I am interested in using something like the AD9851 DDS chip to generate audio sinewaves but controlling it with BCD swtiches instead of a serial input. IOW I need it to be independent of a computer or micro. Can anyone advise where I can find the information to do this, or provide a summary of the technique?
Regards,
Steve Jonson
Add a small microcontroller to read the BCD switches, calculate toe needed SPI Pattern and transfer it to the DDS.
Almost certainly the sensible answer is to use a micro, though there could be some situations where an FPGA might make sense. The math you need, including a 32-bit BCD->binary conversion is not very convenient for discrete logic.
Best regards, Spehro Pefhany
How good does it have to be? It may be easier to make a DDS circuit that runs in BCD than to convert for the AD9851. This would be much more likely if you only need one or two digits and can stand some distortion.
If you must convert BCD to binary and need to avoid all programable parts, you may be best off using programable BCD counters to control how many pulses go into a binary counter.
gonna take you far more in the way of discrete logic than it would with an MCU -- you can get the entire functionality needed in an 18 pin dip and a one-of-8 decoder (to select the BCD switch for reading)
Have a look at
Regards MikeN
Do you think that approach is feasible with a 32 bit binary output?
Best regards, Spehro Pefhany
Yes, for very small values of feasible. 7 Minutes isn't that long of a time.
I wasn't, however, thinking of numbers that long. 6 digits would be quite reasonable and since the oscillator this is driven from is likely less accurate than that, this is likely to be enough.
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