Midi to CV -> ZN426 DAC ?

[Verheyden Tom]

At 04:19 4/02/97 +0100, you wrote:
>
>I want to finally make up the Elektor/Doepfer midi to cv project.  It
>specifies a ZN426 DAC that is apparently made by Ferranti and QEC
>Plessey.  I have so far been unable to locate a data sheet on the DAC.
>Is there another you guys might recommend that is more readily
>available?  The ZN426 apparently has an onboard voltage reference
>but needs a negative voltage supply and an external op amp to
>achieve 0-5V range. 

The negative voltage-thing is not really a problem. The elektor-engineers
have done a real good job by designing this project. The negative voltage is
substracted from....... the ALE signal from the µ-controller!!!!!!
This signal will be multiplied (diode-cap-network, in circuit diagram:
C5,C6,D3,D4) and then rectified (even made negative) to a -3V DC-voltage.
Ofcourse you can't get many mA from this voltage but it's just enough to
feed the ZN & the opamp. Watch out if you want to replace the opamp by
another type, the bias-current must be simmilar to the original opamp TL061
(so NO: TL071/081 or 741's please!). 

If you want to build a MCV1, watch out for the bugs!! The resistor-values in
MIDI-in and MIDI-out are messed up on the PCB. I believe that there is an
updated version of the MCV-1, but in my case, I had some
unbelieveble-bug-search-hours !

Oh yeah, the tuning is a bit complex, it's not just switch power and jam,
first press mid-c and tune, then press high-c and adjust, then press low-c
and try to adjust a little more.


 I've found cheap 8 bit DACs (not pin compatible)
>that can get the voltage range but need the voltage reference.  I
>imagine there are solutions from Maxim etc. that have on board
>reference and the range, I just don't want to use a $8+ part.
>
>Or is there a popular 8051 variant that has a DAC output?

ehmmmmm..... don't use other types than 8051 or 8031 in this circuit. If you
use a CMOS version 80c51, the whole thing just don't work. Make sure that
the ALE-signal can drive the ZN426 and TL061
>klein_b at a1.wdc.com
>
Tom,

>
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*                                                      *
* Da funk back to the punk  -------        Daft Punk   *
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* Tom Verheyden                 at KHK Geel Belgium.   *
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