Author Topic: digitally controlled stepped attenuators..??  (Read 34584 times)

kruz

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digitally controlled stepped attenuators..??
« on: June 22, 2004, 07:28:15 PM »
following some ideas i had some time ago, and remembering the great Mikkel (mcs) relay switching board, i tought that maybe for my upcoming api clone i could use a digital stepped attenuator system..
let me explain:
a simple rotary encoder, a 2 or 3 digit 7 segment led display (to show the db value) and mcs's relay switching board..
how to connect all this?
well.. i don't know :green:
DaArry told me something like: "maybe we could use the mios here"..
see the mios system here: http://www.ucapps.de
found also some more documents about this:
http://www.ucapps.de/midio128.html
http://www.ucapps.de/midio128/relay_example.pdf
why all this?
well..  recallable settings (even via midi), no need to source hard to find rev log pots, probably cheaper then the pots if you do some mic pre channels in one box, no audio loss cause good relays and 1% metal resistors are better then most of the pots.. also..this "interface" could be used in any other mic pre... the only thing to change will be the resistors value, to match the mic pre original attenuator design.
So, what do you think?
who could help me here to design and troubleshoot this project?
this could be an interesting "new era" add on to any project and surely a future GroupDIY project age somehwere :wink:
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mcs

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digitally controlled stepped attenuators..??
« Reply #1 on: June 23, 2004, 06:50:17 AM »
If you want something simple, you could use a small board like the one I made for Fabio Bauman (Mr. Bauman - please post a photo :wink:).

You can see a drawing here:


The actual size is about 5*5cm. You could just replace the two pushbuttons with a rotary encoder. The board countains two LED displays. It cannot be controlled using MIDI, but RS-232 or IR is no problem. Perhaps MIOS also supports RS-232?

Best regards,

Mikkel C. Simonsen

kruz

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digitally controlled stepped attenuators..??
« Reply #2 on: June 23, 2004, 07:04:38 AM »
this one looks extremely cool..
i want to go the simple way.. don't really need midi recalling..
am i correct if i say that this pcb you shower here is just for the encoder and its display?
i can't see the relays and teh resistors..
could you please post some schems?
this one seems the way to go..
thank you very much Mikkel..  :thumb:
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mcs

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digitally controlled stepped attenuators..??
« Reply #3 on: June 23, 2004, 07:21:58 AM »
I have already posted the schematics, so I guess Littlebush has the copyright now :wink:

Here is the schematic: http://stiftsbogtrykkeriet.dk/~mcs/RelPot_sch.gif

The schematic covers both the control board and the relay board.

The board with the relays can be seen here:


The relays are standard DIL relays.

Best regards,

Mikkel C. Simonsen

kruz

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digitally controlled stepped attenuators..??
« Reply #4 on: June 23, 2004, 07:29:10 AM »
Great!!!
thank you very much again Mikkel...
i'll try to figure out all the rest by myself, but i'm not sure that i can do this :green:
anyway.. i'll post here my questions..
it seems that the realy board have 16 steps.. am i right?
i was thinking that it would be better to have more steps for my attenuator.. but maybe 16 are enough.
thank you thank you :grin:
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mcs

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digitally controlled stepped attenuators..??
« Reply #5 on: June 23, 2004, 07:32:18 AM »
No, it has 256 steps from 0R to the max. value you decide. I think Bauman is trying to make a rev. log pot also.

Best regards,

Mikkel C. Simonsen

daArry

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digitally controlled stepped attenuators..??
« Reply #6 on: June 23, 2004, 09:11:40 AM »
Hey fellaz...

I'll def be gettin jiggy on a MIOS adaption based on mcs' methods - but not for a while as I really gotta finish some other bits on the bench beforehand...have found some cheap relays I'm looking to get now tho :)

any brd layouts/howto's etc will of course be posted here so all should be good...:)

Peesh

SmashTV

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digitally controlled stepped attenuators..??
« Reply #7 on: July 02, 2004, 01:00:10 PM »
Hello!

First off thanks to Kruz for the invite to the new home!
Its great to see this community re-establish itself in such a strong way!
I was only a lurker at the old place, with all the open projects I have I thought it best not to start something new.  : )

Anyway, I'm having troubles understanding the relay board schematic.
I'm assuming that R1 and R16 have an inverse relationship to each other, with R1 at the lowest chosen resistance level and R16 as the highest out of the 8 values used.

So assuming R1 is 20R and R16 is 2.56K, according to the schem with the relay @ rest you would get 20 ohms between pins 1+2 (of the pot connector), but in the same state R16 would be bypassed by the relay, not giving the 2.56K ohms between pins 2+3 that is expected.

Should the second set of throws/contacts of the relay swap for proper operation?

My sincere apologies if I have missed the obvious and assumed wrong here!   :grin:

Best Regards!

SmashTV

mcs

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digitally controlled stepped attenuators..??
« Reply #8 on: July 02, 2004, 01:19:27 PM »
Quote from: "SmashTV"
Anyway, I'm having troubles understanding the relay board schematic.
I'm assuming that R1 and R16 have an inverse relationship to each other, with R1 at the lowest chosen resistance level and R16 as the highest out of the 8 values used.

R1 and R16 should be the same value. R2 = R15, R3 = R14 etc. R1 is the smallest value and R8 the largest.

That way the resistance between 1 and 3 will be constant and the resistances between 1 and 2 and 2 and 3 will change.

Quote
Should the second set of throws/contacts of the relay swap for proper operation?

No, just swap the resistors to the correct positions :grin:

Best regards,

Mikkel C. Simonsen

SmashTV

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digitally controlled stepped attenuators..??
« Reply #9 on: July 02, 2004, 01:52:12 PM »
Thanks Mikkel!

Time for some tinkering....
 :grin:

SmashTV


rafafredd

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digitally controlled stepped attenuators..??
« Reply #10 on: July 02, 2004, 03:30:05 PM »
Mikkel, can you post the ready to transfer PCB Layout and/or Gerber files?

mcs

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digitally controlled stepped attenuators..??
« Reply #11 on: July 02, 2004, 03:56:22 PM »
Quote from: "rafafredd"
Mikkel, can you post the ready to transfer PCB Layout and/or Gerber files?

Yes, I'll have a look at it later today.

Best regards,

Mikkel C. Simonsen

mcs

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digitally controlled stepped attenuators..??
« Reply #12 on: July 02, 2004, 06:58:25 PM »
The PCB files and a short description is on my website now.

[edit]I have a spare PCB if anyone needs it BTW[/edit]

Best regards,

Mikkel C. Simonsen

Kev

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digitally controlled stepped attenuators..??
« Reply #13 on: July 02, 2004, 07:10:51 PM »
Does anyone here genuinely have some MIDI construction knowledge as I have two projects I'd love to get off the ground.  These could be combined into one.

I just don't have all the skills required to make this one fly.
Kev
DIY Factory

rafafredd

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digitally controlled stepped attenuators..??
« Reply #14 on: July 02, 2004, 07:26:10 PM »
Great.

I downloaded it already.

I had a look at your site and you have nice stuff there.

Do you sell PCB´s for your projects? I would rather buy the PCB´s from you instead of doing my own, so that I can help support the great stuff yu bring to us.

If you don´t sell PCBs, let us see the files for the control PCB also, so that we can etch our own PCBs for this great project.

It makes DIY enter in another level, I think!!!

Imagine those API clones with digitally controlled gain... For the hell with those rev log pots!!!   :twisted:

daArry

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digitally controlled stepped attenuators..??
« Reply #15 on: July 02, 2004, 07:36:34 PM »
Quote
Does anyone here genuinely have some MIDI construction knowledge as I have two projects I'd love to get off the ground. These could be combined into one.


I've made a few midiboxes built around the stuff at ucapps. Chek the forum: http://forum.midibox.org/ and post ur requirements there to see what the dilly is...

mcs

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digitally controlled stepped attenuators..??
« Reply #16 on: July 02, 2004, 07:45:28 PM »
Quote from: "rafafredd"
I had a look at your site and you have nice stuff there.

Thanks!

Quote
Do you sell PCB´s for your projects? I would rather buy the PCB´s from you instead of doing my own, so that I can help support the great stuff yu bring to us.

Yes I do sell PCBs. I order PCBs for hobby stuff when I have leftover "holes" in the panels I order. That's also why I have a relay board now...

Quote
let us see the files for the control PCB also

I made that small control board as a test, and I think Fabio Bauman is testing it currently (Fabio? Are you there?). I will probably replace the pushbuttons with a rotary encoder, and make the pot taper programmable. But what features do you need on the control board? Buttons, controls, displays etc.

Best regards,

Mikkel C. Simonsen

Rochey

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possible alternatives.
« Reply #17 on: July 02, 2004, 08:50:33 PM »
Heya guys... I'm new to the board (been lurking for about a week and a bit... but getting increasingly tempted to post).

It's seems bizarre to me why you'd use such a system of relays etc. Have you considered using something like the TI PGA2311/0 digitally controlled volume controls?

Let me get this out the way as well (just in case i'm recognised from other online music groups I contribute to) -- I work for TI. Having said that, I have a strong interest in DIY Audio, and will happily look at competitors parts if they suit the application better. (in other words, I do my best to be unbiased). :oops:

Back to my point, the PGA2311/0 come in Thru hole packaging, so there isn't much need to go surface mount if you don't like the idea of doing that. You can also easily control it from a micro or your pc. It's a very simple serial port that is programmed with only a few control pins.

For the processor, you may not even need to use a a micro with an operating system (such as MIOS). If all you want to do is take control signals from a rotary encoder, then why not use something like an MSP430 (get cheap kits from TI or Olimex), and have a very simple program that polls (checks) the input pins from the encoder every 1mS, then sends a serial code to the volume control, based on the change in setting.

Very very very very simple stuff (i'm in sales & apps, and even I can do it!). If your interested, please feel free to drop me an email - Rochey69 at the warm mail. com :D --  or even better start a new thread where we can discuss it more!

Cheers guys.

R :thumb:
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mcs

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Re: possible alternatives.
« Reply #18 on: July 02, 2004, 09:01:35 PM »
Quote from: "Rochey"
It's seems bizarre to me why you'd use such a system of relays etc. Have you considered using something like the TI PGA2311/0 digitally controlled volume controls?

Most of the people here are not trying to make volume controls - they need pots with strange tapers. You could use digipots, but they are not that great (most of them anyway). They have a small number of steps and a very limited voltage range. They also add distortion that the relays don't...

Quote
For the processor, you may not even need to use a a micro with an operating system (such as MIOS). If all you want to do is take control signals from a rotary encoder, then why not use something like an MSP430 (get cheap kits from TI or Olimex), and have a very simple program that polls (checks) the input pins from the encoder every 1mS, then sends a serial code to the volume control, based on the change in setting.

That's what I am doing (I'm not the one with crazy ideas :wink:), except I use 8051 type controllers. My control board discussed in this thread uses a AT89C2051 for controlling the relays, driving the displays and reading buttons/encoders - can't get much simpler than that... But I won't mind using a TI chip if you make anything with a '51 core :grin:

Best regards,

Mikkel C. Simonsen

SmashTV

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digitally controlled stepped attenuators..??
« Reply #19 on: July 02, 2004, 09:03:40 PM »
Quote from: "Kev"
Does anyone here genuinely have some MIDI construction knowledge as I have two projects I'd love to get off the ground.  These could be combined into one.

I just don't have all the skills required to make this one fly.


Heya Kev!

What are you needing to do with MIDI?  I am currently tinkering with MIDI I/O using smaller AVR MCU's.  I'm also very heavy into the MIDIbox projects http://www.midibox.org .  Anyone who does anything MIDI is guaranteed to find a project they want there.  :grin:

Let me know what you need and I'll try to help!

Best!

SmashTV


 

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