DOUT to CV with R-2R Ladder

Design Concepts
1

This is a resistor ladder on a Dout module that can produce Controlable Voltage that midibox sequencers can handle

 

;; DOUT 160k 
;; D7 ---o---/\/\/\---* 
;; 80.6k | 
;; D6 ---o---/\/\/\---* 
;; 40.2k | 
;; D5 ---o---/\/\/\---* 
;; 20.0k | 
;; D4 ---o---/\/\/\---* 
;; 10.0k | 
;; D3 ---o---/\/\/\---* 
;; 5.1k | 
;; D2 ---o---/\/\/\---*----CV Out-----------------------------------o ( 0v <----> +5v )
;; 220 Ohm 
;; D1 ---o---/\/\/\--------o free assignable trigger 
;; 220 Ohm 
;; D0 ---o---/\/\/\--------o another free assignable trigger

__________________________________________________________________________

 

What i wanna ask here is..

 

How can i use a shift register with a resistor ladder as that.. but with higher voltages.. i need to go from 0 to +15v

I need to use a different from 74HC595 that DOUT uses or is there another way?

I saw something similar before but i am not so sure.. maybe a TL074 can do the job like that in this image:

 

 

Regards, Tilemachos

2

Maybe this helps?

 

http://www.ucapps.de/mbhp_aout_lc.html

3

Thank you for your answer!

 

I know about Aout_LC and is really similar to that i want!

But i need something different and i am really sorry i did not explain!

 

What i wanna build is a module with with up to 8 CV channels that i will use to control the velocity on a TR-808 clone…

 

Velocity on a TR-808 is a Trigger pulse of 1ms width with voltage from +5 and +15

 

Here is my idea taken from another project.. will this work?

 

4

To get higher voltage, you need to configure the tl074 for some gain.

You do this by adding a voltage divider to the feedback loop of the op-amp.

eg. 20k between output and “-” and 10k between “-” and GND.

 

If you don’t need those pulses at the same time, this could work.

You need to feed  A and B with address bits, though. C can stay low, since you only use 4 Outputs.

5

You mean this??

 

http://www.falstad.com/circuit/e-amp-noninvert.html

6

That’s what i meant.

 

Do you need any voltages between +5 and +15, or just those two values?

If it’s just 5V and 15V, there is an easier soulution:

You could use two DOUT pins per instrument, one going directly to the trigger-in and another going to a ULN2803 or similar, so it gets amplified to 15V and then to the trigger-in.

7

Thank you very much for help me understand this!!!

 

No i need any voltages between 0 and 15 volts with as much as high resolution i can get.. but 8-bit is ok!!

Here is an example!! Thanks for your help!

 

0 volts in = 0 volts out

1 volts in = 3 volts out

3 volts in = 9 volts out

3.5 volts in = 10.5 volts out

until i go up to

5 volts in = 15 volts out

 

That’s amazing!!!

 

Regards Tilemachos

8

Is this right or i have mistakes in my schematics?? should there be a +15v supply in the op-amp or not?

 

9

This has a gain of 1.5, to get a gain of 3 2k and 1k have to be switched.

Since the op-amp will never have to put out negative voltages, you could connect its negative supply to gnd instead of -15V.

You will need a little more than +15V on the positive supply, because else the op-amp can’t reach +15V on its output.

10

Understand!

That’s cool!!

 

Thank you very very much! That’s a nice forum :hyper: :hyper: :hyper:

11

Ok man now i am sure that it will work!

The same thing i’m trying to do is used in the TR-909 circuit! You are really amazing you answered as roland did it in the past!

Take a look!

 

12

Nah, that’s just how it’s done. Nothing special.

13

Ok i made a schematic for an 8x CV OUT and i need verification.. The R-2R ladder values are 20k and 10k.

One more thing i wanna ask is.. Can i drive J19 on mbhp_core_stm32f4 to work as the J8/9 and connect more Dout and DIN chain?

 

Here is the schematic for my DOUT with DAC and op-amps to get signal up to +15V :

 

http://www.docdroid.net/ri8z/dout-cv.pdf.html

 

Regards Tilemachos