Show Posts
Pages: 1 [2] 3 4 ... 57
16  Using Arduino / LEDs and Multiplexing / Re: How to troubleshoot max7219? on: October 01, 2012, 11:30:41 pm
Okay, so given that things appear wired correctly:
What value is Rset?
Is Vcc at 5V?
Is the matrix installed upside down?

Rset is 18k.   The device package says "1802", and on the two boards I assembled, I measure 18.1 and 18.8k.  The 18.8 surprises me because they are supposed to be 1% precision resistors, but should still work fine.

I do have 5V on Vcc.

The first time I mounted the matrix to the wrong side of the board (actually the side I intended but I did get the header rows backwards on the PCB), the second time I installed on the opposite (electrically correct) side and I just double checked it's in the right way around.
17  Using Arduino / LEDs and Multiplexing / Re: How to troubleshoot max7219? on: October 01, 2012, 10:41:41 pm
I'm seeing pins connected together here.
Can you confirm with the art work if these are connected?

MATRIX1  16       8        8          1
         IC1      2        DIG0       1
MATRIX13 1        8        8          1
         IC1      21       SEGE       1

I am not totally clear what this means.  I can confirm (on the printed board with a meter as well as looking at the board file in eagle) that IC1 pin 2 connects to pin 8 on the correct jumper to it's in the right spot for my matrix.  IC1 pin 21 connects to pin 8 on the other jumper, directly across the board from the first one, again correct for my matrix.   And pin's 2 and 21 are not connected to each other.

Edit:  I understand now what you were saying that it's the same pin number on the jumper/header row so they'd be connected together.  It's a different header on the board and the right pin on the IC does go to the right header and they're not connected together.  I don't know why the netlist looks like that, is it the first column (1 vs 16) that defines them as separate devices?
18  Using Arduino / LEDs and Multiplexing / Re: How to troubleshoot max7219? on: October 01, 2012, 08:16:31 pm
Sorry for the delay, my schematic from eagle is:

and my netlist is

The schematic is a very basic implementation right off the datasheet, the jumpers on the left are for signal in from the MCU and out to the next identical board to have several matrices.   The jumpers on the right go out to the matrix. 
19  Using Arduino / LEDs and Multiplexing / Re: How to troubleshoot max7219? on: September 30, 2012, 10:26:47 pm
I've gone over my eagle schematic very carefully and checked every connection on my pcb with a multimeter and couldn't find any problems.  I also assembled a second board from scratch just in case it was an assembly defect and I have the exact same result.  This is a very frustrating problem.

At this point, I want to say the only possible problem is the max7219's are defective.  I bought them on eBay and paid $7 for a 10 pack which is I realize is very cheap.  So I'm wondering if I should try and buy one from a more reputable source, but I'm not sure where to try.  I also am considering buying some SOIC to DIP pcb's to try dropping one of the chips into a working circuit on a breadboard.  Is there no better way to see if the SOIC IC is any good?
20  Using Arduino / Programming Questions / Re: A handy hint? or not. on: September 27, 2012, 12:57:52 pm
if ((millis() & 0x1ff) == 0) {

If your loop takes more than half a millisecond or so, won't you miss some of the times the last 9 bits of millis() are 0?  It seems you'll have your println at some pseudo-random multiple of half a second.

21  Using Arduino / LEDs and Multiplexing / Re: How to troubleshoot max7219? on: September 21, 2012, 11:23:25 pm
I've been going over my schematic, comparing to the datasheets, my .brd file and the physical board with a continuity tester and so far I don't see any problems.  I'm worried that I might have a problem because I bought the cheap eBay max7219's and now I have no clue how to diagnose it.  I can post the schematic but since I used a bus on the outputs I don't think it will be very helpful.
22  Using Arduino / LEDs and Multiplexing / How to troubleshoot max7219? on: September 21, 2012, 09:43:09 pm
I have a max7219 based project working perfectly on breadboard with a DIP version of the MAX7219.  I had some PCB's made with the same schematic using the SOIC version of the MAX7219.  I assembled the first board, it doesn't work and I have no idea where to begin troubleshooting a soldered board so I was hoping someone here could help.

There is one LED always on and very bright and the rest of that row is on normal brightness.  When I try to control the display, I see LEDs changing but can't see how it correlates to what I'm telling it to do.

If I connect power to the MAX7219 board only that LED lights.  I've checked the obvious things like shorts on the outputs going to that LED and the connections are fine.  I don't know what to do next.  I can assemble the next board, maybe this chip is defective but that seems like a long shot.  I've thought about soldering my working dip chip with wires to the SMD pads just to prove the rest of the board works, but that's a pretty big job and I'm not sure what I'll learn.

Thanks for any suggestions you can give. 
23  Using Arduino / General Electronics / Re: Cutting Female Headers on: September 13, 2012, 07:04:50 pm
I have found these work great for ICs but don't admit larger pins like the ones on LED matricies.  So be forewarned on that.

Great, I have these on order right now for some LED matrices.  I guess it also won't admit the larger headers in an arduino nano then which is the other thing I wanted them for..   
24  Using Arduino / General Electronics / Re: Cutting Female Headers on: September 13, 2012, 05:37:10 pm
I use wire cutters too, and then file the edge so it looks better.

You can also use, which looks easier to snap.
25  Using Arduino / Programming Questions / Re: How accurate are delays within loops on: September 12, 2012, 07:27:13 pm
I am only trying to store about 100 points which would theoretically be 2.5 seconds at 40 values per second. Afterwards I would upload them to the computer and wipe the old values.

Why can't you store the 100 bytes in SRAM then until you upload it to the computer?  The only reason to use EEPROM is if you want the values to persist through the Arduino being reset.
26  Using Arduino / Programming Questions / Re: Can I burn the bootloader(UNO) to a new atmega328 using UNO? on: September 08, 2012, 01:28:45 pm
You could link the page you're talking about?  Maybe tell us what techniques you're thinking of?

The Arduino UNO still has the 6-pin ICSP header, so why couldn't you burn a bootloader to a blank ATMEGA328?
27  Using Arduino / LEDs and Multiplexing / Re: Multiplexing dual 7segment diplays on: September 08, 2012, 01:18:10 pm
You can use a 74595 as you describe, 1 chip per digit and load all the bits as needed for common-anode or common cathode each time you want to update the display.   Or you can use a single 74595 to drive the segments, and an IO pin (with a transistor) for each digit and quickly scan through all the digits repeatedly; that's a bit easier hardware-wise, a bit harder code-wise.

There are also chips like the 7447 which will take your digit in BCD on 4 inputs and decode the 7-segment font to drive a single digit.

The easiest way, in my opinion, is to use a MAX7219 which will drive up to 8 common-cathode digits from a single chip needing 3 IO pins on your controller.   You simply set the values the digits should display and the chip takes care of the rest including constant current drive.  There is an LedControl library available which makes this route extremely easy.
28  Development / Suggestions for the Arduino Project / Re: Mini-Shield form factor? on: September 08, 2012, 11:35:18 am

Interesting.  I've been playing with eagle and carefully measuring my Diecimila and some shields I had made using the 10x10 service.  It looks like the headers  are 1.9" apart and 50mm is 1.968 inches, so I should have 0.8mm minus 1/2 the drill size on the outside of my header (mixing metric and imperial is not fun).  The standard square posts in headers are 25mil, or 0.635mm, so I don't think I should use a drill size smaller than 0.8mm.

That actually does let me have some board material left around the hole, thought it's cutting it awfully close and in your image it looks like he as a lot more than my estimate.

It's definitely worth giving it a try next time I need a shield, because as I said even if I end up with my holes split, the board will still work.
29  Development / Suggestions for the Arduino Project / Re: Mini-Shield form factor? on: September 08, 2012, 01:45:46 am
Don't quote me, but I'm pretty sure I've seen shields done on the 5 cm square boards.  The header pin holes are awfully close to the edges, but they appear to fit.

I believe that might be possible if you basically solder the headers along the outer edges of the board, maybe have drill holes that are broken open by the edge of the board as guides.  I couldn't find anything about it though.  If you have any links, I'd love to see how it came out.
30  Development / Suggestions for the Arduino Project / Re: Mini-Shield form factor? on: September 06, 2012, 10:40:40 pm
This idea is something I've thought about for a while.  Mainly because seeedstudio's $10 PCBs are 1.9" square and the arduino shield needs to be 2.1" to span both rows of headers.  That extra 0.2" raises the price from $10 to $25.   I considered an adapter that I'd only have to make once for unlimited mini-shields but it will be annoying to have the extra layer just to use non-standard shields.

The other thing I've thought of is making an oversized adapter shield that will have spots for 4 mini-shields, replicating all or some of the IO multiple times, so as long as you're careful of which pins you use on each mini-shield, it should make modular design easier.  That still misses the whole point of wanting to do quick cheap easy shields though.
Pages: 1 [2] 3 4 ... 57