Hi,

I am building a function generator. The output functions (sine/traingle/square) all have amplitude 5V(thus 10Vpp). This is the maximum required output amplitude.
I want to use a PIC to digitally attenuate the signal. Does anyone have any circuit ideas? Digital Pots with the required voltage ranges are quite expensive where I live and have only a maximum resolution of 8bits. I have seen circuits using 12bit DAC's, however, again these DAC's with +-5V support are expensive.

maybe I can scale the signal first, then attenuate/amplify and scale again? this would probably create noise though....

thanks

 

Think about using the PIC's push-pull IO. You can use the IO ports to sink current for resistors on a voltage divider. If you had a 1k resistor on the attenuator output, and then resistors of some form (perhaps in powers of two) you could control the divider and attenuate the signal.

 

Thanks for the reply...
I bought the DAC0832 D/A converter... apparently it can act as an attenuator. However, I am struggling with the output.
To test the DAC I connected it exactly as in figure 7 (in datasheet), using LF347 opamps with +-12V rails, and I gave it a +5V reference voltage.
All digital inputs are tied to +5V and I made sure that all other digital connections are correct, adding a button to WR1 to write the input values to the DAC register.
I expected the ouput to be ~5V, but the output of the opamp was at the negative rail (-12V). I changed the reference, the digital values etc, to no avail...output stays at -12V.
It seems like the feedback is not working.. I don't know..is it the LF347 opamp?
Can anybody suggest an opamp I should use or point out where I am going wrong?

Thanks

 

Also, does anyone know where to find a multisim/pspice model for DAC0832?