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Arduino microdrum - HELP

ashleymosey

okay so iv started a project were im going to build my own electronic drum kit from the ground up and iv been searching for ways to build a drum module as to buy 1 is expensive and if I can make one then why not

 

so i did some research and the one that got my attention was the MicroDrum http://microdrum.altervista.org/blog/?doing_wp_cron=1486083012.4330480098724365234375

 

The MicroDrum is a shield/addon that you attach to the Arduino that with some code on the Arduino converts triggers from a piezo transducer to Midi so it can be understood by software like GarageBand or Addictive Drums that then basically enables me to use an Arduino plus the micro drum with a PC to produce the drum sounds and give me a working electronic drum kit 

 

Now the Microdrum's PCB is sold on the website but I'm on a budget and its cheaper to make my own and the maker of the Microdrum supply schematics found here: http://microdrum.altervista.org/blog/downloads/?doing_wp_cron=1486083519.0516369342803955078125 along with picture of the PCB but the Schematics are in PDF format so cannon be opened in something like easyeda for example and i tried to copy the schematics over to easyeda but tbh I'm very confused and do not understand the spider web that is happening in the schematics microdrum supplies and when i get the parts in easyeda and place them they look completely different to what's in the original schematics but if i look at the data sheets for each part they match easyeda but not microdrums schematics so im having difficulty copying the data over my knowledge of electronics is enough to just get me by and i think this a little advance for me im hoping someone will be kind enough to help me out il put any usefull links below

 

Parts List: http://microdrum.altervista.org/wiki/index.php?title=Parts_List

Assembly Guide for if you buy the PCB (has useful images) http://microdrum.altervista.org/wiki/index.php?title=Building_with_the_PCBs

Micro Drum Wiki Main Page: http://microdrum.altervista.org/wiki/index.php?title=Main_Page

Micro Drum Schematics: http://microdrum.altervista.org/blog/schematics/?doing_wp_cron=1486084085.1847140789031982421875

 

 

Here is what iv managed to sort out so far but i have no idea if this is correct iv only included 3 Multiplexers because that give me enough ports to connect a standard drumkit and have a spare

image

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  • in reply to ashleymosey

    All inputs on the arduino MCU are have built-in protection diodes which clamp the inputs from exceeding the power supplies. It is not clear how much energy they can take but it would seem they survive well enough for other people.

    The Piezo disk can generate over 100 volts. The mux chip has an impedance of less than 70 ohms which would limit the clamping current to about 1.4 A. Fortunately the piezo disks only have about 1nf of capacitance so the current is not high for long. The arduino MCU and the mux chip are both only rated to take 0.5 Volts beyond the power supply rails. The mux clamping diodes can take a max of 20 mA , but as these are connected to the piezo disk with no current limiting resistor, it is only stray capacitance that would help to absorb the current . The 20 mA clamp limit is typical, so the MCU may be similar. Which means, on paper the inputs should not be directly subjected to a piezo disk. It would take a more careful analysis or measurement to discover how close these disks are to over-stressing the inputs but definitely stress the inputs - however if it works.....

    I would at least add footprints for protection diodes on the PCB even if you don't populate them with parts - just in case they are needed.

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