[sdiy] Arpeggiator1 / Arduino UNO

[Rick Jansen]

> On 12 Apr 2015, at 09:16, Nantonos <nantonos at epona.net> wrote:
> 
> 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.

You're right, I checked the datasheet, they call the LSB bit 8, so I was wrong. I wondered already whether they made a mistake. There is no board for this circuit, so you never know. 



> 
>> 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.

They tell you to build it with 1% resistors, or better if you can find them. So, no substrate or trimming here. Not sure if it is good enough for control voltages.

r.

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