max7219 and pic16f627

[Acetronics2]

Hi, Helenevans

And what about power dissipation in the 7219 ??? did you check the maximum current available for the digits ?

No floating inputs ( Ck Enable or so ) ... for 7219 ???

Alain

[helenevans]

hi Alain,
thanks for your reply.
After the Maxim we have a high current circuit to drive the digits.

I just checked with an osciliscope to see what is happening when it has stopped working. The PIC is fine. The Maxims puts all the Segs to ground (therfore, off) and all the Digits are 5v (except, strangely Digit3)

The other thing i noticed is that when the digits starts to misbehave, i can see a lot of noise (or pulsing) in the 5v that goes to both the Pic and the maxim. I have just put a diode in to protect the maxim's 5volt supply and for the moment this seems to have solved the problem. i will post again if this hasn't worked.

best,
helen

[Acetronics2]

and just an idea ...

What if you make transmission a bit slowlier ??? ... (DEFINE SHIFT_PAUSEUS 100 i.e. )

Alain

[mister_e]

<img src=http://www.picbasic.co.uk/forum/attachment.php?attachmentid=439&stc=1>

[helenevans]

thanks for all the responses.
So the problem has come back again. One thing i've done is to re-initialise the maxims, every now and again, so at least they come back to life eventually. but it's far from an ideal solution.

I have put a pause in as Acetronics suggests (although i need the speed) and they do keep going for much longer. but eventually they too, pack up (!)

the speed, yes, maybe this is the issue. i guess most people don't want to change them so rapidly...
Looking at the data sheet, I presume i need to consider the Pulse Width High (which is 50nS)? How can i calculate the right pauses and when to put them, to put the pic in synch with the maxims?
Sorry, i'm sure this is all pretty basic stuff...

any further thoughts, i'd be happy to hear them,
best, Helen

[mister_e]

ARRGH i didn't notice how you did your code...

for digit = 1 to 5
current = LOOKUPl digit, [byt_03,byt_04,byt_05,byt_06,byt_07]
SHIFTOUT datapin, clkpin, MSBFIRST, [digit] 'digit adress
SHIFTOUT datapin, clkpin, MSBFIRST, [current] 'digit data
PULSOUT load1, 3 
next

you must

enable the load line
use the shiftout
disable the load line

how about using something like

for digit = 1 to 5
    current = LOOKUPl digit, [byt_03,byt_04,byt_05,byt_06,byt_07]
    
    LOW Load1
    SHIFTOUT datapin, clkpin, MSBFIRST, [digit] 'digit adress
    SHIFTOUT datapin, clkpin, MSBFIRST, [current] 'digit data
    HiGH load1
    PAUSE 10
    next

but more than likely

for digit = 1 to 5
    current = LOOKUPl digit, [byt_03,byt_04,byt_05,byt_06,byt_07]
    
    LOW Load1
    SHIFTOUT datapin, clkpin, MSBFIRST, [digit,current]
    HiGH load1
    PAUSE 10
    next

EDIT: It remind me a previous post => http://www.picbasic.co.uk/forum/show...tach%2A+max%2A

[helenevans]

hmm, thanks for that.
i was really hopeful, but it still doesn't solve the problem.
I was wondering if its worth getting hold of a max7221, perhaps they are more robust against EM interference?
I have currently testing with two separate rows of 5 digits (each with their own pic). there is definately some kind of current flow problem as when one come on, the other will die etc.

the other post, is interesting as the problem is very similar. However, i have already put the two capacitors between the 5v and the gnd . Any harm in increasing the values?
further thoughts, always welcome