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 Forum index » DIY Hardware and Software » Thomas Henry designs
Adding a LED drivers to TH AD Enveloppe Generator
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Dozemuisc



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PostPosted: Thu Jul 11, 2019 8:42 am    Post subject: Adding a LED drivers to TH AD Enveloppe Generator Reply with quote  Mark this post and the followings unread

Hello!

I would like to add two leds to this design, (one that light up during the attack and one that light's up during decay).

We don't have much space left on the PCB so we would like someting with as few components as possible.

Would this design work?

Thank you very much!


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Grumble



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PostPosted: Thu Jul 11, 2019 9:45 am    Post subject: Reply with quote  Mark this post and the followings unread

The attack led “might” work when placed before the diode directly to pin 3.
Since pin 7 is an open collector (it can only sink, not source) this will not work, worse: the whole circuit will stop working because the timing capacitor will not charge due to the low impedance formed by the R+LED
You could try to place this led + resistor from vcc to pin 7, with the cathode towards pin 7.

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Dozemuisc



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PostPosted: Sat Jul 13, 2019 5:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Allright thank you very much I'll try to prototype that!
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PHOBoS



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PostPosted: Sat Jul 13, 2019 9:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Grumble wrote:
You could try to place this led + resistor from vcc to pin 7, with the cathode towards pin 7.

I think the capacitor would get charged through the LED that way. I am also pretty sure the LED would stay on until the next attack.
I don't know how much space you have left but using a dual opamp to create 2 comparators should work. You don't realy need it for
the Attack LED but it doesn't take up any more space than a single opamp.

btw the resistor vaues for the LEDs is rather low, at least for modern LEDs.

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Grumble



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PostPosted: Sat Jul 13, 2019 11:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
I am also pretty sure the LED would stay on until the next attack.

You are right, sorry about that Embarassed

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richardc64



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PostPosted: Sat Jul 13, 2019 12:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Add a diode and move Decay to pin 3. That'll free Discharge to sink the Decay LED.

PHOBoS wrote:
btw the resistor vaues for the LEDs is rather low, at least for modern LEDs.


@ 5volts I needed 33k to make ultra-bright LEDs merely bright, so at 15V...


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PHOBoS



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PostPosted: Sat Jul 13, 2019 1:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Add a diode and move Decay to pin 3. That'll free Discharge to sink the Decay LED.

That would still leave the LED on until the next attack cycle but otherwise it should work.
Not sure why Thomas Henry used pin 7, makes me wonder if the diode on pin 3 prevents it from going completely to GND.

Quote:
@ 5volts I needed 33k to make ultra-bright LEDs merely bright, so at 15V...

It's ridiculous isn't it. I've used 100K myself for some blue LEDs, but I think that was on 12V.

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PostPosted: Sat Jul 13, 2019 5:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
It's ridiculous isn't it. I've used 100K myself for some blue LEDs, but I think that was on 12V.


And blue LEDs are just evil.

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Dozemuisc



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PostPosted: Wed Jul 17, 2019 7:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow thanks I learned a lot of stuff.

Mainly that it's too complicated to do. I'll just stick with one LED.

It should work with this design :


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PHOBoS



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PostPosted: Fri Jul 19, 2019 2:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'd add a resistor in series and then connect it straight to pin 6.
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