[sdiy] Hammond Aurora Keybeds

[rburnett at richieburnett.co.uk]

You can also do whatever flavour of switch de-bouncing that you want in 
software, if the key contacts are a bit old and scratchy!

-Richie,



On 2025-05-16 03:54, Ben Bradley via Synth-diy wrote:
> "Each key closes a switch to a common bus."
> 
> There's a couple things you need to make a "true analog" mono
> keyboard. First is a constant current source to drive the resistor
> divider, so that when more than one key is pressed the voltage remains
> that of the lowest or highest key (unless you WANT a weird off-pitch
> note effect when pressing more than one key). The other is  a separate
> switch at every key that closes AFTER the key that gives the pitch
> voltage as the key goes down, so that the proper voltage is sampled
> and kept when the key is released. This is also the gate/trigger
> output. Presuming there are several common busses, you need to bend
> the contacts on each key to make sure these close in proper sequence.
> 
> I don't see a problem of being off-pitch with a resistive divider, as
> 1 percent resistors are cheap thesedays, whereas 1970s keyboards may
> have used 5, 10 or even 20 percent tolerance resistors.
> 
> But still, I'd as soon make a digital circuit to scan/read all the
> separate inputs, one for each key, scan it into a buffer with a
> microcontroller and do the highest/lowest/latest keydown logic in
> software and the usual DAC for control voltage output.
> 
> On Wed, 14 May 2025 at 22:54, drheqx via Synth-diy
> <synth-diy at synth-diy.org> wrote:
>> 
>> Hi all,
>> 
>> I have the keybeds and draw bars etc. from a Hammond Aurora organ.
>> 
>> These are not matrix type keybeds. Each key closes a switch to a 
>> common bus.
>> 
>> Is this a good time for me to consider doing a volt
>> /octave keyboard controller?
>> 
>> I definitely don't want to midify these. That would be a waste.   I 
>> was considering building a voice per key synth because i love these 
>> key beds and it would be so unique, but I'm short on time like so many 
>> of us.
>> 
>> Anyone know of a good kit to make a 1v/ oct controller, maybe with 
>> some added features.
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