led MATRIX CURRENT DRAW

[be80be]

I really said that wrong you want the resistors on the column's not the ROW but I did mean you maybe have that backward which looks like you did and what Jon is telling you is the more leds you light there no way to do that these LED Matrix where made to light one dot at a time.
View attachment 67997
Now if at the top left you set high portC.0 and low portb.0 the first led lights. Turn that one off and go for the next.

I see now how you got all out of whack you looked at grams game then hooked resistors to the rows as he did then you tried to light a whole row at a time which places the leds parallel which could work but the resistor limits the power and divides it not evenly and if you change value when a led is off, You light 2 of them your power to them goes threw the roof. Like 5 you see 20mA and 2 you see 100mA. Not a good idea

 

[MrDEB]

I have tried turning on ONE LED at a time as was suggested but its very dim. Tried at 10ms. BUT with the LEDs not getting full current of 20ma they will be DIM. Perhaps thas why the 10ms delay looks like crap.
Going to wait from the parts from Digikey and see what I get. I turned on two segments in one row and yes the current was almost 60ma but I was running with 8v using a transistor. I do not plan to light up more than two leds per row. My original design had 220 ohm resistors on the rows. That is no longer what I am using. The schematic I posted is where I am at this point.
I told Jon on several occasions I AM ONLY GOING TO USE THE LED MATRIX for durability issues. He didn't understand english or ?? he kept bring it up as usual.

 

[JonSea]

I told Jon on several occasions I AM ONLY GOING TO USE THE LED MATRIX for durability issues. He didn't understand english or ?? he kept bring it up as usual.

MrDeeb, perhaps I have a better understanding of your (lack of) skills than you do. You certainly don't let a complete lack of understanding influence your thought process.

If you had read my last post (you do know how, yes?), you would have seen that the entire thing was directed at using your (free samples from Kingbright) LED matrix. Oh, since you failed to notice that, let me put it here for you:

The matrix MrDEB apparently has has two LEDs in series for each dot. The typical Vf is 4 volts, but the maximum is 5 volts. He needs to design around the 5 volt worst case to be sure the dots will illuminate.

What MrDEB is refusing to believe is that each dot must be driven via its own resistor. No exceptions to this rule - LEDs cannot be used in parallel from a single resistor. Thus, MrDEB's current measurements with 1 - 5 LEDs driven from a single resistor is meaningless. They won't work like that!

MrDEB's situation is complicated a bit by the high forward voltage of the matrix he has, but just a bit.

The first step which really must be understood is the basic circuit of a multiplexed display. Think way back to the beginning of this mess. Seven port pins driving the anodes of the rows via a resistor. Five cathodes connected to ground via a ULN2003. Keep this circuit in mind. Yes, I know the 5 volts from a PIC won't drive the matrix MrDEB is attempting to use. Just assume a matrix with Vf = 2.2v and the resistors sized for a current flow of 25 mA per LED.

Now, lets say that all seven anode pins are high, and one and only one cathode, the first column, is conducting to ground. What have we got in this case?

1. All of the LEDs in column 1 are illuminated.

2. Each port pin is supplying 25 mA to its associated LED.

3. The ULN2003 is sinking all the current through the LEDs to ground, namely 7 x 25 mA = 175 mA.

Everyone is happy as long as exactly one cathode is active.

What happens if we quickly alternate between cathode 1 active and cathode 2 active? The dots in the first two columns will be evenly illuminated. And if we quickly switch from 1 to 2 to 3 to 4 to 5 and continue the cycle? All of the dots will be evenly illuminated. They won't be as bright as when we had only one column illuminated because each column is only on 1/5 of the time.

Be sure to notice that only one cathode is active at a time, and each port pin only drives one LED at a time.

So how do we display a symbol on the display? Let's consider a T five dots wide and seven dots tall.

1. With all cathodes off, we set only the anode connected to the top dot high (the pattern in the first column)
2. We active the cathode in column 1 for a short period of time, say 10 mS as a guess.
3. Turn off the cathode for column 1.
4. Set the anodes for the patern in column 2, namely just the upper dot.
5. Turn on the cathode for column 2 for 10 mS
6. Turn off the cathode for column 2.
7. Set the anodes for the pattern in column 3, namely all on.
8. Turn on the cathode for column 3 for 10 mS.
9. Repeat the process for columns 4 & 5.
10. Repeat the entire process.

Notice only a single cathode is every on and each anode supplied exactly one dot.


But, but, but......

Yes, MrDEB's displays are red and green. This just means there are ten cathodes instead of five. An additional ULN2003 is needed (and 5 more port pins to control it) but the same principles apply. Only one cathode is active at a time.

But, but, but.....

Yes, the display MrDEB has requires greater than 5 volts to operate. Add one of the driver chips the be80be or I listed to driven the anodes. This may flip around high/low on/off but the principles are still the same. One cathode active and each gate of the high side driven supplies exactly one LED.

Do note that the current draw is (LED current) x (max number on in a column). With a current of 25 mA per LED, this could be as high as 175 mA, not agreeable to a 9 volt battery or even 6 AAA cells.

MrDEB, this is the straight scoop. Don't get creative with things you don't understand.

The really important thing you refuse to believe is the LEDs cannot be operated in PARALLEL. Each LED must have its very own current limiting resistor. One LED, one resistor. No LEDs connected in parallel with a single resistor, ever.

Understanding that is essential to using a matrix display. Let me say it again since you've ignored it numerous times already.

No LEDs connected in parallel with a single resistor, ever.

One LED. One resistor.

One LED. One resistor.

One LED. One resistor.

Why is this? LEDs will not share current nicely. Period.

Here's some help:

**broken link removed**

So you've ignored Brad's unbelievable efforts to help.

You've even failed to acknowledge Mike's comments, questions and offer to create a circuit for you.

You've ignored Burt's offers to help.

And you've ignored all of my comments, including two complete discussions of the required steps to use a multiplexed display.

Do you think none of the four of us understand what you're trying to do? Really?????

 

[be80be]

If you look at this picture in the post you could light the Red leds at the same time If you can sink 166.5 mA

You can't light all the blue you'll run out of power the resistor limits it to 33 mA so one led may light but the rest will not if two lights then your leds are not droping 4 volts I f you raises the voltage to light all leds then If you light just one or two maybe three you'll more the likly blow a led or two or three.
Don't hook it to a port use 7 NPN's on portB too sink not shown in picture
View attachment 68013

 

[JonSea]

Burt's red LEDs each have a current-limiting resistor. These can all be illuminated at the same time if each port pin is configured correctly.

If you make the resistor small enough to get enough current to light each blue LED at the desired level...you'll let the smoke out. LEDs aren't exactly the same. The one with the lowest forward voltage will grab most of the current.

This effect is easy to see with an RGB LED. if a constant current source is connected in parallel across the red, green and blue elements, all you're likely to see is a bright red LED since its forward voltage is the least. You may see a dim light from the green LED but the voltage is clamped to the forward voltage of the red LED and the blue will never see enough voltage to turn on.

Sorry, I know MRdeeb doesn't like explanations, but some may find it useful.

 

[MrDEB]

I stated that I have one resistor per colum(cathodes) and no resistor on the row (anodes) AND ONLY enabling one row at a time. So in fact I have say two LEDs on with two resistors (one per LED). YES IF I enabled all 5 LEDs in one row I have 125ma current draw but all the 5 LEDs will be at full brightness running at 25ma each. BUT only for 10-20ms before the next row is enabled and turn off the previous row.
I don't plan on running 5LED per row at one time. That was a demo test.
My first design HAD 220 ohm resistors on each row(anodes) but on the last schematic the resistors are on the colums BUT only one LED per colum on at a time.

 

[JonSea]

I stated that I have one resistor per colum(cathodes) and no resistor on the row (anodes) AND ONLY enabling one row at a time. So in fact I have say two LEDs on with two resistors (one per LED). YES IF I enabled all 5 LEDs in one row I have 125ma current draw but all the 5 LEDs will be at full brightness running at 25ma each. BUT only for 10-20ms before the next row is enabled and turn off the previous row.
I don't plan on running 5LED per row at one time. That was a demo test.

My first design HAD 220 ohm resistors on each row(anodes) but on the last schematic the resistors are on the colums BUT only one LED per colum on at a time.

Ok then. You know everything. So why isn't it working?

I am truly sorry I have tried to help you. Sorry I pointed out that whatever you described was wrong and wouldn't work. Sorry to have troubled you with all those explanations in the hopes that you might learn something. Sorry to have upset your fantasy world where things work because you want them to. I am sorry to have wasted all your time.

It won't happen again. You have yourself a nice day.

 

[MrDEB]

I am not saying your right or wrong.
Here is an example schematic which is pretty much exact what I am doing.

**broken link removed**
using a UDN2982 which is the same as the TD62783APG
this guy is using 18-20v where as I am only going to use 7v. He is scanning the displays using 80ma dividing by 4 displays = 20ma.
An his project works.

 

[JonSea]

Perfect. Perhaps he'll be your next victim? I think you've just about bled everyone here dry.

By the way, the link you posted is exactly the circuit I described again in post #103. Sorry all the explanation kept you from understanding.

Watch your necks guys. See you around.

 

[be80be]

He not doing what your doing Doug 7 segment leds are like having 7 leds by there self for a total of 28 leds
you have 70 leds and you can't fire 7 at time he can. Only one so you give that one up to 40mA flash and go to the next one and see how it goes.

 

[Mike - K8LH]

I am not saying your right or wrong.
Here is an example schematic which is pretty much exact what I am doing.

**broken link removed**
using a UDN2982 which is the same as the TD62783APG
this guy is using 18-20v where as I am only going to use 7v. He is scanning the displays using 80ma dividing by 4 displays = 20ma.
An his project works.

Hey Doug (MrDEB), the guy who designed that project knows what he's doing. You should pay particular attention when he says;

Because of multiplexing 4 modules to get an average current of 20mA per segment the current has to be four times higher ( 20mA x 4 = 80mA ).

This brings up a fundamental design consideration that I suspect you may have overlooked. Please consider that there are a number of ways you might drive your multiplexed 7x10 matrix;

(A) one row by five columns with fourteen cycles to refresh the entire display (7.1% duty cycle)
(B) one row by ten columns with seven cycles to refresh the entire display (14.2% duty cycle)
(C) one column by seven rows with ten cycles to refresh the entire display (10% duty cycle)

If you're designing a full brightness display with 20-mA "average" current per segment you'll need to provide ~280-mA "peak" current per segment at a 7% duty cycle, or ~140-mA "peak" current per segment at a 14% duty cycle, or ~200-mA "peak" current per segment at a 10% duty cycle. I haven't seen any displays that can handle more than 100-mA "peak" current per segment. And so, duty cycle becomes a fundamental consideration when designing any matrix display because it directly translates into your ability to meet LED "peak" current specifications. Which BTW is why I recommended multiplexing configuration 'B' with its much higher duty cycle back in post #29.

Now consider current requirements for driving configurations A, B, and C above. For configuration 'A' each pin on your sourcing row driver needs to provide up to 1400-mA "peak" current for five (280-mA "peak") column LEDs. Configuration 'B' also requires up to 1400-mA "peak" current for ten (140-mA "peak") column LEDs. Unfortunately, none of the sourcing driver ICs you've looked at can handle 1.4 Amps "peak" current. Configuration 'C' would require each output on the sinking row driver IC to handle up to 1400-mA "peak" current for seven (200-mA "peak") row LEDs. Again, the sinking driver ICs you've found cannot handle that much current.

Fortunately, the prognosis is not as gloomy as it sounds. Since you're using a very high luminous display, I suspect you'll find that ~14-mA "average" current per segment is nearly as bright as 20-mA "average" current per segment. This can be achieved by using method 'B' with its 14% duty cycle, seven NFET/PFET pairs on the anode rows capable of sourcing 1000-mA "peak" current to ten column LED segments, and a pair of TLC5916's connected to the ten cathode columns. Bias the matrix for ~100-mA "peak" current per LED segment (~14-mA "average" current), and you're in business.

I'd also like to point out that Jon's suggestion for using thirty five discrete red/green LEDs has merit. All it would take is five TLC5916, or similar, sinking driver ICs to drive all of the LEDs at 100% duty cycle with 20-mA "average" current.

Food for thought.

Regards, Mike

 

[MrDEB]

I fully understand what your saying Mike. I hopefully am only going to enable two LEDs at a time via the anodes. Only utilizing the red colums separate from the green colums.
So selection B 14.2 duty cycle x 2 = 28.4 duty cycle if I am interpreting it right?
BUT I am not going to enable all the 35 leds. Each routine enables 5 LEDs per routine but only 2 max at any one time.
I admit I am the last person to converse about math but just curious if possible about the 280ma max?
If I have two leds ON in one row at 20ma does that not equal 40ma. Or am I missing a crucial math equation?
LOST as usual

 

[MrDEB]

Now I am really LOST

Because of multiplexing 4 modules to get an average current of 20mA per segment the current has to be four times higher ( 20mA x 4 = 80mA ).

I have 5 segments per row so 5 x 20ma = 100ma max.
This is getting confusing.
The link I posted was exactly what I have been describing. My schematic I posted is the same but without the High Side driver you suggested which I have ordered.

 

[Mike - K8LH]

Hi Doug,

Are you saying that you're only lighting patterns of five LEDs at any one time? If so, you could use that to great advantage to increase duty cycle and brightness. Could you elaborate, please? What patterns are you going to generate? I'm really very interested and very puzzled about your project. For example, I imagine you're building the display to use for right and left turn signals and brakes, but since those are always red I can't imagine why you would need green or yellow colors.

As for your other questions, I'm a bit lost. Please let me study to see if I can figure out what you're asking. Thanks.

Regards, Mike

 

[MrDEB]

The red leds for signaling a progressive arrow pointing either left or right.
The green will just be blinking as a n indicator to vehicles that HERE I AM.
I have a video of what I am refering to. Let me locate.

 

[Mike - K8LH]

Now I am really LOST

Because of multiplexing 4 modules to get an average current of 20mA per segment the current has to be four times higher ( 20mA x 4 = 80mA ).

I have 5 segments per row so 5 x 20ma = 100ma max.
This is getting confusing.
The link I posted was exactly what I have been describing. My schematic I posted is the same but without the High Side driver you suggested which I have ordered.

Basically, only one digit in that four digit display is on at any time. The first digit is lighted, then the second digit, then the third digit, and finally the fourth digit. Each digit is on for 1/4th of the time that it takes to refresh the entire display. That's a 1/4th or 20% duty cycle. The designer wants to drive each LED in the display with 20-mA "average" current for full brightness but since each LED is only on 1/4 of the time he needs to bias the LED so that it's lighted with X = 20-mA / (1/4) = 80-mA current. Does that help?

Regards, Mike

 

[MrDEB]

rough idea I am doing

here is a video of my basic idea.
The POV using LEDs is kinda out the widow dut to the LEDs being dim.
**broken link removed**
Really a rough idea but it shows the progressive idea I am trying to achieve.
Only a maxium two LEDs per row on at any one time. This may change ??

 

[MrDEB]

Houston we have LIFT OFF!!

Well I connected the LED High Side driver and the LEDs are brighter BUT need to change some resistors and as Mike pointed out duty cycle(presently set at 10MS)
The high side driver TD62783APG controls the ROWS
at present I have the ULN2803 on the cathodes w/ a 220 resistor.
one row enabled: 1 colum = 12.4ma
2 colums = 22.9ma
3 colums = 32.8ma
4 colums = 42.3ma
5 colums = 51.2 ma
1 ROW, 2 COLUMS alternating back and forth w/ DELAYMS(10) = 12.3ma
Now I get what Mike was referring to about duty cycle

Conclusion dim LEDs screw up the POV idea. Been there done that
contemplating finish up the code THEN experiment with the TLC5917 Constant Current Sink. This might eliminate all the resistors down to one. Goes in place of the ULN2803.
Looking over the matrix cube description of how the current sink is set up I might just take a whack at it.

 

[be80be]

Why

Looking over the matrix cube description of how the current sink is set up I might just take a whack at it.

I told you how it was wired and I made this one and It doesn't have any chip diving it just npn's sinking
[video=youtube_share;OsUJwhyjJJc]http://youtu.be/OsUJwhyjJJc[/video]

And the room has enough lights on to find a nat you no what in. It was bright

And believe it or not there only one led on at a time just scanned fast in loops so you can see them

 

[be80be]

Here a 5x7 led matrix and yes it's POV only one led on for 500uS then it's totally shut off for 100uS next led is loaded and switch on then the same for the next till all five have flashed for 500uS each in a loop.

Yes it's POV one led at time and there getting 25 mA each

And the same leds in the dark[video=youtube_share;54cIqr-d0d8]http://youtu.be/54cIqr-d0d8[/video]
Dang there all the same brightness

And Doug i reassure you this is POV there one led flashing at a time in a loop and it looks like there all on to your eyes.

P.S. one more thing these leds are powered by the port pins only.
7 pins are sinking and 5 pins sourcing