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'[OT] Analog rotary switch using a chip!'
2014\05\21@210211 by Richard R. Pope

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Hello all,
    I don't know how to word this question. I would like to use some type of analog multiplexing chip in place of a multi-position, mutli-deck mechanical rotary switch. Let's say that I want to have several different inputs that are to be routed to several different circuits and after processing they are then sent to some type of instrument. I can do this with a mutli-position, mutli-deck mechanical rotary switch. Is there some type of analog switch that I can use in place of this so that I can use a mutli-position single deck switch? I know what I want to do but I don't know how to explain it. Any thoughts anyone??
Thanks,
rich!
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2014\05\21@211307 by John Gardner

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....I know what I want to do but I don't know how to explain it.

I've made that mistake too...  :)

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Eppur, si muove...
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2014\05\21@212222 by Steve Smith

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face
Lets start with a specification that is a little narrower.... look at the
cmos 4051,2,3. These all fit your requirement but differently
Steve

{Original Message removed}

2014\05\21@212722 by IVP

face picon face
> Any thoughts anyone??

4051 springs to mind

http://www.nxp.com/documents/data_sheet/74HC_HCT4051.pdf

There are many variants

Joe
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2014\05\21@214529 by IVP

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PS,

to use a 4051-type IC with a rotary switch I'd look at using the
ADC of a micro to control S0, S1, S2 and chip enable(s)

I've not done this with a switch but have with a detented pot

So for, eg, a 12-way 1-pole rotary, the 10 innermost terminals
have a resistor such that its selection forms part of a divider to
give a distinct and discrete voltage for the ADC. Positions 1 and
12 can be Vss and Vcc respectively

As each IC is only a 1-of-8, use the micro to select any of a
group of ICs for as big a bank of switches as you need

Some old projects of mine (pre-ADC PICs)

http://home.clear.net.nz/pages/joecolquitt/0pots.html

http://home.clear.net.nz/pages/joecolquitt/mixer.html

Joe

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2014\05\22@215543 by Richard R. Pope

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Joe, Steve,
    Thank-you for the suggestions. This is what I am looking for. Right now I am experimenting with a CD4066. I don't have any 4051s right now but the 4066s are helping me to design a control system.
rich!

On 5/21/2014 8:45 PM, IVP wrote:
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2014\05\22@220656 by IVP

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> I don't have any 4051s right now

As I mentioned, there are quite a few analogue switch ICs

Google 1-of-8 analog before you buy. I suspect 4051 will be
cheapest and perfectly OK for most analogue applications but
another may suit you better

Joe
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2014\05\23@042556 by alan.b.pearce

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> Joe, Steve,
>      Thank-you for the suggestions. This is what I am looking for. Right
> now I am experimenting with a CD4066. I don't have any 4051s right now
> but the 4066s are helping me to design a control system.
> rich!

Another one to look at is the venerable DG403 series of chips. Has logic level control, but the switch can deal with +/-12V (when using appropriate supply rails). Main disadvantage is it is a 3 rail supply (5V logic and +/-12V analogue). IIRC the DG403 has 2 switches in a package, I don't know for sure if there are others in the family have more, but I have a feeling there is a quad version.
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2014\05\24@213842 by Richard R. Pope

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Alan,
    Thank-you for the information.
rich!

On 5/23/2014 3:23 AM, spam_OUTalan.b.pearceTakeThisOuTspamstfc.ac.uk wrote:
>> Joe, Steve,
>>       Thank-you for the suggestions. This is what I am looking for. Right
>> now I am experimenting with a CD4066. I don't have any 4051s right now
>> but the 4066s are helping me to design a control system.
>> rich!
> Another one to look at is the venerable DG403 series of chips. Has logic level control, but the switch can deal with +/-12V (when using appropriate supply rails). Main disadvantage is it is a 3 rail supply (5V logic and +/-12V analogue). IIRC the DG403 has 2 switches in a package, I don't know for sure if there are others in the family have more, but I have a feeling there is a quad version.

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2014\05\26@224958 by Richard R. Pope

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Hello all,
    I found a circuit that uses the CD4066 quad analog switch that works well. The on resistance at 12 volts is about 32 ohms. The off resistance is more than 10 megaohms. I see two draw backs with this circuit. The first is the 32 ohm on resistance. This means that the input resistance to the down stream circuit must be pretty high. Probably over 10K would be best. The other is that it requires 8 switches, 2 chips to switch two circuits. Each additional circuit requires an additional 4 switches or one chip.
    Two switches are connected in series. One switch is used to ground the output of the first switch when the circuit is in the off state. The fourth switch is used to control the gating of the first two switches. I could add another switch in parallel with the output switch this will drop the output resistance to under 16 ohms. In fact if I were to put two switches in parallel the output resistance would drop to under 8 ohms. This would mean that it would take three chips for every two poles.
    The on resistance of one switch at 12 volts is around 16 ohms and the off resistance is about 30K ohms. So this design increases the the off resistance by a factor of over 350 times. It only doubles the on resistance. So this is a good circuit. The complication is not a big deal as these chips are only about 50 cents each. So even after adding a socket , the three pullup resistors, and a decoupling capacitor for each chip the cost is still only about $1 per pole. With three switches in parallel the cost would be about $1.50 per pole. This a lot cheaper than rotary switches that can perform the function. This is also a lot more reliable since the only current flowing through the rotary switch contacts will be only a few milliamps at 12 volts.
    Thanks everybody for all of your help. If anyone has any other suggests please feel free to weigh in.
Thanks,
rich!

On 5/23/2014 3:23 AM, .....alan.b.pearceKILLspamspam@spam@stfc.ac.uk wrote:
>> Joe, Steve,
>>       Thank-you for the suggestions. This is what I am looking for. Right
>> now I am experimenting with a CD4066. I don't have any 4051s right now
>> but the 4066s are helping me to design a control system.
>> rich!
> Another one to look at is the venerable DG403 series of chips. Has logic level control, but the switch can deal with +/-12V (when using appropriate supply rails). Main disadvantage is it is a 3 rail supply (5V logic and +/-12V analogue). IIRC the DG403 has 2 switches in a package, I don't know for sure if there are others in the family have more, but I have a feeling there is a quad version.

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2014\05\27@001308 by IVP

face picon face
> If anyone has any other suggests please feel free to weigh in

The 4066 element can be used as a digitally-controlled variable
resistor, or used to switch another resistor, if you feel the need
for volume control such as balancing

Drive the Control pin with PWM that has a variable duty cycle,
and the resulting effective resistance is proportional to that

R x (On time / Off time)

A not-unknown technique in semi-digital applications, such as
early synthesisers, to vary multi-pole filters etc with a single
control voltage that alters a common PWM driver section

PWM frequency an be several hundred kHz to avoid aliasing
with the audio signals

Joe
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2014\05\27@002241 by Richard R. Pope

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Joe,
    Thank-you, I'll keep that I mind. Right now I'm just interested in the switching capabilities. I'm using it in place of a multipole rotary switch. Multiple inputs are sent to multiple processing stages and then sent to the appropriate output.
rich!

On 5/26/2014 11:13 PM, IVP wrote:
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