Replacing pot with digital volume control

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puterfixer

puterfixer

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Joined 2001
blog.websurf.ro/
#1
Hi everyone,

I have a set of satellite speakers and subwoofer made by Cambridge SoundWorks. The subwoofer has an amplifier built-in, and connects with a cable to any stereo headphone jack or RCA line out jacks (through an adapter). The cable has a simple inline potentiometer to adjust volume, like an attenuator.

I would like to replace that potentiometer with an unit with digital control of the volume, Mute and Power on/off setting, which should be operated via an infrared remote control. The idea is to connect the speaker set through this unit to any audio source (like VCR, or satellite receiver, which don't have built-in volume control) and be able to adjust the volume from anywhere in the room. If possible, it would be great for the unit to retain volume level while powered off.

If anyone could help me build such an equipment, I'd really appreciate it. I'm not an electronic graduate, so take it easy with me... any information will help: web pages, schematics, suggestions for circuits, anything. I live in Eastern Europe, can mail order most circuits and equivalents from a nearby components distributor. Thank you kindly for your time,

Best regards,
Mr. Titel
 
#2
Hello,

I am sorry but I don't know any kit who peform your task, but one thing: if you install digital component in your amplifier (like digital potentiometer), you need a separate power supplie to be sure that you don't introduce noise in your signal path and amplifier power supplie.
 
#4
I'm using the Dallas Semiconductors DS1802 in my preamp
(see http://www.soton.ac.uk/~apm3/diyaudio/Preamp.html),
though I'm afraid I can't comment on its sound as I'm
still working on the control circuitry and haven't
connected the preamp to my system yet.

Dallas have a datasheet for DS1802 at
http://www.dalsemi.com/datasheets/pdfs/1802.pdf .

By the way, you don't need a separate power supply for this
chip, since it doesn't have a high frequency clock. I used
a low-power LM317 regulator to get a +5V line for the
DS1802 from the +15V preamp supply. What I did do, though,
was to use optoisolators to separate the ground lines of
the audio circuits from the digital circuits.

Alex
 
#5
This guy used to sell a neat kit that would decode the IR burst from any remote control, then gives you seven output pins for controlling a device. You could easily use his circuit to operate a motor driven potentiometer. I have.
I think he now just sells the PIC controller with instructions for the rest of the circuit. Go to weedtech.com and look for the "infrared receiver kit" under the "hobbyist " section

http://www.weedtech.com/index1.html[/url]
 
#6
Great ideas, everyone, thanks for your replies!

I was using the wrong keywords in web search engines, so as soon as I entered <b>+digital +potentiometer +volume +control</b> in <a href="http://www.google.com" target="_blank">Google.com</a> the useful links started to pop on screen. There were a number of IC manufacturers with good chips for digital volume control, some with up/down buttons and others with 3-line serial input which is great for interfacing with an infrared receiver and decoder.

For those interested in similar applications, check out these manufacturers' web sites:<ul>
<li><a href="http://www.dalsemi.com" target="_blank">Dallas Semiconductors</a> - check series <b>DS18xx</b> and <b>DS16xx</b>
<li><a href="http://www.analog.com" target="_blank">Analog Devices</a> - check series <b>AD52xx</b> and <b>AD84xx</b>
<li><a href="http://www.crystal.com" target="_blank">Crystal<a> - <b>CS3310</b> appears in a number of articles online.
</ul>

Now, all I got to do is see if my local components distributor carries these chips or compatibles, and see where to go from there. I still need to find an IR decoder chip, one of the pages posted above has a kit with an IR decoder with learn function, which is pretty cool - if I could find out what that IC is. Again, thanks everyone for your time, much appreciated!

[Edited by puterfixer on 04-24-2001 at 12:09 PM]
 
#7
There is also the Analog Devices AD7110, AD7111, AD7112, AD7112A, AD7115 and AD7118. These were made for audio use, although I'm not sure which of these are still in production.

There was a slick idea in one of the Analog Devices Application guides for a precision attenuator (0 to 80 dB range) with 0.1dB steps. Make a great volume control....

Michael
 
#8
" I still need to find an IR decoder chip, one of the pages posted above has a kit with an IR decoder with learn function, which is pretty cool - if I could find out what that IC is."

jbateman replies...
The part that weedtech still sells is actually a PIC microcontroller, with his own code burned in it. Poke around his site and you can find part number PIC-RCR, microcontroller w/ documentation...$16. Unless you're really talented I don't think you can do this part yourself.

Good luck!
 
#9
Hi,

Conrad sells ab pcb with the circuit you need. It comes with all the parts you need except for the resistor chip, but they also sell it separately, so you can order the entire thing from them. It is a mono kit so you have to order two for stereo use. It uses two buttens for up/down but it says in the catalog that you can use Ir as well.

You can find there site at http://www.conrad.com

Roel
 
#10
IR

If you want a simple IR receiver use an IR reciver with built in decoder (demodulator) you can then use any type of PIC or similar and a remote control you presently own to control the digi-pot.
I've already used one so let me know if you need a few pointers. In many ways its better than just buying an IR module because you can configure the amount of buttons you need.
Hope this helps.
Knuckles
 
#11
knuckles_mctug Thanks, I already have a PIC schematic for an IR receiver for the computer serial port, will fiddle with it sometime in the future. My difficulty was to find a good chip to vary the volume on both channels (not necessarily with balance function, or mute etc); most of the schematics and diy projects I've seen were using a 16-stage counter with resistors in between, but those don't make a smooth volume variation, and also produce audible "clicks". As of now, I'm still looking around for a good schematic; perhaps after I build a PIC programmer and get to learn how to do that myself, I'll do the digital volume control as well. Thanks for the suggestion tho!
 
#12
The DS1802 is easy to use and can be used as a standalone Electronic Dual 50K Pots that can be programed in alot of ways, Without requireing a digital interface like the CS8010? Chip. But otherwise if the input signal voltage is less than 2.5 volts RMS it will work Fine. If overloaded it Misbehaves badly.
 
#13
The Audio Evaluation Report for the DS1802 (posted on
Dallas' own site) is interesting and useful, but it leaves
out one crucial piece of information. The tests are
reportedly carried out out with a "1VRMS" input signal, but
it isn't specified whether this is centred about 0V
(analogue ground) or floated between ground and +5V. The
data sheet insists that voltage at any point should be
between -0.7V to +7.0V, which precludes negative signal
excursions, and suggests that keeping signal levels below
2.5VRMS, as ppl suggests. I floated the ground on mine
by attaching the AGND pin to -2.5V and the VCC pin to +2.5V
(unfortunately disabling the zero-crossing function in the
process).

The apparently rising IMD level with decreasing signal
amplitude had me puzzled - this is normally a sign of
crossover distortion (as devices switch off at zero
crossing), but if the measurements are made with a signal
which is always positive relative to ground this must be
noise, rather than distortion (I assume).

In my preamp I follow the DS1802 with an output stage with a
gain of 10dB, so that 3.5VRMS will clip the latter anyway. I
also put 10dB of attenuation on the CD input to ensure that
2VRMS full level doesn't doesn't stretch the volume control
too far.

Don't ask how the preamp sounds, as I'm still struggling
with the control connections fro the volume control...

Alex
 
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