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#882965 - 10/24/05 06:29 PM Making a MIDI drum
beatpantz
Member


Registered: 10/24/05
Posts: 1

Offline
Hello all,

Was wondering if anyone could help me, or assist me in the right direction with regards to making a MIDI drum trigger.... I shall elaborate:

my aim is to create an audible sound from the triggering of a piezo transducer, basically a scalled down version of a midi drum.

my friend tells me the process will be something like this:

impulse detected (piezo is hit)
impulse converted to digital via ADC
threshold breached
note on
velocity picked up through 7 bit ADC
eprom triggered
sound out (via headphone)

I need to build a simple circuit this week were the piezo is hit and a sound which is stored on an eprom comes out of a speaker. I would also like the sound to be velocity sensitive.

Could anyone advise?

Thanks

Marc
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#882966 - 11/11/05 12:21 PM Re: Making a MIDI drum
philbo_Tangent
Platinum Member


Registered: 10/08/00
Posts: 1175
Loc: Iowa

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1) It'd be easier, faster and cheaper to buy a drum machine with several trigger inputs that would generate both sound and MIDI output from your piezo inputs.

2) If you are determined to do-it-yourself:

If you just want sound output, you don't need MIDI.

If you want MIDI output (to trigger drum machines, samplers or other synths), it'll take more than an EPROM. Each MIDI message consists of a few bytes, which are output serially at about 38 Kbits/sec. Typically, it's something like this:
Byte# Meaning
1 Note-On
2 Note Number (1-127)
3 Velocity
(Then, after the note duration, a second message):
4 Note-Off
5 Note Number (same number as previous)
6 Velocity

This would happen for EACH drum hit.
To transmit MIDI, the simplest way would be to program a PIC processor chip to generate the data bytes and serially output them to a MIDI output. Unless there are MIDI chipsets out there somewhere (I've never heard of any, but I never looked for them either..)

You probably don't need the first ADC. A simple comparator would work as well at a fraction of the cost. The unused input of each comparator can be fed a DC voltage to set the threshold level. Now, if you need to be able to set the threshold digitally, you *could* drive each comparator threshold input from a DAC. But if not, a simple knob for each channel would be much simpler. And easier to use.
_________________________
Phil
Tangent Studios
http://artists.iuma.com/IUMA/Bands/Tangent2/

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#882967 - 12/05/05 10:44 AM Re: Making a MIDI drum
techristian
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Registered: 11/01/01
Posts: 1244
Loc: Windsor,,CANADA

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This is like beating your head against the wall. This would definitely be more than just a one week project because..............

my friend tells me the process will be something like this:

impulse detected (piezo is hit)
impulse converted to digital via ADC
threshold breached

right in this area you must write SOFTWARE to determine NOTEON and NOTEOFF. Then it must convert to serial 31,250 data stream and send to MIDI OUT port...not a one week project.


note on
velocity picked up through 7 bit ADC
eprom triggered
sound out (via headphone)


Dan

http://teachmedrums.com
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A new subscriber section now at teachmedrums.com!!
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