[sdiy] Doepfer E510 Keyboard Scanner

[Steve Lenham]

On 06/02/2019 03:21, Miles Stevens wrote:

> Poking around the web looking for a polyphonic keyboard scanner to MIDI 
> solution and stumbled on the Doepfer E510 IC through an Elektor project 
> that utilised it. Seems quite old now but wondering if anyone had 
> experience with it?

Ah, a blast from the past!

In the UK, Maplin used to sell the E510 in their shops and catalogue. It 
was very expensive for a single IC but did something that was otherwise 
much harder to do in those days (late 80s/early 90s).

Yes, they kept their package pin-count down by reading only a single 
pair of switch contacts at a time and requiring that the address be 
externally decoded. But it is hardly rocket science to interface it to a 
standard keybed - in fact, you could argue that by not committing to any 
particular matrix arrangement, it is more flexible.

Want an example of how it can be done? Check out the article on p40 of 
the August 1992 edition of ETI magazine written by...ahem...me:

https://www.americanradiohistory.com/Archive-Electronics-Today/90s/Electronics-Today-1992-08.pdf

I remember sitting in the university library drawing the PCB layout by 
hand on acetate - happy days :-)

Please note that there are a couple of minor errors in that article. 
First, each keyboard J-wire should have an isolating diode in series 
with it, pointing towards the row drive line. I forgot to include them 
in the schematic because I was using surplus keyboard mechanisms that 
already had them present.

Secondly, the 1Meg pull-up/down resistors on the switch read lines are 
too high and should be lower for reliable operation, particularly of the 
last key in the matrix.

FWIW, I built a six-octave keyboard by splicing together two surplus 
three-octave mechanisms that were originally peripherals for the 
Sinclair Spectrum. They only had SPST switch contacts, so I added new 
SPDT busbars but kept the original J-wires.

Hope this is of some interest - thanks for the memories!

Steve L.
Benden Sound Technology