[sdiy] Arpeggiator1 / Arduino UNO

[Nantonos]

Hello Rick,

Saturday, April 11, 2015, 3:45:29 PM, you wrote:

> The Elektor Formant book2 has a digital keyboard schematic, where a
> key pressed results in a 6-bit value, derived using priority encoder
> chips (74LS148):

> <http://dropmix.xs4all.nl/rick/Emusic/Arpeggiator1/img/formant2_CV_DAC.jpg>

> here they use a ZN426 8-bit DAC, of which they use the lower 6 bits
> to generate the output voltage.

No, they use the upper 6 bits. Look at the pinout in the datasheet;
Bit 1 is annotated (MSB) and Bit 8, unused in this schematic, is
marked (LSB). Thus they retain the specified INL.

Using the lower 6 bits as you suggest would have two effects: the
maximum output voltage would be 1/4 the value (instead of 2.55V +/-
75mV, it would be 360mV) and the INL would be 4 times worse.

> The next page has a schematic for a classic R-2R circuit, but if
> that is really a practical circuit I don't know.

It is practical as long as you work out what the tolerances are for
each resistor. Even 20 years ago, that keeping them on the same
substrate and quite likely, on-chip trimming.



-- 
Best regards,
 Nantonos                            mailto:nantonos at epona.net