pic microcontroller based input switching for spin semi fv1

[differo]

I'm trying to get this type of switching to work. Still in the beginning of it all, setting up the board and the debugger (icd2), there was long time ago I fiddled with these things. But it's coming back. Anyways, I'm pretty sure that someone (or many?) have succeeded in this task, I was able to find some finished stuff in this part of the forum but no hint nor explanations how it was done. So, what I want to do?

Control s0-s2 pins of the Spin semi FV1 in order to switch between the different effects and even the switch for external effects. This is to be controlled from pic (I have 16f877a at hand with the crystal, lcd and other stuff needed). Pic is controlled simply with two momentary switches that increment up/down and translate that to binary coded output for switching fv-1. However, in the datasheet it says that this pic (whole series actually) can operate with supplied 2-5V but I also find reports that it wont work under 4V. Because FV1 work on 3.3V one option is to drive the pic on the same rail and when I output high on one pi I would get 3.3V which will be perfect for switching. What I want to prepare if this won't buzz, is somehow using the 5V output to control the 3.3Vaccepting fv1. Open collector pins? Supposedly RA4 pin is on but I need at least 3 (or 4) that I can pull up to 3.3V with a resistor and use that. Anyone know more on this= Actually as it's cmos it's open drain but nevertheless.


Any other thing I could do? use transistors or simple logic or something? I mean after the output pins. In my previous builds of this I used 3 spdt switches to change the effects. My schematics is originally francisco pena's fraverb (tonepad.com) but I change it a little bit as it contains some errors. Also I added eeprom support and that was already been so much fun, cheep eeprom programmer and some sample code it's really wicked - changing the programs and effect like that it's surreal  
Any ideas? I hope i wasn't to unclear what I want to do.

[JKowalski]

Why don't you just use a voltage divider...?

Sometimes the simplest answers are the hardest think think of.

[Gurner]

The way Id approach this is as JKowalski says, but here is a bit more meat on the bones...


Two resistors ...the junction of the resistors goes to wherever you need´switched 3.3V ....the lower part of this chain goes to ground (0V), the upper part of this chain goes to your PIC PIN.

when you want 3.3V at the junction of your resistor divider chain, switch the PIC pin high ....this puts 5V on the top of the potential divider & you have already got 0V on the bottom - just a matter of selecting the right resistor values to get 3.3V out ( http://www.electronics2000.co.uk/calc/potential-divider-calculator.php ), when you want 0V at the junction of your potential divider, switch the PIC PIN low.´...this puts 0V at both sides of your potential divider, therefore the junction will be 0V too.

[differo]

well, this sounds like a good idea! thanks Jkovalski and Gurner! true that simple things are often missed when you sit and try to design stuff like this, it was six years since I did any pic project but last night I got my head out of my a** and dusted off my good old icd2 debugger and actually breadboarded simple circuit that I'm gonna need for this, connections are working I can debug (after a lot of trial and error - fantastic how easy you forget stuff). I'll try this tonight!

[PRR]

> I also find reports that it wont work under 4V.

Datasheet says it needs 4.0V to run at 20MHz but under 4MHz it should work at 2V.

Since we used to do multi-user interactive word processors on 1MHz machines, you should be able to read two switches and toggle two pins with 4MHz and 3.3V.

[aresaudio]

Check this page:
http://www.aresaudio.com/stomp-reverb.html
There are simple switching programs

Regards