Audio / Video source switching IC options? - Page 1
Forum section: electronics / projects

author: mkiijam
author_rank: Regular Contributor
timestamp: January 24, 2023, 05:57:19 am
content: Simple idea and it has been done a thousand times, but I find myself not being able to find a clear answer.Say for instance the INPUT buttons on a Home Stereo Receiver. "CD" "RADIO" "PHONO" etc. You push one switch and the systems selects it and deselects the previous choice. BTW, I'm not even sure what to call this function.Now, is there a chip or circuit (IC) that is the grand-daddy of them all for this function? I have seen it done Multiplexors, Decade counters, MCU, and of course mechanically with interlocking switches. I even dreamed up a system with latching relays and diodes, but... ISN'T there an existing off the shelf "INPUT SWITCHING IC" that does NOT require data and clock? Like an analog switch or something? If not, is the 4017 circuits really the best way to do it???

author: Terry Bites
author_rank: Super Contributor
timestamp: January 24, 2023, 08:38:49 am
content: Answer, I very much doubt it. Very much. What market would there be?A ring counter is probably the easiest (least parts) to implement.I'd call it a tristable.Here's a fun thing- the RCs are debounce.

author: Someone
author_rank: Super Contributor
timestamp: January 24, 2023, 11:21:44 am
content: Quote from: Terry Bites on January 24, 2023, 08:38:49 amUgly having to use RC in feedback!Quote from: mkiijam on January 24, 2023, 05:57:19 am"radio button" is the UI term, but there isn't a chip as volume production uses either a mechanical switch or jams all that into the firmware. Has been visited on here with some hardware solutions:https://www.eevblog.com/forum/projects/discrete-logic-design-vs-a-super-cheap-micro/

author: Ian.M
author_rank: Super Contributor
timestamp: January 24, 2023, 12:01:53 pm
content: Also seehttps://www.eevblog.com/forum/projects/selector-switch-using-push-buttons-(e-g-like-source-selection-on-an-hifi-amp)/I suspect the CD4028 + feedback resistors was a popular choice 'back in the day'

author: paulca
author_rank: Super Contributor
timestamp: January 24, 2023, 01:25:31 pm
content: I've used some H74 transceiver chips with the clock pin pulled low as passthrough level convertors.This is not an application mentioned in the datasheet, but it works.I wonder if the H74 series multiplexers will also "freeze" in passthrough with the right bit of torture and cajoling.On second thoughts... they will, clock or no clock all be based on logic levels.

author: mkiijam
author_rank: Regular Contributor
timestamp: January 24, 2023, 07:21:03 pm
content: Here is the electro / mechanical version, just to be clear.

author: Benta
author_rank: Super Contributor
timestamp: January 24, 2023, 11:08:33 pm
content: This would be my way of doing it (inputs need pull-down resistors for the switches and a reset circuit has to be added to the FFs):

author: cantata.tech
author_rank: Regular Contributor
timestamp: January 25, 2023, 02:18:39 pm
content: Quote from: Terry Bites on January 24, 2023, 08:38:49 amJapan was very successful at turning out millions of them, primarily designed by Sanyo and made billions of dollars making audio systems.These IC's already exist.Actually, on some of them they do nothing. All the wires seem internally bridged. The controller just carefully stops one (powers it down) before starting another (powers it up).Hate to say smoke and mirrors, but I don't know the technical words for any other way to describe them.

author: mkiijam
author_rank: Regular Contributor
timestamp: January 25, 2023, 05:14:04 pm
content: Quote from: cantata.tech on January 25, 2023, 02:18:39 pmDo you know of a part number?

author: coromonadalix
author_rank: Super Contributor
timestamp: January 25, 2023, 05:30:42 pm
content: https://www.analog.com/media/en/news-marketing-collateral/product-selection-guide/choosing_switches_or_muxes.pdfhttps://www.analog.com/media/en/technical-documentation/data-sheets/ADG798.pdfhttps://www.ti.com/lit/ds/symlink/lmh6574.pdf?ts=1674667794802&ref_url=https%253A%252F%252Fwww.google.com%252Fhttps://www.analog.com/en/products/dg1207.html#product-overview

author: mkiijam
author_rank: Regular Contributor
timestamp: January 25, 2023, 05:48:11 pm
content: I appreciate the links. I'm reading through these.Quick question in case you know, Do these chips allow for momentary switches to be used to latch the output until another is pressed? If not, then they of no use to me.

author: Benta
author_rank: Super Contributor
timestamp: January 25, 2023, 06:01:10 pm
content: Quote from: mkiijam on January 25, 2023, 05:48:11 pmNo. They're simply analog switches, like the 4051 in the circuit I posted.

author: cantata.tech
author_rank: Regular Contributor
timestamp: January 26, 2023, 03:11:34 pm
content: Quote from: mkiijam on January 25, 2023, 05:14:04 pmIt wouldn't be just one part that you need unless you'relooking for the whole unit:https://www.jaycar.com.au/search?text=video+selectorFor something more DIY, here's a project where someone else has done aone just for audio it. Video requires extra channels.https://hackaday.com/2015/11/02/escape-cable-hell-with-a-multi-io-audio-multiplexer/

author: IDEngineer
author_rank: Super Contributor
timestamp: January 26, 2023, 06:54:41 pm
content: Look up routing switchers, that's the system level solution. They come in audio, video, and both. Dig into how they handle things internally. I used to design those waaaay back in the 80's and at that time the signal path was done with discretes because there were no IC solutions with sufficient signal quality. Hard to believe that hasn't been addressed since. A bit of research should reveal something.

author: mkiijam
author_rank: Regular Contributor
timestamp: January 26, 2023, 10:51:13 pm
content: Quote from: IDEngineer on January 26, 2023, 06:54:41 pmSee my schematic back in the chat a ways. I beleive that's how it would be done the electro-mechanical way. The pure mechanical way is interlocking switches, but I hate those...

author: IDEngineer
author_rank: Super Contributor
timestamp: January 26, 2023, 10:55:59 pm
content: No, routing switches have an electronic signal path. They might have switches on the front panel to select the path, but the switching is done electronically. True even for the video versions, even back in the 80's. Nobody wants to use hard contacts for this stuff.

author: Benta
author_rank: Super Contributor
timestamp: January 26, 2023, 11:03:12 pm
content: I'm astounded that the knee-jerk reaction "throw an Arduino at it!" hasn't cropped up yet...

author: Ian.M
author_rank: Super Contributor
timestamp: January 26, 2023, 11:19:43 pm
content: Quote from: Benta on January 26, 2023, 11:03:12 pmNow you've done it!Using a cheap MCU to control analog switches (or similar) is entirely too obvious, and probably the best choice from a BOM cost perspective. If its for production, get them factory pre-programmed and drop-shipped to your PCB assembler.

author: themadhippy
author_rank: Super Contributor
timestamp: January 26, 2023, 11:29:12 pm
content: several methods are shown onhttps://sound-au.com/project163.htmQuoteT'is exactly what i done,and i try and avoid the buggers if at all possible,but after spending far to long in the rabbit hole i went for the easiest option, it also made controlling the relays for the switched attenuator much simpler.

author: paulca
author_rank: Super Contributor
timestamp: January 27, 2023, 09:36:52 am
content: Quote from: cantata.tech on January 26, 2023, 03:11:34 pmThis is a rather poorly implemented version of my current project. The difference is, all mine IO are digital and I don't want no stinking 1 to 1 routing nonsense. I want full many to many with mix and EQ.But overall it's the same goal. To not have to swap cables around to have multiple sources.

author: paulca
author_rank: Super Contributor
timestamp: January 27, 2023, 09:56:46 am
content: I have seen, what I consider, hacky techniques on my travels through audio forums. Mostly relating to digital streams, but the principle should still apply.Instead of switching the inputs per-sae, enabled/disable/mute inputs and wire them all together. So when you want to switch from one source to another, it just mutes one and unmutes another. Mutes or Enables. If you have 2 I2S devices, it will pull the enable pin high on one source and pull it low on the next. The sources carry on playing, it's just their outputs are disabled and only one at a time makes it to the next stage.In analogue audio terms a buffer opamp with gain of 0 or 1 for each input.For video, that might also work, depending on the video stream and the opamps.

author: mkiijam
author_rank: Regular Contributor
timestamp: January 28, 2023, 03:06:18 pm
content: Whether it is switching the MUTE or the INPUT or the OUTPUT or CREAM or SUGAR, the real issue for me is:Pressing one button "un" presses ALL others. It matters not what the buttons control. i.e. if they control mutes or source selects or when the cows come home.Just that there is an automatic deselect of everything else. THAT is the trick. Again, think of the mechanical interlock switch array or the schematic I drew.

author: David Hess
author_rank: Super Contributor
timestamp: January 28, 2023, 04:17:12 pm
content: Quote from: mkiijam on January 24, 2023, 05:57:19 amImplementations varied over time as technology changed.Modern implementations use CMOS switches and multiplexers. Before this, JFET integrated and discrete switches and multiplexers were used, and before this, "chopper" bipolar transistors were used.At higher frequencies there are bipolar transistor switches and multiplexers which work with currents instead of voltages and are often based on the Gilbert cell multiplier. One of the first, and longest lived, ICs Tektronix made for themselves was achannel switchfor operation up to 200 MHz.

author: Benta
author_rank: Super Contributor
timestamp: January 28, 2023, 08:15:22 pm
content: Quote from: mkiijam on January 28, 2023, 03:06:18 pmAlready posted in reply #6. It's impossible to select more than one input or output. Don't you read the answers?