(2) DIY Digital Scanning Keyboard (Cor Blimey!)

[Clive Jones]

Hi Peter

>Hi Clive !

>>1 - Build a clock circuit around 500khz, this should scan each key on a   
    

>>64 (yep, I know it should be 61 but 8x8 - yes?) keyboard every 7.8Khz,   
    

>>plenty of time! The keyboard scan will occur every *other* event, the   
    

>>non-keyboard scan event time or "blanking" period will be used for the   
    

>>interface device to access the scan results from RAM e.g scan keyboard,   
    

>>rest (one full keyboard scan event time - read results), scan
>>keyboard.....

>I don4t understand why you don4t want to use an microcontroller (this
>controller can generate midi-note-controls, too, so controlling   
additional
>equipment is possible) - but ok.

It's just a project idea - less uP overhead and a data word output was my   
main thinking behind this.

>But with this design you will get problems. Think of pressing three keys   
at
>the same time: If you press f.e. the keys 1/4, 4/4 and 4/6 you get an
>automatic connection of the scan lines at point 1/6 (and so a "pressed   
key").

>But you can avoid this by adding a diode to each matrix crosspoint.   
That4s a
>common solution an you can find it in most keyboards (Korg Polysix and   
also
>in the little casio keyboards !).

Yep - I totally agree with you here, I assumed that most DIY'ers would   
know that diodes would have to be installed (read *matrix*) to keep the   
matrix pure. All matrix's are constructed  this way - synth keyboards or   
numeric keypads, it universal.

Have a nice day

Clive

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/<c.jones at sni.co.uk> / ...and on the 8th day
/01344 850213 Work   / God made Synthesizers
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