Homebrew Digital Effects Pedal

Step 2 Materials

I used a number of ICs in the construction of this project, they are listed below.

  - PIC16F877a with 20MHz oscillator
  - 23k256 RAM operating at 20MHz, interfaced via three-wire SPI
  - A standard 9V single throw relay (though I recommend double throw, they are more useful)
  - IRFD120 N-channel MOSFET for powering the relay
  - LM358 operational amplifier
  - 1 Mohm trim pot (for mixing ADC and unprocessed guitar when the pedal is not in "kill" mode)
  - a bunch of 10k and 20k ohm resistors for the DAC
  - 4 switches
  - Aluminum enclosure
  - Two LEDs
  - 3 10k potentiometers
  - lots and lots of stranded-core wire
   - Guitar audio jacks
  - Barrel plug socket for DC adapter

Resistances and capacitances are generally labeled on the schematic in the next step.

Comments

[lufox15]

Great Work! i have a question which is the sample time that you can get with the pic16f877?.
I was trying to make a similar project but i can only get a maximun sample time of 625Hz.
Thanks.

[hanley]

hey, looks great
What kind of DAC do you use?

[colin353]

I used the most primitive DAC ever: a resistor ladder! It works great though, suprisingly.
 
Take a look at Step 5 under the DAC section for a link to the schematic I used, or refer to my notes in Step 7 for a poorly-drawn schematic that I put in my notes.

[Pieter-Jan5000]

 Hello, I started working on a project like this a few weeks ago. How did you put your PIC ADC into 8-bit mode? Or did you just leave out the last two bits of the 10 bit conversion?   

And how did you write the code so that the playback frequency was exacly the same as the recording frequency?

Thanks!! Awesome stuff

[colin353]

There is a flag I passed to CCS (the compiler I wrote my code for) which converts it to 8-bit mode, though you could indeed just ignore the last couple bits. My code is attached somewhere, I believe, you could read it if you want.

I got the playback and recording frequencies synchronized by the use of interrupts and calibration, essentially. Again, read the code if you want an example of how I did it (though I am very confident there are smarter ways of doing it)

[jgbrownlow]

Awesome work!  I am amazed you (or anyone) had the patience for all the point to point soldering (and got it to WORK!).
Any chance for a full, clear schematic (Eagle, MS Paint, etc), including part values? 

[colin353]

http://www.flickr.com/photos/colin353/4385411009/

Contained here are my hand drawn schematics photographed in high quality.

I feel however that this project is not one to be copied, because it is too complicated to try to create, debug, etc without already being able to design it, you know? I would use this instructable as more of a suggestion on how a project could be designed- a list of successful techniques in homebrew digital audio electronics.

Don't get me wrong though, feel free to try and copy it if you are brave enough :P