[sdiy] PIC628 MIDI2CV interface -site updt

[Marc Bareille]

Hello Jezz 

> do you plan on releasing the source code for your MIDI-CV convertor at all?

If there is a real interest to make it open source, why not ... but i
doubt... 

> The only reason I ask as I would like to make modifications to the circuit
> and code. I'm after a MIDI-CV with a velocity CV output (as well as pitch
> and mod CVs) and accent and slide triggers as well. I can see how to
> possibly mod your circuit to do something like this. RB2 appears unused and
> could be used along with RA3 and a bit more external logic to control a
> third output DAC for velocity and also select a latch for writing (from the
> DAC data bus) to enable more output triggers.

Well i agree with your idea. Just i have tried this before to release
the new interface. My first idea was to build a 3 CV interface, same as
my previous one ( MIDI3CV-PIC16F84), but with all the advantages of the
PIC16F628 ( usart,more Ram/flash, hi speed,cheapest) ... Also my new
MCV628 first prototype had 3DACs and a 74HC138  adress decoder to
select/write DACs with only 2 pins This method was working  well with
the PIC16F84 at 4Mhz but not with the 628 at 20Mhz. Mainly because pins
are not set exactly at the same time on the PIC pins. Any other more
conventional chip seclection method will require at least one more
pin...

Another important point : the RB2 pin is not unused at all ! Even if it
is unconnected... I have discovered this by myself ( thanks to Murphy's
law !) before reading little lines of the PIC16F628 datasheet to
confirm... When the USART is activated, the RX(rb1) and TX (rb2) pins
are reserved for serial port and cannot be used for other purposes ,
unless there is a tip i ignore to change this ...

That is why my new interface have "only" a pair of DACs. It is not
really a problem compared to my previous 3CV converter finaly, as this
interface has been originaly thinked to be integrated in vintages
"prepatched" synths and most of old devices require only a couple of CV
, one for pitch, the other one for VCF... One exception the Korg MS20
and his LP/HP filters...Anyway i will release another compatible
schematic/pcb with single PSU, ideal to transform this interface in a
standalone more universal converter. Other dvantage of this situation:
the schematics remains very simple, read "reliable and low cost" :)

I also think now that for a multi CV (>=3 but no multiplex)  interface
based on a small microcontroler , it can be interesting  to use serial
DACs. Another solution can be to use a larger PIC like the 16F876 or the
877 if you want to have 3 parallel DACs and  many trigg/gate outputs...

>
> I like the fact that the system has a learn mode and a PC based
> configuration editor as well.
>

Me too :))

Best regards,

Marc B.

PS: I have upgraded the firmware because of a hidden bug inside. The
fixed version is now v1.11P. A special version for Korg MS10/20 synth (
gate negative logic) of the firmware is available: version 1.11N. A
preliminary schematic of the single psu version of the interface is
online too at http://m.bareille.free.fr