Author Topic: 8-bit FIFO-based flanger/chorus  (Read 5211 times)

earthtonesaudio

8-bit FIFO-based flanger/chorus
« on: February 14, 2009, 12:26:53 AM »
Here's what I want to make:

Analog in>8-bit flash ADC>big FIFO (clocked by 4047/LFO controls frequency)>8-bit MDAC>analog out.

Basically this would be like an 8-bit version of the analog bucket brigade delay.
I want to stick to technologies that I can understand, hence the flash ADC/MDAC and FIFO.  I DON'T want to use a microcontroller, and if everything can be in a DIP package, that's a plus (hard to breadboard SOIC or PLCC packages!).  The simpler the control logic is, the better.

I get stuck when it comes down to making sure the read/write/enable/reset/etc. pins are taken care of.  Thanks!

-Alex

slacker

Re: 8-bit FIFO-based flanger/chorus
« Reply #1 on: February 14, 2009, 06:22:14 AM »
I can probably give you a hand figuring out the logic for the FIFO, but I've never done anything with with ADC/DAC other than making a Nyquist aliaser using an ADC0804.

oskar

Re: 8-bit FIFO-based flanger/chorus
« Reply #2 on: February 14, 2009, 09:00:56 AM »
I'd be glad to offer my help too. The conversion shouldn't provide any bigger difficulties.
I've used this one with good result. DIP, high speed and easy to set up with parallel inputs and not a lot of controls. Basically you just
pull the /WR pin16. Pin 6 and 15 tied to ground. I think you could use an R/2R ladder too.

For fast data accusition you can use a flash converter, yes, but there are many SAR based ADC's that will do the job fast enough for your needs.

earthtonesaudio

Re: 8-bit FIFO-based flanger/chorus
« Reply #3 on: February 16, 2009, 10:51:07 AM »
Thanks guys.  Coincidentally I was already looking at the same chip family as the one Oskar linked to.   8)

My two main requirements for this project are: have to understand the theory of operation of all the basic parts; and everything has to be in DIP format (breadboard friendly).

I'm okay with using a SAR now that I feel I understand them a bit better.
A problem I've run into is finding large FIFOs in DIP packages.  It seems these are mostly obsolete or only available in TQFP or PLCC-type packages.  For this reason I'm wondering if it would be possible to use a SRAM or other more common memory device for the same sort of application.


I'll probably start ordering some chip samples soon.

oskar

Re: 8-bit FIFO-based flanger/chorus
« Reply #4 on: February 17, 2009, 01:41:01 PM »
Yes. It probably is the same amount of thinking needed for that job and I was going to suggest it. There are also adapters from surface mount to dip and I or someone else with surface mount experience can probably help you if needed. But actually an ordinary SRAM is best, also because you'll need to learn how to adress a memmory anyway sooner or later.

earthtonesaudio

Re: 8-bit FIFO-based flanger/chorus
« Reply #5 on: February 18, 2009, 07:20:59 AM »
Yep.  I was thinking SRAM is the way to go.  I don't really have a problem with surface mount components when it comes to soldering but for prototyping obviously something that's breadboard-ready is easier.

Now the big question, where do I go to learn how to address a memory?

oskar

Re: 8-bit FIFO-based flanger/chorus
« Reply #6 on: February 18, 2009, 08:54:04 AM »

earthtonesaudio

Re: 8-bit FIFO-based flanger/chorus
« Reply #7 on: February 18, 2009, 01:13:05 PM »
Thanks!

earthtonesaudio

Re: 8-bit FIFO-based flanger/chorus
« Reply #8 on: February 18, 2009, 03:48:55 PM »
Found a couple large FIFO's that are affordable:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=800-1490-5-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-4464-5-ND

I think both of these are available in PLCC packages, which are pretty easy to find sockets for.