Archive of the former Yahoo!Groups mailing list: MOTM

This circuit outputs a trigger if the input voltage varies more than a
certain amount over a period of time. Although it was designed to generate
trigger outs from a UEG running in LOOP ONLY mode, it in no way modifies
the UEG. Consider it a separate module. Thanks to Moe and Tony Allgood
and for their input.

It consists of a differentiator, two comparators, an OR gate, and a pulse
stretcher. In ascii, it looks like this:



+15V
|
/
\ 100K
/
| 10K |\
+----------------------/\/\--(-)| \ 1N4148
| 10K | >---->|--+
/ +--/\/\--(+)| / |
47 \ 1K 100nF | |/ |
/ IN-/\/\--| |--+--+ | 20K
+--+ | | TL072 +---/\/\--> A
| / \ | |
= \ 47 / | |
/ 20K \ | 10K |\ |
| | +--/\/\--(-)| \ 1N4148 |
| = 10K | >---->|--+
+----------------------/\/\--(+)| /
| |/
|
\ +15V-------------------------+-------+------------+
/ 100K | | | |
\ / ____________ | / R1 |
| 20K \ | | | \ 475K |
-15V / +----| 1 8 |---+ Vcc / |
| = | | | |
+------+---------| 2 NE555 7 |-----------+ C1 |
| | | | .01uF |
| +---------| 3 6 |-----------+---| |--+ |
/ | | | .01uF = |
|/ c | +--| 4 5 |---| |--+ |
A >----b-| NPN | | | | = |
|\ e | | ------------ |
| | +----------------------------------------+
| /
= \ 1K
/
+-------> OUT
\
/ 1K
\
|
=



Each op-amp is half of a TL072 run off the -15V/+15V supply. The 555 timer
is single sided. The three 10uF bypass caps are not shown.

The NPN is a generic switching transistor -- it was unmarked. All
resistors are 1% 1/4W. While 1% resistors probably are not necessary, it's
what I already had on hand. So it was less expensive to use them than go
buy new 5% resistors.

The input is differentiated by the 100nF cap and 20K resistor. It's output
goes to each comparator. I originally used 10 Ohm resistors, but I found
it was too sensitive. The output of the UEG wavers a bit under certain
conditions -- being cold, being set between two values, and when driving
long cables. With the 47 Ohm resistors, the circuit ignores changes of
less than 10mV or 20 cents in pitch. Increasing their value decreases the
sensitivity of the circuit. I see no reason why they could not be replaced
with pots to make the sensitivity adjustable.

When the output of the comparators goes high, the NPN transistor turns on,
bringing the trigger input low. This fires the 555.

The length of the output pulse is determined by R1 and C1 (t = 1.1RC). On
paper, this gives a pulse of 5.2mS. Increasing the values of either R1 or
C1 will increase the length of the pulse. The two 1K resistors divide the
voltage of the pulse in half, resulting in about 6.5V.

I built this thing and it works.

Monkey Tested.
Monkey Approved.



DISCLAIMER: I am not EE. I do not speak for Synthesis Technology,
Encore Electronics, or anyone else, nor should I.
Any possible information is provided purely for
entertainment purposes. I take no responsibility for
the veracity of any claims. If attempting to use
this circuit results in you destroying your modular,
that's your problem.