BCD with DDS chip

Discussion in 'Electronic Design' started by Steve Jonson, Mar 28, 2007.

1. Steve JonsonGuest

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

2. Uwe BonnesGuest

Add a small microcontroller to read the BCD switches, calculate toe needed
SPI Pattern and transfer it to the DDS.

3. Spehro PefhanyGuest

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

4. MooseFETGuest

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.

5. John BarrettGuest

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)

6. mikenGuest

I'ts using binary switches, not bcd, but you could decode bcd to get
binary and input that as per the circuit on the link.

Regards MikeN

7. Spehro PefhanyGuest

Do you think that approach is feasible with a 32 bit binary output?

Best regards,
Spehro Pefhany

8. MooseFETGuest

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.