasionally and didn't need the other features of the BS2 object I could avoid starting the BS2 object and wasting a cog. Never did get the display to talk reliably to the Propeller at 3.3V but adding a 74HC14 in between the MAX7219 and the Propeller fixed that. The display turned out well:

http://www.youtube.com/watch?v=WPbLiqkcx-0

It is just running a test pattern but I will have it flash other messages and patterns from time to time. Made a nice display for my back panel.

Robert