Joe Jansen wrote:

> Thanks for any suggestions!!!!!


Hi Joe,

I still have my E-mu Systems Drumulator drum machine (I love the '80s!). I
never bought the pad programmer for it, but here is some information that
might be useful to you regarding their piezo interface:



From E-mu Systems Drumulator Pad Programmer manual:
---------------------------------------------------

{
Pad Programmer - Theory of Operation - Revision of 2/27/84
The Pad Programmer consists of four independent trigger sensors with
appropriate
circuitry, with a common housing and power supply.
The power supply is a simple three terminal regulator +5V supply. The input
voltage is
between 8 and 25 VDC and the current requirements are small enough (around
40 mA
when an LED is firing, less quiescently) that heat sinking is not required.
The plug in
wall unit supplies nominally 10V DC, which is filtered and regulated.
The sensor is a piezo-electric crystal mounted in a housing designed to
transmit
pressure from a vertical strike by a drumstick, and attenuate vibrations
conducted by the
housing. This assembly is glued together and tested at the factory. Service
on these
assemblies will generally be by replacement, as repairs are difficult to
accomplish and
will frequently be unreliable.
The sensor produces a substantial voltage spike (10 to 100+ volts), which is
loaded by a
parallel capacitor and resistor, and rectified by a full wave bridge. The
resulting positive
voltage is attenuated and applied to one terminal of a comparator. The other
terminal of
the comparator is adjusted for the desired sensitivity threshold. The trim
range is set to
stay within the common mode range of the comparator. Positive feedback
around the
comparator is provided to minimize marginal switching. The comparator output
triggers
a one-shot which will both swallow any comparator oscillation or multiple
triggering, and
provide sufficient pulse width for the LED amplifier and for the output
trigger pulse. Both
of these signals are buffered from the one-shot output.
For information on adjusting the sensitivity trims, refer to the earlier
section.
}


Best regards,

Ken Pergola

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