Melonenmonster Posted April 1, 2005 Report Share Posted April 1, 2005 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, duringeach 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 Quote Link to comment Share on other sites More sharing options...
stryd_one Posted April 1, 2005 Report Share Posted April 1, 2005 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? ??? Quote Link to comment Share on other sites More sharing options...
illogik Posted April 1, 2005 Report Share Posted April 1, 2005 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 coursecheers, marcel Quote Link to comment Share on other sites More sharing options...
stryd_one Posted April 1, 2005 Report Share Posted April 1, 2005 My mistake, I've never seen them in action! Sorry! :-X Quote Link to comment Share on other sites More sharing options...
Melonenmonster Posted April 1, 2005 Author Report Share Posted April 1, 2005 I just wanted to add that I'm not asking just for fun, but because I need to get the maximum brightnessout of the LEDs and thus need to know by what the currents are limited and how much I could push it. Melonenmonster Quote Link to comment Share on other sites More sharing options...
Screaming_Rabbit Posted April 1, 2005 Report Share Posted April 1, 2005 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 Quote Link to comment Share on other sites More sharing options...
Melonenmonster Posted April 1, 2005 Author Report Share Posted April 1, 2005 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 thatin any case a single output must handle multiple active LEDs.Melonenmonster Quote Link to comment Share on other sites More sharing options...
Duggle Posted April 2, 2005 Report Share Posted April 2, 2005 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 LED2) 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 Quote Link to comment Share on other sites More sharing options...
Melonenmonster Posted April 4, 2005 Author Report Share Posted April 4, 2005 Duggle,you made my day. Not only did you explain whathappens, but also made a very clever proposal.I thought of some kind of amplification, but that ULN2003 is really convincing. I didn't do electronicsfor 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 Quote Link to comment Share on other sites More sharing options...
Wise Posted April 6, 2005 Report Share Posted April 6, 2005 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 Quote Link to comment Share on other sites More sharing options...
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