[sdiy] ADSR Question

[Scott Gravenhorst]

Oren Leavitt <oleavitt at ix.netcom.com> wrote:
>Hmmm...Maybe you need to set the maximum voltage going to the RC circuit 
>to a point just above that 1/2 Vdd level or use a comparator between the 
>RC and the 4069.

What I have is that the integration voltage is buffered with an opamp
follower, then thru a voltage divider so that the cap has to reach 6 volts
before the CMOS gate shows a state change.  (my Vdd is 8 volts, so this is
already well above the 1/2 Vdd point).  So I can get a curved attack, I
just didn't know if there was any standard (or at least, just what most
people do) for an ADSR using an RC timing circuit.  I noticed that without
the resistor divider, the trip point is 1/2 Vdd and that produces a rather
spikey attack, which lacks a punchiness that is there when the attack is
an obvious curve.  I probably would have used a comparator to do this, but
one of the things I wanted for this ADSR is low parts count.  At present,
it's just a 4069, TL072 and some diodes.

>
>Scott Gravenhorst wrote:
>
>>I have played with several designs for ADSRs.  My question
>>regards the attack curve.  In my lastest design, I used a
>>4069UB to make all of the logic.  Because I use a gate as a
>>threshhold detector, the attack portion ends when the
>>integration cap reaches 1/2 Vdd.  This gives a fairly
>>straight line for the attack curve.  I tried playing divider
>>games to get it detect at a higher voltage, but the circuit
>>became erratic when I pushed this too far.  I believe I was
>>able to get it to work reliably up to about 2/3 Vdd where it
>>looks pretty nice and rounded.
>>
>>Is there a standard threshhold that is used in most ADSRs? 
>>If so, what is it?
>>
>>=========================================================  
>>- Hydrogen is pointless without solar.
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>>
>>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>>-- Linux Rex         | RedWebMail by RedStarWare
>>-- FatMan: home1.gte.net/res0658s/FatMan/
>>-- NonFatMan: home1.gte.net/res0658s/electronics/
>>
>>
>>  
>>
>
>-- 
>Oren Leavitt
>oleavitt at ix.netcom.com
>619-579-5379
>http://www.betternutrition.healingamerica.com
>http://oren.profitmatic.com
>
>

=========================================================  
- Hydrogen is pointless without solar.
- That which gets rewarded, gets done.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- Governments do nothing well, save collect taxes.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.gte.net/res0658s/FatMan/
-- NonFatMan: home1.gte.net/res0658s/electronics/