More on Crosspoints.

[Paul Maddox]

Tony,
>
>    Can crosspoints wire two or more inputs to the same output?  I
> wouldn't think that very wise as they don't have a summation amp on each
> of the output lines!

yep, not a single one on the market does it...
Does no-one do this kind thing with chips any more?

>    I have been thinking about this sort of situation for a few weeks
> myself and I think what you really want to do is use an analog
> multiplexer and then run each of your input lines with a summation amp
> that has enough inputs as your matrix array.

yes... one solution that would work, agreed.

>    And in that setup, you'll want the lowest ON resistance as you can get
> (although most likely anything under 50 ohms will be adequate).

yep.... agreed, as low as possible and also aswell matched as possible.

>    Unfortunately this won't help in the chip count area, lots of chips
> (at least 36 for a 16x16 array (32 multiplexers and 4 quad op-amps)),

Haveing looked around a bit.. Ive ordered a few samples of the MAX335 chip.
Its an octal switch with inbuilt latchs and SPI interface. It'll handle full
scale swings within the supply rail limits which are +/-20v, so it'll sit
nicely with a +/- 15v supply.

I'll common all the outputs and drag these into an opamp. I'll put 10K
resistors on each input and take them to each of the 8 inputs. then use a
74hc138 to decode the CS line.
So I can use 8 max335's, 2 TL074's and one 74hc138.. 11 chips per 8by8
matrix which I should be able to fit (hopefully) on a single eurocard.
I actually want a 24by24 matrix, ok Im nuts but I do. This means 9 boards to
get what I want, this is better than my current solution which would've
needed 18 boards (useing 4066's).
So, I now need to find 9 of those 8by8 LED arrays for displaying the matrix
settings.

I would like to find some of these in a single chip though. as I want to use
these for a poly-synth and I dont really want a MONSTER sized rack. I plan
on usieng a touch screen for the poly version with TFT display.

Paul MADdox
_________________________________________________________
Vila: I've got this shocking pain right behind the eyes.
Avon: Have you considered amputation?

Modulus website;-
   Http://www.noxons.ision.co.uk
_________________________________________________________