Digital volume control w/rotory encoder (no MC) - diyAudio
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Old 26th September 2004, 08:00 AM   #1
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Default Digital volume control w/rotory encoder (no MC)

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
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Old 26th September 2004, 11:03 AM   #2
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Default 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...

-------------_________---------__--_-_--_-_-
Gajanan Phadte
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Old 26th September 2004, 11:22 AM   #3
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DAC0808 would be a cheap one. But i really suggest PGA2310 or 2311 controlled with a small MC: http://home.tu-clausthal.de/~tpa/PGA/index.html
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Old 27th September 2004, 06:13 AM   #4
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Default 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
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Old 27th September 2004, 01:06 PM   #5
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Default 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
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Old 28th September 2004, 05:46 AM   #6
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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
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Old 28th September 2004, 05:41 PM   #7
Kermit is offline Kermit  Norway
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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.
Idea for a better volume control...

Cheers
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Old 29th September 2004, 06:04 AM   #8
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Default 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
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Old 29th September 2004, 06:18 AM   #9
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Default decoder

If you are into 10 step control, just drive the relays(one at a time) using some ULN series driver ICs/transistors after the decoder.

In this case you will have...

Rotary encoder---ICM7217---Demux---Decoder---Drivers---Relays

Gajanan Phadte
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Old 29th September 2004, 06:28 AM   #10
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Default Digital with pot

Use a pot to feed an LM3914/5 in dot mode and drive relays
Now you have a cheap step attenuator with ordinary potentiometer and with LED position indicator

Good idea for multichannel control also

Which VCA?...

Gajanan Phadte
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