Digital volume control w/rotory encoder (no MC)

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Many of the DIYs are lucky to have less limitations on knowledge, availability, affordability etc,etc......and many are not (I belong here).

Considering all this, I need help in designing a Digital Volume Control with a rotory encoder.

The digital will be totally hardware based, minimum components, less prone to obsolescence and maximum flexibility for present and future use.

Presently I am like...
Rotory encoder---up/down counter(LSI)---D/A converter---VCA
How bad am I?

I am not sure, which VCA ic for high end audio.

Kindly help with your ideas refering to IC numbers

Thanks all in advance

Gajanan Phadte
 
up/down counting from rotory encoder

The rorory encoder can be connected (with pull ups)directly to the two inputs i.e. count and up/down of ICM7217 and we have half the circuit.
For startup volume, 2 thumbwheel switches with a little circuitry will work fine
All we need is a roll-over circuit for the counter (counts upto 9999).
After all we don't need a 10000 step attenuator.
Now we need an 8 bit D/A for 256 step attenuator.

Which cheap 8 bit D/A?...
any ideas...

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Gajanan Phadte
 
Errata

Thanks till.
I would love to do it but I am more confident without the MC.
India is a large country and buying over the counter is only the option at Goa and many places. Moreover no possibility of postal purchase or import, due to high duties.

Now the errata...
May be the fellow DIYs have not analyzed the possibility.

For those who are quick to construct, I should mention...
The rotory encoder connected to the ICM7217 will work fine, and digit display of whatever type needed can be connected, using appropriate driver if LEDs are not the choice.

1)Having a 4 digit counter, we will not get 256 steps, but will get 10, 100, 1000 or 10000steps.
2)The output of the counter will be multiplexed BCD and not binary. So a demux and BCD to binary converter will be needed.
3)Simple additional circuitry will be needed to stop change of output from 00 to 99 and 99 to 00. The counter has outputs 'equal and zero' and are useful for this purpose.

For those of you who want to make a step attenuator, connect the relays and resistors as in Jill's site and you are ready to go.

Use a motor to rotate the encoder and go remote.

Gajanan Phadte
 
ICM7217

The datashheet is here
pdfserv.maxim-ic.com/en/ds/ICM7217.pdf

The register has to be loaded on power on with the step numbers -1 required.
The zero output has to be ORed with the UP/Down and the EQUAL output also has to be ORed with the invert of UP/DOWN

The two outputs of ORs will be connected to the control pin of switch 4066, that are connected in series. The count will be routed thrugh these two switches, and the UP/DOWN will be connected directly to ICM7217 Up/Dn input.

Can anybody draw the schematic and put it on.

Will come later...

Gajanan Phadte
 
I forgot to mention, my last post is my way of tackling ...

3)Simple additional circuitry will be needed to stop change of output from 00 to 99 and 99 to 00. The counter has outputs 'equal and zero' and are useful for this purpose.

We will still need to design for max count which is loaded into the register at power on.

Gajanan Phadte
 
Why use a bcd counter and then convert to 8-bit? Wouldn’t it be easier to use a 8-bit counter in the first place? Btw, if you found a way to do bcd ->8 bit without resorting to mc please let me know. I’ve search a lot for this and haven’t yet found a solution.
Check out my posts in this thread, there’s a schematic there for a simple bcd or 8-bit counter. It can be controlled with a rotary switch instead of a rotary encoder.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=1404&perpage=10&pagenumber=2

Cheers
 
Other counters

The rotary encoder cannot be connected directly to the other counters.
Interfacing the encoder to these counters will need a much larger logic between the two. Whereas the solution of demux and BCD to binary converter is straightforward and very simple to design.

I will give quick top of the head answer...
1)Burn a eprom with the lookup required
2)Decode the BCD and than encode to binary

With the above two methods, you can probably change the BCD to anything you want. However there are BCD to binary encoder in TTL and most of them are now 40HC....

Will come later after search.

Gajanan Phadte
 
less prone to obsolescence and maximum flexibility for present and future use.

These are first priorities.

It's a good IC but...
DS 1666 is not available in the local market

How flexible is it...

*The counter has a register which can be loaded with any value from 1 to 9999, so u can get 2 to 10000 step control without any additional hardware, just by setting the thumbwheels, at least upto what is suggested. Higher value preferred for high Wattage amps. If this feature is not needed, just hardwire the needed value.
*You can load the poweron volume level
*Has a display of your choice
*It has a modern human interface, the rotary encoder.
*Easy to turn into remote and will give the good old feature of a rotatng motorised pot.
*The control from a micro can be realised using micro-compatible counter ICM7227, if someone desires

Cheap control of volume can be realised with a FET around an audio quality op amp and use opamp that suits your budget.

Learning advantage is an additional benefit

Regards,

Gajanan Phadte
 
gmphadte, thanks for finding that ic, to bad its obsolete.. Looks like it would be perfect for my next project.
The controller I’m doing for my next amp is a 6-bit relay volume controller with 7 segment display for visual level indication.. So far the design consists of 6 ic’s. I already have most of the ic’s, so its not a matter of cost (there all cheap anyway) but it consumes a lot of board space.
I don’t have a pic programmer, and I know absolutely nothing about programming, burning EPROM etc. so I try to get by using only “off the shelf parts”. Your ideas seem very interesting but I fear some sort of programming would bee required?
 
programing the EPROM...

The programming of an EPROM can be done on a breadboard. However you will have to generate the required states using swithes and will have to feed programming supply apart from logic supply. Advantage is that you need only one EPROM.

The other solution-- decoding and encoding is easy.
You will have to use CD4514 for decoding and MC14532(8 bit priority encoder) for encoding to binary. However you will have to cascade the 4532s. It's given in the datasheet.
http://convergence.chez.tiscali.fr/info/td3/mc14532.pdf

Now you will have...

BCD---CD 4514---decoded decimals---MC14532---binary

Gajanan Phadte
 
Thanks for the suggestions.
Till has almost convinced me to learn pic programming, so maybe I will try that. Otherwise I think I'll just parallel the count up/down terminals of two bcd and binary counters. I think that will be just as easy as doing bcd to binary conversion.
 
learning PIC programming...

Till has almost convinced me to learn pic programming,

That's a good thing and with the present trend, everybody who has access to the tools and who can, should do it.

I just showed u a solution, which u thought could be done with MCU

I am sure many 5% THD+N (low enders and beginners) learned an idea.

Gajanan Phadte
 
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