Maxim 7219 driving larger loads
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Posts: 46,084
Hello Everyone,
Believe or not I am still stumped in trying to drive large 4" seven segment
displays with the Maxim 7219... Today I even fried a stamp and I think I
killed the 7219 as well...
In any case, this where I am so far but I will have to wait until the new
Maxim chip arrives to try it again: (I am omitting the grounds, capacitors,
clock, data in, and load and their respective resistors for the sake of
clarity)
5V
|
__|_
d| M |s
i| A |e
g| X |g
i| I |m
t| M |e
o----s| |n
| | |t
| |____|s (a)
o
| |
| |
\ \
/ 10K / 10K
\ \
/ /
MPS2222A MPS2222A
(NPN) (NPN)
| | | |
grnd --o | grnd --o |
| |
| 2N3906
| (PNP)
| | |
| +12V--o |
| |
| ___ |
| | | |
o--common-- |___|(a)
o
cathode | | |
|___| |
|
___ |
| | |
|___|(a)
o
| | |
|___| etc
Problems:
1) I get some over heating on the transistors
2) As I blew both my stamp and 7219 (I think due to a different problem) I
am not sure this works
3) I am having a hard time determining the correct value for the resistors.
4) In this instance, could I run the Maxim from the stamp's VDD?
Thanks in advance (particularly to Eprema for his constant support)
Paul RJ
Believe or not I am still stumped in trying to drive large 4" seven segment
displays with the Maxim 7219... Today I even fried a stamp and I think I
killed the 7219 as well...
In any case, this where I am so far but I will have to wait until the new
Maxim chip arrives to try it again: (I am omitting the grounds, capacitors,
clock, data in, and load and their respective resistors for the sake of
clarity)
5V
|
__|_
d| M |s
i| A |e
g| X |g
i| I |m
t| M |e
o----s| |n
| | |t
| |____|s (a)
o
| |
| |
\ \
/ 10K / 10K
\ \
/ /
MPS2222A MPS2222A
(NPN) (NPN)
| | | |
grnd --o | grnd --o |
| |
| 2N3906
| (PNP)
| | |
| +12V--o |
| |
| ___ |
| | | |
o--common-- |___|(a)
o
cathode | | |
|___| |
|
___ |
| | |
|___|(a)
o
| | |
|___| etc
Problems:
1) I get some over heating on the transistors
2) As I blew both my stamp and 7219 (I think due to a different problem) I
am not sure this works
3) I am having a hard time determining the correct value for the resistors.
4) In this instance, could I run the Maxim from the stamp's VDD?
Thanks in advance (particularly to Eprema for his constant support)
Paul RJ
Comments
segment of the display put a resistor that limits the current to not
more than .05 amps. R=(Supply-.7)/.05. 12 volts - .7 = 11.3 volts
divided by .05 equals 226 ohms. This value can be decreased slightly to
improve brightness if necessary, because the lines are multiplexed.
Hope this helps..
Leroy
Paul Ramirez Jonas wrote:
>
> Hello Everyone,
>
> Believe or not I am still stumped in trying to drive large 4" seven segment
> displays with the Maxim 7219... Today I even fried a stamp and I think I
> killed the 7219 as well...
>
> In any case, this where I am so far but I will have to wait until the new
> Maxim chip arrives to try it again: (I am omitting the grounds, capacitors,
> clock, data in, and load and their respective resistors for the sake of
> clarity)
>
> 5V
> |
> __|_
> d| M |s
> i| A |e
> g| X |g
> i| I |m
> t| M |e
> o----s| |n
> | | |t
> | |____|s (a)
o
> | |
> | |
> \ \
> / 10K / 10K
> \ \
> / /
> MPS2222A MPS2222A
> (NPN) (NPN)
> | | | |
> grnd --o | grnd --o |
> | |
> | 2N3906
> | (PNP)
> | | |
> | +12V--o |
> | |
> | ___ |
> | | | |
> o--common-- |___|(a)
o
> cathode | | |
> |___| |
> |
> ___ |
> | | |
> |___|(a)
o
> | | |
> |___| etc
>
> Problems:
> 1) I get some over heating on the transistors
> 2) As I blew both my stamp and 7219 (I think due to a different problem) I
> am not sure this works
> 3) I am having a hard time determining the correct value for the resistors.
> 4) In this instance, could I run the Maxim from the stamp's VDD?
>
> Thanks in advance (particularly to Eprema for his constant support)
>
> Paul RJ
>
--
*******************************************************
* \\|// *
* ( @ @ ) *
*----oOO--(_)--OOo
*
* Leroy Hall, Senior N8VRC *
* Instructor / Trainer -- Computers & Electronics *
* Email: leroy@f... *
* Web Page: http://home.fuse.net/leroy/ *
* Phone: (513) 697-7539 317 Cherokee Drive *
* Pager: (513) 691-4361 Loveland, Ohio 45140-2404 *
* Oooo. *
* .oooO ( ) *
* ( ) ) / *
* \ ( (_/ *
* \_) *
*******************************************************
1) First of all, you could have fried the voltage regulator on the
stamp if you hooked the huge LED display up to it. If you need more
than 50mA of current total, you'll need an external voltage
regulator. They're fairly cheap and easy to use.
2) How much current does this display use up? If each individual
SEGMENT, not the whole thing, is less than 35mA, you may want to
consider switching to using a 74HC595 shift register instead. I just
figured out how to use them, and they're fairly simple. The whole
thing takes 3 stamp IO's and you'll need one chip for each digit
(about $0.50 ea) but you can daisy chain as many as you need together.
Just a thought. I really don't know all that much about the LED
driver your using.
-Chris
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>>>
Meassage 24 Date: Sun, 30 Apr 2000 18:16:11 -0400
From: "Paul Ramirez Jonas" <prjnyc@m...>
........
Problems:
1) I get some over heating on the transistors
2) As I blew both my stamp and 7219 (I think due to a different problem)
I
am not sure this works
3) I am having a hard time determining the correct value for the
resistors.
4) In this instance, could I run the Maxim from the stamp's VDD?
<<<<
Paul, I need to know you the characteristics of your LED -
1. How many digits?
2. What is the _static_ current _per segment_?
3. What is the _static_ voltage _per segment_?
4. What is the scan frequency? [noparse][[/noparse]I'm not directly familiar with the
MAX 7219 but gather it's a multiplexed driver].
What I suspect is happening is that your PEAK currents are exceeding
the capabilities of the '3906 &/or '2222.
The transistors should be driven to saturation by adequate base drive
and perhaps in combination with current limiting by resistor in series
with each segment.
How to do this depends on the LED characteristics which I don't know.
E.g. if you have an average duty cycle of 10% and current of 50ma then
the peak current is about 500ma. That means that if you are driving the
base of the transistor with .5 ma [noparse][[/noparse]10000 ohms 5 volts +/-] you'll
need a DC HFE of 1000 to saturate the transistor - and that HFE is at
500 ma not 50 ma!
Yes, once you isolate the power parts from the signal parts you can
use the Stamp Vdd for the 7219 - assuming you are not exceeding the
Stamp supply current limits. This accomplished through high DC
current gain between the MAX7219 and the LEDs...
Hope this makes things clearer... or points in the right direction,
premena
________________________________________________________________
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The large LEDs have data sheets at
ftp://ftp.jameco.com/data_sheets-displays/105591p1.gif
and
ftp://ftp.jameco.com/data_sheets-displays/105591p2.gif
The second page includes the information about the power requirements... I
am not sure how to read it. I will have four of these.
Depending on the supply voltage the Maxim chip scan frequency varies between
1150Hz (at 4V) and 1350Hz at 6V.
And to make things clear the Stamp and Maxim where blown not because of the
set up but due to 'human error'. Hint: sometimes 12V looks just like 5V.
Thanks,
Paul
>Paul, I need to know you the characteristics of your LED -
>
>1. How many digits?
>
>2. What is the _static_ current _per segment_?
>
>3. What is the _static_ voltage _per segment_?
>
>4. What is the scan frequency? [noparse][[/noparse]I'm not directly familiar with the
> MAX 7219 but gather it's a multiplexed driver].
>
>What I suspect is happening is that your PEAK currents are exceeding
>the capabilities of the '3906 &/or '2222.
>
>The transistors should be driven to saturation by adequate base drive
>and perhaps in combination with current limiting by resistor in series
>with each segment.
>
>How to do this depends on the LED characteristics which I don't know.
>
>E.g. if you have an average duty cycle of 10% and current of 50ma then
>the peak current is about 500ma. That means that if you are driving the
>base of the transistor with .5 ma [noparse][[/noparse]10000 ohms 5 volts +/-] you'll
>need a DC HFE of 1000 to saturate the transistor - and that HFE is at
>500 ma not 50 ma!
>
>Yes, once you isolate the power parts from the signal parts you can
>use the Stamp Vdd for the 7219 - assuming you are not exceeding the
>Stamp supply current limits. This accomplished through high DC
>current gain between the MAX7219 and the LEDs...
>
>Hope this makes things clearer... or points in the right direction,
>premena
Original message
Hello Everyone,
Believe or not I am still stumped in trying to drive large 4" seven segment
displays with the Maxim 7219... Today I even fried a stamp and I think I
killed the 7219 as well...
In any case, this where I am so far but I will have to wait until the new
Maxim chip arrives to try it again: (I am omitting the grounds, capacitors,
clock, data in, and load and their respective resistors for the sake of
clarity)
5V
|
__|_
d| M |s
i| A |e
g| X |g
i| I |m
t| M |e
o----s| |n
| | |t
| |____|s (a)
o
| |
| |
\ \
/ 10K / 10K
\ \
/ /
MPS2222A MPS2222A
(NPN) (NPN)
| | | |
grnd --o | grnd --o |
| |
| 2N3906
| (PNP)
| | |
| +12V--o |
| |
| ___ |
| | | |
o--common-- |___|(a)
o
cathode | | |
|___| |
|
___ |
| | |
|___|(a)
o
| | |
|___| etc
Problems:
1) I get some over heating on the transistors
2) As I blew both my stamp and 7219 (I think due to a different problem) I
am not sure this works
3) I am having a hard time determining the correct value for the resistors.
4) In this instance, could I run the Maxim from the stamp's VDD?
Thanks in advance (particularly to Eprema for his constant support)
Paul RJ