n to n analog multiplexer - Page 1
Forum section: electronics / general

author: elektronicks
author_rank: Contributor
timestamp: June 24, 2012, 08:48:19 am
content: Hello Guys,I've been screwing my brains thinking about how to create a digital patcher for a modular synthesizer that will be ableto connect N analog signal outputs to M analog signal inputs via a uMC and some kind of interface.This seem to invole tons of switches or multiplexers but still the complexity is fairly large once you reach the maximumof channels per multiplexer.Somebody already did it but for 16 x 16 I/Ohttp://monopole.ph.qmw.ac.uk/~thomas/synthdiy/index.htmSo yes.. I have no ideea how the multiplexers can be interfaced each other to achieve:1. maximum number of "virtual paches" for low pin count2. an expandable address scheme to don't know.. achieve ease of uMC programming and future expansions3. analog signal + / - 15 v vppI've tryed with relays .. that will increase the part count considerably up to a point is no longer usable.Any thoughts on this problem ?

author: Psi
author_rank: Super Contributor
timestamp: June 24, 2012, 09:57:51 am
content: You could have a grid (rows=inputs cols=outputs) and use analog switch IC's.You can get those for audio switching that have 8 or so switches per chip.They come in many arrangements,eg8x 1in 1out4x 1in 3out2x 1in 4out1x 1in 8outYou set them with binary on the control pins, so easy to do from a micro.

author: elektronicks
author_rank: Contributor
timestamp: June 24, 2012, 10:32:12 am
content: yeah.. sure.. but suppose we have 250 inputs and 250 outputs. that is a matrix of 62500 switches)imagine all the people..I'm thinking of extracting selected outputs to some kind of "virtual busses" and then through a two layered model toroute them to the destination somehow.. the simple matrix ideea does not answer to the scalability thing, and neitherto addresing scheme.I would have something like this for addressing:bus[0..63]:[0..255]:[0..255] whereassigned bus / input line / outputline ..We also give toughts on some mechanical sollution but this is rather cumbersome.

author: Psi
author_rank: Super Contributor
timestamp: June 24, 2012, 11:08:53 am
content: hm.. that's a lot of connectionsYeah, some sort of modular design where you have stackable input and output modules.Each module could support say, 20 signal connections and handle maybe 5 concurrent connections to other modules.A input or output module would need 20x5=100 switches, or 13x switch ICs.You could have either separate output and input modules or a universal module that can do both on any connection.A universal module would be more complex as it would have to deal with routing within itself.Or another totally different idea, a DAC for each output channel and an ADC for each input channel. Then route the signals all digitally.You can get 8 channel DAC chips in DIP, i've used them before. So 3 chips could do 24 outputs.You would only be limited by the speed of the micro and how many concurrent channels it can keep up with.If the audio quality requires more than 8 bit DACs they may get expensive and it will slow down the routing.Ideally you want parallel ADC / DACs so you can copy the entire ADC port to the DAC port in one line of code.

author: elektronicks
author_rank: Contributor
timestamp: June 24, 2012, 12:29:39 pm
content: yeah.. i thought digital too.. but i'd like to keep the analog sound .. that;s the thing) why bother having a modular synth with the vco-s and stuff if somewhere signal gets 101010010101..

author: Hypernova
author_rank: Unknown
timestamp: June 24, 2012, 06:03:21 pm
content: Quote from: elektronicks on June 24, 2012, 12:29:39 pmOnce you get to a certain scale you simply won't have a choice. The size of the switch fabric for something beyond 32x32 (1024 links) is simply too big to wire by hand. For something like 256^2 DAC/ADC with FPGA or MCU is the only way to go unless you want a PCB the size of your door.

author: elektronicks
author_rank: Contributor
timestamp: June 25, 2012, 12:26:18 pm
content: check this out:http://www.analog.com/en/switchesmultiplexers/analog-crosspoint-switches/ad8113/products/product.html