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Old 6th September 2008, 08:50 AM   #1
onform is offline onform  England
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Talking can anyone help with CCS

Hello

I need help building a CCS to power 1-24 Led's which will be used to show the position of my volume pot.

using two pnp transitors has been mentioned but i'm not sure how this works or how to implement it!

Any help would be appreciated.

these are the led's i will probably use: Hyper blue diffused led's
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Old 6th September 2008, 09:57 AM   #2
onform is offline onform  England
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Default please

any help?
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Old 6th September 2008, 10:00 AM   #3
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There's a few different ways, Google and 10 minutes will show you...

Although I don't think you need a CCS, you need a bargraph driving chip or bunch of comparators. Otherwise how are you going to make them come on in sequence? Also you need a 3 or more gang pot (2 tracks for left & right, 1 for the LEDs) if you are trying to do this all analogue.
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Old 6th September 2008, 10:07 AM   #4
lineup is offline lineup  Sweden
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the problem we fact here is
that if
you feed the transistor that will trigger LED to light
at one certain position
from the audio signal = the stepped attenuator resistor divider
then you will have

1. one construction design problem
2. possibly some distortion caused by the current needed to trigger the transistor BASE


solution can be.

use one 2 x 24 position stepped attenuator
where one set of those 24 positions are NOT for SIGNAL
but only for trigger one of 24 transistors

But really,
i would not go for any LEDs to show volume level
just use one normal scale with one mark for each position
as you turn the knob
this way, you can use your 2x24 stepped attenuator
for BOTH left and RIGHT channel


Can you tell a bit more about what gear you have, so far.

Regards
Lineup
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Old 6th September 2008, 11:41 AM   #5
onform is offline onform  England
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Default here goes

Ok I want to achieve a volume indicator using blue Led's, the first step will iluminate the first led the second will illuminate the first and second and so on until all are lit.

I intend to use a two channel 24 way stepped attenuator for left right signals which i was planning to incorparate into the amp anyway.

Then I plan on making my own pcb with a 24 way switch incorparated, this will be mounted on the rear of the front panel on the same shaft as the attenuator this will feed the power to the led's the wiper will be connected to the supply. the Led's will be wired in series so i can switch between the led's lighting them in sequence. hopefully

My problem is with the supply and values of said supply. now i know there are easier ways of doing this but where would be the fun in that...lol

I have been doing some research on the net to try and teach myself but i'm not getting very far! my trouble is I learn by doing something so if you could help me i will grasp it as im doing it.

If that makes sense.

Matt
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Old 6th September 2008, 02:28 PM   #6
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Neat idea but it's going to need a supply voltage of 24x Vf yielding 74.4 volts even before the CCS headroom is taken into account. Also maybe the knob will be a bit stiff with two lots of switches on it?

Anyway I have a good little circuit for you here.

Click the image to open in full size.

R3 is the load i.e. your string of LEDs. As shown with LEDs having Vf=2.1 used for the CCS it's running at 5mA. If you use your blue LEDs having different Vf then you will need to change the 560 ohm resistors R1 and R2. The transistors shown will be fine for the application but small heatsinks are needed. The supply voltage should be 82-100 volts.
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Old 6th September 2008, 04:09 PM   #7
CBS240 is offline CBS240  United States
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Hi Matt

Is your intent to indicate the level of gain or the level of signal? If you are trying to show the signal level, a LM3915 may be a simple solution. This chip uses a logrithmic scale. The LM3914 is a the linear version. IMO, easier than building a discrete version and they can be strung together for more led's.
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Old 6th September 2008, 05:34 PM   #8
onform is offline onform  England
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Quote:
Originally posted by CBS240


Is your intent to indicate the level of gain or the level of signal? If you are trying to show the signal level, a
it is mainly a visual thing just to show which position of the attenuator.

richie00boy

That does look good, what is the purpose of the led's in the ccs?? Iwas thinking along very similar lines but no led's.. what do you think of this?

Click the image to open in full size.
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Old 6th September 2008, 05:41 PM   #9
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Your base current will be dependant on your supply voltage in that circuit. The led sets up a constant voltage to be used as a current mirror.

richie00boy's CCS works, but needs a 1M resistor tying the bases together to ensure smooth startup.
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Old 6th September 2008, 05:45 PM   #10
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Default a very simple idea will be

to forget using all these complicated stuff and simply make a mechanical construction or any other way to run parallel with your volume control another pot

in case your volume control will be a step switch then simply you need to have a step switch with one partition more (one partition to be used as volume control and then another one to be used as the led control)

then you can use LM3914 or uaa 2022 or any other led driver but hooked up as a volt meter ..... so in step number one you have voltage enough to drive the first led and then 10 turn trimmers or very good calculations and presision resistors to go to next step and so on and on till the last step .....

the same will apply if you have a potentiometer but there calibrating the led potentiometer to follow the volume will be not an easy task

regards sakis
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