MB64e will never ever work, no way

MIDIbox HUIs
1

Of course I’m just kidding, but please explain:

If you have 16 LEDRINGS with 11 LEDS each, and all are turned on,

then the current flowing into the common cathode pin is, during

each 1/16 time interval, 11*(5v-2v)/220 = 11*14mA = 154 mA.

But the 74HC595 is specified for 25mA input current at any voltage.

Why does it work? Where is my blind spot?

Or is the 25mA number only valid if all pins carry that current at the same time?

Yours,

Melonenmonster

2

Whats the point of a ledring with all the leds turned on? arent they usually used by turning on one led to show the position? ???

3

Whats the point of a ledring with all the leds turned on? arent they usually used by turning on one led to show the position? ???

no i think the ledrings we use have all leds on if the value it represents is maximum, no leds on when value is minimum (like a meter)

@melonenmonster; dunno why, but it works of course

cheers, marcel

4

My mistake, I’ve never seen them in action! Sorry!  :-X

5

I just wanted to add that I’m not asking just for fun, but because I need to get the maximum brightness

out of the LEDs and thus need to know by what the currents are limited and how much I could push it.

Melonenmonster

6

I believe, that the switching is done, in a vertical way (when you look at the pdf) http://www.ucapps.de/midibox_lc/midibox_lc_ledrings_meters.pdf. This way there is only one LED active per Input pin at the time.

Greets, Roger

7

That’s true for the LED side connected through resistors with the Outputs.

But the other pin of the LED is also connected to an Output of the 74HC595.

So, since all pins of the LEDs are connected to the serial register outputs,

if you have a row or a column of LEDs active at the same time means that

in any case a single output must handle multiple active LEDs.

Melonenmonster 

8

hi,

I think you make a valid point. As the cathode driving pin reaches its maximum current sinking of 25mA or thereabouts the voltage on this pin will increase which means less current through each LED.

If this is the case, then the brightness of LEDs in a column will gradually decrease as each additional LED is turned on. It may be not very noticable.

(btw; I think the LED rings can operate in different modes so you can have single dot being displayed if you want.)

two solutions I can think of:

  1. use high output LEDs (say 100’s of mcd) and increase 220R to 1.5k -> (5-2)/1.5k=2mA per LED

  2. put a darlington array such as ULN2003 in front of the column driver. You’d have to invert the DOUT signals to these driver lines in the firmware (not hard to do, I believe).

cheers

9

Duggle,

you made my day. Not only did you explain what

happens, but also made a very clever proposal.

I thought of some kind of amplification, but that

ULN2003 is really convincing. I didn’t do electronics

for many years, so I’m not aware of the current

elements base and would have to search a lot.

I’ll setup a test, It’ll take some time,

but I’ll let you know.

Thank you.

Yours,

Melonennmonster

10

Another thing to think about is if you connect many LED’s, lets say for worst case 128 LEDs. And every LED is drawing approx. 15mA. Then all LEDs (if ON) draw a total of 1,92A !!. Thats a to high current to draw from the core in a tiny flatcable to the DOUT boards. Also the regulator on the core can’t deliver this current.  ???

Or is there something I miss here ?

/Wise