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another CMOS logic switcher question
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celebutante



Joined: Jun 29, 2007
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PostPosted: Fri Jan 11, 2008 12:52 pm    Post subject: another CMOS logic switcher question Reply with quote  Mark this post and the followings unread

Some of you may remember a post I put up re building a voltage patching device for my modular using CMOS logic. Got kinda of sidetracked, so I'm fooling with it again. The idea has evolved into something like the old Sequential model 700 programmer, minus the digital memory (instead having just four presets selected with a switch).

Mainly it will use 4052 chips to switch between CV's preset with trimmer pots. But I want to use it do some audio routing as well (so I can switch the saw and sqr osc waves on/off).

Since I managed to blow up a 4052 yesterday trying to run audio through it (I guess they're strictly intended for DC voltages... cue laugh track from those more experienced than I), I'm pretty sure the correct way is to use a transistor, right? Or should I be using an op-amp? How might I implement that?

thanks....

mitchell
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celebutante



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PostPosted: Fri Jan 11, 2008 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just found this:

http://www.uni-bonn.de/~uzs159/

then go to "misc/signal switch"

But it's a bit confusing, because it appears that there's a a resistor/transistor combo hooked to the 4053's address lines; can't see why you'd do that. I guess the A, B, C of the 4053 isn't meant to represent the address lines, but instead the signal outputs from the the three lines above (and the switch shown in the three identical diagrams is just a manual two pos input selector switch?)... anyone?

mitchell
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blue hell
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PostPosted: Fri Jan 11, 2008 7:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

The transistors are just inverters on the address lines, probably for matching it to an active low control circuit ... but the switches above just represent the the ones in the IC, not manual ones anyway. No need to get confused Very Happy
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also .. could someone please turn down the thermostat a bit.
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PostPosted: Fri Jan 11, 2008 7:21 pm    Post subject: Re: another CMOS logic switcher question Reply with quote  Mark this post and the followings unread

celebutante wrote:

Since I managed to blow up a 4052 yesterday trying to run audio through it (I guess they're strictly intended for DC voltages... cue laugh track from those more experienced than I), I'm pretty sure the correct way is to use a transistor, right? Or should I be using an op-amp? How might I implement that?

thanks....


Without a circuit it's a bit hard to answer ... the CMOS switches can handle AC alright, but but they can't handle signals below ground or above Vcc at all, and they might be killed if you try.

Do you have a circuit diagram somewhere?

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also .. could someone please turn down the thermostat a bit.
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celebutante



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PostPosted: Sat Jan 12, 2008 1:13 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm basically using the Digisound 80 switcher circuit, except that I'm using a 4052 instead of a 4051 (4051 is a 1>8 mux, 4052 is a dual 1>4 mux). But my voltages are all the same as this.

I attempted to route a triangle wave from one my .com oscillators, which output 10v peak to peak, but I ran it through a passive attenuator. It sounded really weird and distorted, then when I played with the level on the attentuator, it just died.

Vcc is +15v, so I don't think that's a problem. But wouldn't an oscillator wave be an AC signal fluctuating between +5v and -5v (unattenuated)? i.e. below ground causing CMOS to fry? This my theory... if it's correct, how do I can a route a bipolar waveform through? (I think I'm missing something!)

mitchell


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bugbrand



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PostPosted: Sat Jan 12, 2008 2:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Heya,

You can run 4000 series chips off +/- 7.5v safely - you'll see this in some Buchla designs (eg. LoPassGate, I think -- yup, check Mark Verbos' site: http://www.simple-answer.com/DIY.html)

Also, may be worth checking a CGS design, the Sequential Switch - I ain't totally figured it, but he's usually got some great ideas:::
http://cgs.synth.net/modules/cgs28_seq_switch.html

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fonik



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PostPosted: Sun Jan 13, 2008 9:30 am    Post subject: Reply with quote  Mark this post and the followings unread

or even from +8V to -8V, that's what doepfer does on his switch.
according datasheet it is rated for operation from 0.5V-18V...

here is a link to my redrawn schematic:
http://modular.fonik.de/pdf/seq_switch.pdf

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richardc64



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PostPosted: Sun Jan 13, 2008 10:11 am    Post subject: Reply with quote  Mark this post and the followings unread

celebutante wrote:
...it appears that there's a a resistor/transistor combo hooked to the 4053's address lines; can't see why you'd do that. I guess the A, B, C of the 4053 isn't meant to represent the address lines, but instead the signal outputs from the the three lines above (and the switch shown in the three identical diagrams is just a manual two pos input selector switch?)... anyone?

mitchell


No no no. The switches shown in the 3 identical diagrams represent the 3 analog spst switches within the 4053. They are controlled by the three transistors, which are there to protect 4053 control inputs from voltages greater than the 4053 positive supply.

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celebutante



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PostPosted: Sun Jan 13, 2008 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks again all... I'm sure I can it going with all this info! I'll keep ya posted... right now I'm building A couple of Rene Schmitz 555-based envelopes which will be part of it (since I can't voltage control my .com envelopes, I realized I should just incorporate them, like the Sequential 700 programmer).

Mitchell
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françois



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PostPosted: Mon Jan 14, 2008 4:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello,

Just a few remarks. If you read carefully the datasheet for the 4051/4052/4053 switches, you'll notice that they have three supply voltages : VDD, VSS and VEE.

VDD and VEE are the analog signal rails, and VDD-VEE can be as high as 20V (but 15V or maybe 18V is safer).

VDD and VSS are the logic control rails and can also be as high as VDD-VSS=20V. This allows switching analog signals such as ±5V pk-pk under control of 0/+5V logic. Or ±5V logic as I like it (using a LFO as a clock for example).

These switches will happily accept AC inputs, within a limited bandwidth of course (they are CMOS, not known for its very high speed). At audio rates this is not a problem. But never ever have the analog or logic signal exceed the rail supply voltages ! Unless you mean to build an electronic fireworks...

-- françois
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richardc64



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PostPosted: Mon Jan 14, 2008 5:55 am    Post subject: Reply with quote  Mark this post and the followings unread

me wrote:
[The switches shown in the 3 identical diagrams represent the 3 analog spst switches within the 4053.


Ooops. That should be "3 analog spDt switches..."

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