Homebuild Function Generator ..... HELP

[IanP]

dds generator homebuilt

Converting square wave to sine wave in a wide range of frequecies is not a straightforward excercise ..
In you function generator you also generate triangle wave, which can be converted to a sine wave using breakpoint shaping network .. see picture below ..
Maybe you can employ that concept ..
Regards,
IanP

 

[jonw0224]

icl8038 function generator,schematic

I've attached a schematic and an explanation for picking the resistors or expanding the design.

Pick a couple of points on the sinewave:

sin(0) = 0
sin(30) = 0.5, relative slope from 0 to 0.5 is 0.5
sin(60) = 0.867, relative slope from 0.5 to 0.867 is 0.367
sin(90) = 1, relative slope from 0.867 to 1 is 0.133

Choose R1 and R2 so that gain of circuit is 0.5 with all diodes open
Choose R1 and R2||R3 so that gain is 0.367 with R3 diode shorted
Choose R1 and R2||R3||R4 so that gain is 0.133 with R3 and R4 diode shorted
Choose V1 = 0.5, V2 = 0.867. You can use resistor dividers to get V1 and V2 as long as the resistances in the divider are at least 10 times lower than R2, R3, and R4. Add a 3 volt triangle wave to the input and you'll see an approximate 1V sinewave at the output. For, more precision use more points on the sinewave. This should be more than enough information to get you started on your own design.