Thanks Tom, I'm assuming by stiff you are referring to R, 10k from CS to +5V near the first array in the chain? I'm going to break the Clock and Chip Select lines after the first five arrays, and run the last five through the LLC on the other two channels, first I will try the pullup, maybe that's the whole problem.
I have been re-reading this thread from the beginning, which I recommend to anyone planning to use these arrays, lots of good onfo. Without the code examples, I wouldn't know where to begin. Duane posted that a single board can draw as much as 700ma, I thought that was a lot, then I thought again, there are 64 LED's. My first hardware build will be an appropriate power supply.
After this project, I want to get a hold of one of the 64x64, 16 board set-up's and use your PASM driver, that looks like it would be really fun to play with.
Looking through my document archive, I found this Parallax AppKit on the MAX7219. You guys probably already know about it.
The figure also shows pulldown resistors on inputs to the MAX7219. When power is first applied to PIC or Stamp controllers,
or when they are reset, their I/O lines float. The MAX7219 can see this as valid data and display garbage until the PIC or
Stamp gains control. The most common result is that the MAX7219 enters test mode with all segments lit at full brightness.
This can drag down the output of a marginal power supply preventing the PIC or Stamp from ever getting properly
powered up. The pulldown resistors prevent these problems. If you want to reduce the parts count in a design, try
eliminating the pulldowns on the clock and load lines, but leave one on the data line. The rationale is that although the
MAX7219 may still clock in bad data, it will not enter the test mode, which consists of all 1s.
Current thinking is that a pull-up on chip select is the best way to avoid lamp test. That said, a pull down on data, and clock for that matter, won't hurt and may help with stubborn cases (like long power supply rise time).
I agree with Tom. As long as the chip select line is pulled high, the MAX7219 chip should ignore the data and clock lines.
Having the test mode active can be a real pain. It can end up causing the Propeller to reset which in turn limits the ability to turn the test mode off (since the Prop doesn't have time to turn off the test mode).
I couldn't find a schematic related to this board, so I came up with something on my own, I would like to submit it for your approval. Maybe it will help someone else.
I use these sorts of displays in a lot of projects.
What do you mean by expensive?
It's been a couple years since I've purchased bare MAX7219 chips but when I did they cost about fifty cents (USD) each. I'm not positive I received genuine chips but the chips I purchased worked.
Do you have recommendation for a microcontroller replacement? Some sort of AVR chip?
Of course once one has an appropriate microcontroller chip there's still a small matter of programming to take care of.
@MikeDYur I don't see anything wrong with your schematic.
The MAX7219 is >$6 in 100 quantities. Micros are <$1 that could do the job hands down.
From what I see, most of the features are not being used, just the clocked serial in/out.
The MAX7219 is >$6 in 100 quantities. Micros are <$1 that could do the job hands down.
From what I see, most of the features are not being used, just the clocked serial in/out.
I must have purchased fake chip. I paid about $25 for 50 chip.
As I mentioned the chip I purchased appear to work fine.
If real MAX7219 chips are $6 each then I'm guessing the $2 LED displays on ebay are using fake chips.
If real MAX7219 chips are $6 each then I'm guessing the $2 LED displays on ebay are using fake chips.
I bought ten of the unassembled boards, the parts quality looked excellent, the chips all looked identical, markings, case , pins, looked like something strait out of a major semiconductors factory, I guess the only way to tell is by performance, if it dosn't meet datasheet specs, its not the real deal. I don't mind using sub-standard parts, as long as they work for my intention's I'm not making anything for resale or critical applications, so if I can buy a good deal to tinker with, its better than not tinkering at all.
The MAX7219 is >$6 in 100 quantities. Micros are <$1 that could do the job hands down.
From what I see, most of the features are not being used, just the clocked serial in/out.
Jameco wants $5.25 in 100 quantities. I don't have an account at Maxim, so I can't quote them but I gotta believe it is a little less. But not enough less to enable ChinaInc to package it with 64 LEDs and a PCB for $1.50. I pretty much have to believe they are counterfeit chips.
One nice feature of the 7219 is constant-current segment drivers. Don't need no steenking resistors.
20 pins is just enough: Eight anode pins, eight cathode pins, three SPI, and one data out for daisy-chaining.
Alcohol should not wipe off a factory laser etching.
Yes, I had to use a jewellers loupe to see to see what I was talking about, I have had chips that alcohol did effect, a long time ago though. A chip isn't much good out of circuit and with no markings, laser etching is a wonderful thing, like branding cattle in the old west.
A micro won't replace the MAX chip simply because it doesn't have the I/O and total current handling capacity. Even if each LED were only driven at 5ma average but 40ma peak for a 1/8 duty to each LED then that would still be 40ma continuous times 8 sink plus 8 source lines = 320ma but in terms of heating it's practically double due to source and sink on the same substrate. But that is not even full brightness. Fake or not, the MAX chip does the job although it has a crummy way of cascading chips.
There are a lot of posts out there about how to spot the fake MAX 7219 chips. Google for "max7219 fake" for a lot of info.
Yes, there is a lot info on these chips, people have been wondering the difference for a while. Break the chip open to find out, or the package looks like a dead giveaway.
By the way, to get back on topic...I'll be interested to see the solution for getting the 8x8 matrix boards working. I tried using the drivers months ago and couldn't get them going properly.
By the way, to get back on topic...I'll be interested to see the solution for getting the 8x8 matrix boards working. I tried using the drivers months ago and couldn't get them going properly.
I've written drivers for cascadable MAX7219s before so what was your problem?
It's been long enough that I don't remember what exactly the issue was, just that the drivers I found I struggled with. The only driver in OBEX is not for 8x8 modules but for 7-segment display.
The only driver in OBEX is not for 8x8 modules but for 7-segment display.
Based on what Mike said, it sounds like the code attached to the third post of this thread is working reasonably well. The name of the attached archive is "Max7219Demo140116e - Archive [Date 2014.01.16 Time 22.19].zip"
Which 8x8 arrays are you using? I think the above mentioned code is what I used when making the video embedded in this post. The arrays in the video where inexpensive ones sold by ICStation.
Comments
Yes, I think that should work.
EDIT: I fogot to mention that the pause in the middle of the video is me reloading the software.
I have been re-reading this thread from the beginning, which I recommend to anyone planning to use these arrays, lots of good onfo. Without the code examples, I wouldn't know where to begin. Duane posted that a single board can draw as much as 700ma, I thought that was a lot, then I thought again, there are 64 LED's. My first hardware build will be an appropriate power supply.
After this project, I want to get a hold of one of the 64x64, 16 board set-up's and use your PASM driver, that looks like it would be really fun to play with.
Having the test mode active can be a real pain. It can end up causing the Propeller to reset which in turn limits the ability to turn the test mode off (since the Prop doesn't have time to turn off the test mode).
Mike
EDIT: Thanks kwinn for the sugestions.
A cheap micro with 20 I/O should do the job easily.
I think the main appeal in this case is the inexpensive LED arrays which include a MAX7219 chip.
Besides these 8x8 arrays, MAX7219 chips are also used on 8 digit 7-segment displays.
I use these sorts of displays in a lot of projects.
What do you mean by expensive?
It's been a couple years since I've purchased bare MAX7219 chips but when I did they cost about fifty cents (USD) each. I'm not positive I received genuine chips but the chips I purchased worked.
Do you have recommendation for a microcontroller replacement? Some sort of AVR chip?
Of course once one has an appropriate microcontroller chip there's still a small matter of programming to take care of.
@MikeDYur I don't see anything wrong with your schematic.
Probably but I don't program anything but the BS1, BS2 and Propeller, so I am stuck in that respect.
Mike
From what I see, most of the features are not being used, just the clocked serial in/out.
I must have purchased fake chip. I paid about $25 for 50 chip.
As I mentioned the chip I purchased appear to work fine.
If real MAX7219 chips are $6 each then I'm guessing the $2 LED displays on ebay are using fake chips.
I bought ten of the unassembled boards, the parts quality looked excellent, the chips all looked identical, markings, case , pins, looked like something strait out of a major semiconductors factory, I guess the only way to tell is by performance, if it dosn't meet datasheet specs, its not the real deal. I don't mind using sub-standard parts, as long as they work for my intention's I'm not making anything for resale or critical applications, so if I can buy a good deal to tinker with, its better than not tinkering at all.
Jameco wants $5.25 in 100 quantities. I don't have an account at Maxim, so I can't quote them but I gotta believe it is a little less. But not enough less to enable ChinaInc to package it with 64 LEDs and a PCB for $1.50. I pretty much have to believe they are counterfeit chips.
One nice feature of the 7219 is constant-current segment drivers. Don't need no steenking resistors.
20 pins is just enough: Eight anode pins, eight cathode pins, three SPI, and one data out for daisy-chaining.
The real ones are pricey:
http://www.mouser.com/ProductDetail/Maxim-Integrated/MAX7219CNG+/?qs=sGAEpiMZZMsPdFgpQMKDR/Oo0Y%2b3/mKR9vg7XKixKMo=
https://www.adafruit.com/product/453
http://www.digikey.com/product-detail/en/maxim-integrated/MAX7219CNG-/MAX7219CNG--ND/948191
Are they not laser etched?
Alcohol should not wipe off a factory laser etching.
Yes, I had to use a jewellers loupe to see to see what I was talking about, I have had chips that alcohol did effect, a long time ago though. A chip isn't much good out of circuit and with no markings, laser etching is a wonderful thing, like branding cattle in the old west.
Your evaluation of current handling capabilities summed it up in the last sentence, but the clock and latch shoud have been carried through the chip.
Yes, there is a lot info on these chips, people have been wondering the difference for a while. Break the chip open to find out, or the package looks like a dead giveaway.
I am sure they would find their own market if they sold them properly. Imagine buying a similar FAKE7219 for $0.50 rather than a MAX7219 for $6.00+.
I've written drivers for cascadable MAX7219s before so what was your problem?
Based on what Mike said, it sounds like the code attached to the third post of this thread is working reasonably well. The name of the attached archive is "Max7219Demo140116e - Archive [Date 2014.01.16 Time 22.19].zip"
Which 8x8 arrays are you using? I think the above mentioned code is what I used when making the video embedded in this post. The arrays in the video where inexpensive ones sold by ICStation.