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Satindas
Joined: Mar 26, 2011 Posts: 39 Location: uk
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Posted: Thu Feb 09, 2012 3:15 pm Post subject:
Clock divider Led resistors |
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Hi Yves,
Could you tell me which resistors to change for the Clock Divider LED's.
My blue led is soooo bright.
Many thanks |
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ungleichklang

Joined: Dec 03, 2011 Posts: 63 Location: East-Belgium
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Satindas
Joined: Mar 26, 2011 Posts: 39 Location: uk
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Posted: Fri Feb 10, 2012 3:17 pm Post subject:
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| ungleichklang wrote: | I haven't build it, but as far as I can see from the shematics,
the devider has 3 LEDs
they are connected to (R12, R24, R36) 220R resistors.
I think (I am pretty shure) you have to change those  |
Thanks ungleichklang. I was suspecting those resistors but not sure if it could also be down to 13, 25 & 37. Changing either of these two groups would seem to alter the potential divider across the output..  |
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Mongo1
Joined: Aug 11, 2011 Posts: 393 Location: Raleigh NC
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Posted: Fri Feb 10, 2012 8:39 pm Post subject:
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| Quote: | | I was suspecting those resistors but not sure if it could also be down to 13, 25 & 37. Changing either of these two groups would seem to alter the potential divider across the output.. |
Yes- you're exactly right.
Since you're trying to use those #$S# blue LEDs, it's not unusual to have to use a 10K resistor with them. That will mess things up in this case.
Here's what I think you could try (do it on one of the circuits first to see if this works)
1) Connect the cathode of the blue LED to a 10K resistor to ground.
2) Connect the top side of R12 directly to the emitter of the transistor (pin 7 on the schematic). You should probably increase the size of that resistor until the output level is at 10V (if you have the zener diode in place, this won't matter).
I think that should do the trick. Alternately you could change R12 to 10K, and do some math to work out a new value for R13 that would restore the output level to 10V.
OR you could just use regular LEDs
Gary |
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Satindas
Joined: Mar 26, 2011 Posts: 39 Location: uk
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Posted: Sat Feb 11, 2012 1:36 am Post subject:
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Thanks Gary. That all makes sense. I think I'll do a quick simulation based on your suggestions (my electronics math is rubbish). Why did I choose blue? For quicker id. I have a different colour led for each output; red, yellow and bue. I'd settle for red,yellow and green but I'm red/green colour blind.  |
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Satindas
Joined: Mar 26, 2011 Posts: 39 Location: uk
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Posted: Sat Feb 11, 2012 2:11 am Post subject:
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so this is how it looks...
Replace R36 with 470R connected to emitter of Q9 (maintains 10V at output)
Blue led to ground via 3K3 resistor ( 3.54 mA through led = half of original current)
Doing it the other way; subbing a 1K for R36 and 3K for R37 gives 9.48V out and 3.16mA through the led. (good enough for jazz!)
So...Gary I like your idea of a separate ground connection for the led. At least that way if the led fails I still have a clock output.
Gary... Now I can remove my shades |
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Mongo1
Joined: Aug 11, 2011 Posts: 393 Location: Raleigh NC
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Posted: Sat Feb 11, 2012 7:01 am Post subject:
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I'm glad I could help.
BTW - I have one of those modules sitting on my table right now. Still waiting to get built!
I like the idea of using different LED colors for each channel. I think I might do that. Thanks for the idea!
Gary |
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