looking for a led driver board

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dacflyer
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looking for a led driver board

Post by dacflyer »

i have a 4 digit 7-segment led display i built long time ago,, each segment uses bout 9v. the displays are 2.3"
i was using a 7107 IC and 2003? driver buffers..been using it as a giant volt meter set up and a LM34 temp sensor , so i thus have a big old temperature reading.. how ever the unit never worked quite right.. reading were always skewed a bit..was not linear.
so i got tired of it, and i wan to make me a new display that is arduino controlled.
i have looked at the small boards offered by SPARKFUN
https://learn.sparkfun.com/tutorials/la ... okup-guide
would be a good choice, but the output resistors are way too small and would over power the leds.
i need something like this board, but with lower output voltage..
i had some before and it was really hard to change out the super small chip resistors, i had 1/8W resistors i used, but you figure 8 resistors per board ( display ) and the job gets old very quickly...

any suggestions...now the board you can run separate voltage for the segments, aside from the 5v logic for the chip..but i can't get it right, unless i build a variable regulator for it.. fitting and wiring the leds to the board is also a choir.. fitting is usually the bigger problem..
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Janitor Tzap
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Re: looking for a led driver board

Post by Janitor Tzap »

Have you thought about using Resistor Arrays; DIP's or SIP's?
Image
Image
Image
Saves you from the hassle of mounting individual resistors. :smile:
Plus, the space saving on the PCB.


Signed: Janitor Tzap
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

hadn't thought bout that, not sure pin spacing would meet up.. would have to be a dip style,,
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haklesup
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Re: looking for a led driver board

Post by haklesup »

I'm trying to figure out that sparkfun board. I tried to look up the IC part number. The first line (34ANPET) came up with nothing but 6C596 comes up with a shift register. I guess a shift register makes sense if you are driving multiple LED segments serially. Still the whole schematic is not materializing in my head yet but it seems to be on page 15.

http://www.ti.com/lit/ds/symlink/tpic6c596.pdf

Since the outputs are open Drain, the current to the LED segments is simply your supply voltage through the Resistors. If you feel the net power is too high, you can probably reduce the 12V supply easier than you can replace the resistors. However, I think you can also replace Vbat with a current source better matched to your LED optimal illumination current or use a regulated voltage supply operating in current limit mode. The current supply generates a voltage to make that current flow so is suitably switchable with an open drain. Just make sure the current source open loop voltage does not exceed 16V or you might burn out the chip when all segments are off (when there is no load to weigh the current supply voltage down)

traditional 74 logic based 7 segment decoders were based on parallel data and would be addressed much differently although biasing the LED diode would be similar. Those parallel 74 series circuits tended to be CMOS outputs and actually supplied the current but some were open drain or open collector. I didn't review all the datasheets that could apply.
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

yes the chip is a shift register, similar to the 595..shift register...but in a smaller package..

i guess i could regulate the display voltage in.. but i have not had too much luck with adjustable regulators..they seem too sensitive to adjustment.. but then again i have a wide vareity of the LM series.. 5,6,8,9,12,15 volts..
will have to give that a go and maybe a diode in series to fine adjust ?
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haklesup
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Re: looking for a led driver board

Post by haklesup »

I was thinking you could use something like this
http://www.ebay.com/itm/3W-100W-High-Po ... _SGTeyv0Hg

you can also find 5W if you look around. Just search on "LED Driver"
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

i'd prefer something in a low voltage input if possible..
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haklesup
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Re: looking for a led driver board

Post by haklesup »

http://www.icstation.com/icstation-cons ... -3255.html

This may be more toward your liking. In practice you would set the voltage adjust to the maximum voltage you want to allow (compliance voltage) and then adjust the current limit to the set point you need for the brightness you desire. This isn't the only DC-DC they have and if you want a display on it, that one cost only a few dollars more

http://www.icstation.com/current-voltag ... -2455.html


BYW, I love this website, it has thousands of assembled modules and unassembled kits. Only problem is they are shipped with the Chinese instructions and you need to download the translations from these pages. I just got 10 kits and modules delivered last week for my entertainment.
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

thanks for the links... that might be what i need,, looks great for all kinds of led driving..especially since it is all adjustable..
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Re: looking for a led driver board

Post by dyarker »

How many LEDs per segment? What color?
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

3 leds / seg. .red and 1 led for the Period.
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Re: looking for a led driver board

Post by dyarker »

2nd try. pressed submit before, and everything just d i s a p p e a r e d
Net access my end, not Nutvolts forum

3 LEDs in series more economical than parrallel, but takes higher than logic supply.

Red LEDs are probably 1.8V or 2.0V each. So 3 in series are 5.4V or 6V. To have some voltage for the current limiting resistors would call for a 9V, or more, supply. That would work for input to 5V regulator for logic. Lets take 12V as power in. And, 1.8V for your LEDs.

12V - 5.4V = 6.6V
18mA LED current because it is a bit less than 20mA (a common max for LEDs)
6.6V / 18mA = 366.6 Ohms, nearest standard value 365 Ohms
6.6V * 18mA = 0.1188W, too close to 0.125W (1/8W), so use 1/4W resistors.

For decimal point
12V - 1.8V = 10.2V
10.2V / 18mA = 566.6 Ohms, 560 or 562 Ohms are nearest standard value
10.2V * 18mA = 0.1836W, over 0.125W but well below 0.25W, so again a 1/4W resistor, only need one.

If your driver IC is open collector/open drain, that's it. Else, need a buffer schematic?

((now control A control C before hitting Submit)) :-)
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

i am not going to be driving them at full brightness, i just want it bright enough that i can't see it thru my eye lids..lol
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Re: looking for a led driver board

Post by dyarker »

Two ways -

1. Double the resistance to halve the brightness, a fixed amount of dimming.

2. In first post you said " ... i wan to make me a new display that is arduino controlled." Do PWM dimming in code in the microprocessor. For example (for "on" segments) 10mS on 0mS off is 100% brightness, 9mS on 1mS off is 90% brightness, and so on. ((and the resistors are calculated for 100% brightness, because the average current due to on/off ratio determines actual brightness.))
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dacflyer
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Re: looking for a led driver board

Post by dacflyer »

built one clock with giant 10" displays.. but i could not stand the PWM singing leds.. you could hear the leds whining..i thought i was hearing things, but a friend heard it also.. so i really don't wanna use PWN..
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