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Overdog
Guest
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 Posted:
Sun Nov 28, 2004 12:16 pm Post subject:
Re: Analog filter |
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Bjarni Juliusson <bjarni@update.uu.se> wrote in message news:<coas6g$tl0$1@Tempo.Update.UU.SE>...
| Quote: | Gareth Magennis wrote:
Try Googling for "DIY synth circuits". There are loads of people
experimenting like this and loads of diagrams and explanations too. There's
not much on the digital control side of things, but most of the circuits
you'll find are voltage controlled anyway.
Yes, I've been googling already. I think I'll just pick one of the
designs and try it out! Just as you say, I haven't found anything about
digital control, but that's important to me. How do I generate a voltage
digitally? Perhaps by a counter counting really fast and flipping a
flip-flop connected to a transistor that feeds a capacitor :-). Isn't
that how switching power supplies work? Anyway, there is naturally a
simpler way...
For the digital side I suggest you read up on Programming Microcontrollers.
The 8051 family are powerful, cheap and well supported.
Er, the 8051 has no analog outputs does it? Anyway, the digital side
isn't really a problem. I'm a computing science student and all that,
it's just the conversion of 16 bits of TTL into a voltage that I don't
know how to do.
Anyway, thanks everybody for your help! I got some pointers, and I think
I know what to do, except the digital->analog part; I'll go google.
Bjarni
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Just buy a PIC. They're made by Microchip.
PICs have built in ADCs and DACs, and onboard flash memory so you
don't have to solder an external memory chip.
Your main problems will be finding a compiler and finding a
"programmer" that will download the code to the chip.
Overdog
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Richard Crowley
Guest
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| Posted:
Sun Nov 28, 2004 5:41 pm Post subject:
Re: Analog filter |
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"Overdog" wrote ...
| Quote: | Just buy a PIC. They're made by Microchip.
PICs have built in ADCs and DACs, and onboard flash
memory so you don't have to solder an external memory
chip.
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The analog inputs and outputs in microcontroller chips
(like PICs, etc.) aren't suitable for audio, IMHO. They
are intended for industrial control kinds of functions.
There are programmable DSP chips, OTOH, that are
actually made for audio (and even video) processing.
OTOH, if the OP was actually looking for digitally-
controlled analog processing, there were chips made
for applications like 1-octave "graphic equalizer"
functions that were controlled with some popular
2-wire chip-to-chip interface protocols. these days,
though, DSP is becoming to inexpensive and easy to
use, they may not even make such hybrid bastard chips
anymore(?). |
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Dick Pierce
Guest
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| Posted:
Sun Nov 28, 2004 6:17 pm Post subject:
Re: Analog filter |
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Bjarni Juliusson <bjarni@update.uu.se> wrote in message news:<coas6g$tl0$1@Tempo.Update.UU.SE>...
| Quote: | Gareth Magennis wrote:
Try Googling for "DIY synth circuits". There are loads of people
experimenting like this and loads of diagrams and explanations too. There's
not much on the digital control side of things, but most of the circuits
you'll find are voltage controlled anyway.
Yes, I've been googling already. I think I'll just pick one of the
designs and try it out! Just as you say, I haven't found anything about
digital control, but that's important to me. How do I generate a voltage
digitally? Perhaps by a counter counting really fast and flipping a
flip-flop connected to a transistor that feeds a capacitor :-). Isn't
that how switching power supplies work? Anyway, there is naturally a
simpler way...
|
Well, how about a simple D/A converter: digital in, analog output
voltage proportional to the digital input value. 8 bit monolithic
D/A converters of sufficient quality to fit your needs can be had
for very cheap: you don't need much performance: since you're using
it as a source of control voltage and not passing audio through it,
you don't care much about speed or anything like that.
| Quote: | For the digital side I suggest you read up on Programming Microcontrollers.
The 8051 family are powerful, cheap and well supported.
Er, the 8051 has no analog outputs does it? Anyway, the digital side
isn't really a problem. I'm a computing science student and all that,
it's just the conversion of 16 bits of TTL into a voltage that I don't
know how to do.
Anyway, thanks everybody for your help! I got some pointers, and I think
I know what to do, except the digital->analog part; I'll go google.
|
Hmmm, let's figure this mystifying puzzle out. You have a DIGITAL
value that your want to CONVERT to an ANALOG signal.
Hmm... you need some sort of CONVERTER from DIGITAL TO ANALOG.
Hmm.. you need a ...
DIGITAL TO ANALOG CONVERTER!
Try looking THAT up! :-) |
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Bjarni Juliusson
Guest
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| Posted:
Sun Nov 28, 2004 6:18 pm Post subject:
Re: Analog filter |
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Dick Pierce wrote:
| Quote: | Bjarni Juliusson <bjarni@update.uu.se> wrote in message news:<coas6g$tl0$1@Tempo.Update.UU.SE>...
Well, how about a simple D/A converter: digital in, analog output
voltage proportional to the digital input value. 8 bit monolithic
D/A converters of sufficient quality to fit your needs can be had
for very cheap: you don't need much performance: since you're using
it as a source of control voltage and not passing audio through it,
you don't care much about speed or anything like that.
|
Sure, it's just me being such a noob about everything not digital. So
using a typical DAC will do the right thing then? I mean, they output a
voltage, not a current or a resistance or whatever, and suitable for the
control signals in question... sorry about being such a dope. Found
something called an R-2R network that seems to do what I want and be
easy to build. And before you say it: yes, I can also buy a DAC on a
chip, and I will if they do the right thing. I suppose there are
different kinds and it'll just say what type of output it provides.
Hmm... I may be a bit extra dopey right now due to sleep depravation :-|.
| Quote: | Hmmm, let's figure this mystifying puzzle out. You have a DIGITAL
value that your want to CONVERT to an ANALOG signal.
Hmm... you need some sort of CONVERTER from DIGITAL TO ANALOG.
Hmm.. you need a ...
DIGITAL TO ANALOG CONVERTER!
Try looking THAT up! :-)
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Yes, Dick. Good boy :-P.
Bjarni |
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Bjarni Juliusson
Guest
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| Posted:
Sun Nov 28, 2004 6:18 pm Post subject:
Re: Analog filter |
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Gareth Magennis wrote:
| Quote: | Er, the 8051 has no analog outputs does it? Anyway, the digital side isn't
really a problem. I'm a computing science student and all that, it's just
the conversion of 16 bits of TTL into a voltage that I don't know how to
do.
Yes you're right about that, but there are plenty of other microcontrollers
that do. Thre isn't much to converting 16 bits to analogue using an ADC
though. It can be as simple as writing "LDADC xx". The ADC does everything
for you.
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To clarify the digital bit: I already have a whole computer, and I am
well familiar with the purely digital aspects, including processors and
so forth. The complexity in software if I use, say, a 6502 is no
different from what it is if I use a microcontroller with the DAC built
in; instead of the LDADC I just STA to the address of the DAC. I am not
interested in any discussion of microcontrollers or of software, or just
about anything concerning the digital side of things. You can just
assume we have the 16 (in this case) bits of TTL data available at all
times, and all we need to do is output a suitable control voltage to
manipulate the filter circuit.
So, PICs are out of the question. Would it be at all feasible to build
something as simple as one op-amp, a couple of caps and resistors, and a
DAC or two for control? If I have a circuit that uses pots for control,
how can I interface that? Do I replace the pot with a DAC and a transistor?
Thanks everybody for your patient help on the matter despite my dumb
questions :-).
Bjarni |
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Gareth Magennis
Guest
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| Posted:
Mon Nov 29, 2004 11:17 am Post subject:
Re: Analog filter |
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I would find some 16 bit DAC and ADC chips and then go to the manufacturers
websites and look at the spec sheets. Some will provide application notes
which sound like the kind of thing you are really asking for. Also some
basic electronics knowledge would come in handy for when you have to build
or otherwise source power supplies and reference voltages to drive the
chips. Not forgetting input and output buffers etc.
Google some more for DAC and ADC circuits.
16 bits sounds a bit over the top for contolling a filter by the way.
| Quote: | So, PICs are out of the question. Would it be at all feasible to build
something as simple as one op-amp, a couple of caps and resistors, and a
DAC or two for control? If I have a circuit that uses pots for control,
how can I interface that? Do I replace the pot with a DAC and a
transistor?
Thanks everybody for your patient help on the matter despite my dumb
questions :-).
Bjarni |
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Bjarni Juliusson
Guest
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| Posted:
Tue Nov 30, 2004 12:20 am Post subject:
Re: Analog filter |
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Gareth Magennis wrote:
| Quote: | I would find some 16 bit DAC and ADC chips and then go to the manufacturers
websites and look at the spec sheets. Some will provide application notes
which sound like the kind of thing you are really asking for. Also some
basic electronics knowledge would come in handy for when you have to build
or otherwise source power supplies and reference voltages to drive the
chips. Not forgetting input and output buffers etc.
|
I think that I might be able to manage power supplies, but there seems
to be plenty of schematics on the web too.
| Quote: | Google some more for DAC and ADC circuits.
16 bits sounds a bit over the top for contolling a filter by the way.
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I don't doubt it. 16 bits was just an example for clarity and it's a 16
bit machine.
Thanks.
Bjarni |
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