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click on the schematic for a larger version.
<a href="http://casperelectronics.com/images/finishedpieces/benjolin/BenjAREnvGen2.jpg"><img src="http://casperelectronics.com/images/finishedpieces/benjolin/BenjAREnvGen2.jpg" width="400" height="250" alt="" title=""  /></a>
By no means is this a necessary addition to the benjolin but its one I've had some fun playing with and decided to add to my <a href="http://casperelectronics.com/finished-pieces/benjolin/modular-benjolin/">Modular Benjolin</a> design. This circuit is a dual Attack/Release envelope generator. The AR is especially useful when combined with the modular<a href="http://casperelectronics.com/rungle-mods/"> rungle bit output mod</a>.   This is a very simple design and is easy to build and use. It is also relatively easy to modify for other applications. You could definitely get by with one but its such a low part count and required just one IC so I decided to build two.
Operation:
The A/R has 3 stages:
1.	Comparator/input buffer
2.	Envelope shaper
3.	Output offset/LED driver
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COMPARATOR:
R5 and R6 creates a voltage divider that sets your threshold voltage which has been set at around 2.5volts. Any incoming voltage above 2.5 volts will trigger the comparator and set the output high (which is 9 volts for this circuit).  
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ENVELOPE SHAPER:
This is a simple RC slope generator. The rate of attack and decay are determined by the two potentiometers and the capacitor (C1 for A/R1 and C2 for A/R2). R7 and R8 act as peak limiters. 
Note that the AR curve is non linear. A linear curve could be achieved with a more complex circuit but in most applications the RC curve is just fine.
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OUTPUT OFFSET/LED DRIVER:
The voltage coming out of the op amps (pin 1 and 14) is an envelope that swings between the power rails (+9VDC and -9VDC). In actuality it will swing just below +9VDC and above –9VDC. If you want a bipolar envelope then leave out the offset. I want the base voltage to be exactly 0 volts so I installed a trim pot to the positive power supply. I use this to pull up the negative swing of the envelope until it is exactly 0 volts. It will take some fine adjustment. An oscilloscope will make it a lot easier but isn’t totally necessary. One way to test without a scope is to plug the output of the AR generator into the CV input of a VCO (like one of the ones on the benjolin). Make sure the AR is not being triggered. Unplug the connection to the VCO CV in and make a note of the pitch. Plug it back in and adjust the offset pot until the pitch is the same whether it is plugged in or not.    
