Yamaha DTXpress/DTXplorer/DTXtreme

I have a new circuit diagram that I would like to post here for 
comments. It is an IC based piezo-switch adapter, with much fewer parts 
than the DTXpander. I am not sure how to add the JPG file in the Files 
section. Does it also need to be approved? Thanks.

--- In DTXpress@yahoogroups.com, "bznx9c" <bznx9c@...> wrote:
>
> I have a new circuit diagram that I would like to post here for 
> comments. It is an IC based piezo-switch adapter, with much fewer 
parts 
> than the DTXpander. I am not sure how to add the JPG file in the 
Files 
> section. Does it also need to be approved? Thanks.


Sounds interesting. Technically minded members will want to see it, as 
will Keith when he returns later this month. No permission necessary 
to add the file. Just go to the files section (see menu box to left) 
and click on "add file" at bottom of page.

Ed

Here it is, please find the PiezoSwitch.jpg in the Files section. The 
only parts needed to make this circuit are the LM339 comparator IC and 
a few Schottky diodes. There are no resisters to adjust or transistors 
to match, and is very reliable. The only catch is, it needs a power 
supply. I am using a 5 volt adapter from a cellphone charger. It is 
possible to use the 12v power from the DTXpress if you want to further 
reduce the parts count. Just make a Y-splitter for the 12v DC power 
cord.

The beauty of this circuit is its simplicity and low cost - a LM339 
($1.29 from RadioShack) and 8 diodes will take care of 4 stereo inputs. 

I thank Keith for his original DTXpress circuit for the inspiration.

--- In DTXpress@yahoogroups.com, "bznx9c" <bznx9c@...> wrote:
>
> Here it is, please find the PiezoSwitch.jpg in the Files section. 

You might want to make the threshold adjustable with a potentiometer
instead of fixed resistors.  Also, you might want to put a resistor in
series with the inverting input (maybe 100k) to protect the comparator
input.  You can easily get 15V out of the piezos which could blow up
the comparator if you are running it on less than that.

Your circuit will work fine, and be more sensitive than the one I have
been proposing.  However, I tried to get away from power supplies for
a few reasons - risks of liabilities blowing up other people's
modules, cost, regulatory issues, and supplying it to different
countries.  I did build a complex system with gain in the rim switch
side as well to overcome the DTXpress module's lack of rim sensitivity
- see "DTXpander E.pdf" in the files section.

As it is, I will probably have to stop selling ready built modules to
people due to WEEE regulations.  

Keith.