mjwingrove@wateng.UUCP (Mike Wingrove) (02/12/86)
Well I seem to be having some trouble posting, but I'll try one more time.
Does anybody know of an integrated circuit (MPU peripheral chip) that can be
programmed to generate a sinusoidal waveform at a frequency determined by the
contents of a register. A computer game (or micro computer) music chip might
do. It should have two voices, but if not I can always use two of the chips.
Thanks in advance,
Mike Wingrove
University of Waterloo
UUCP: {allegra,ihnp4,decvax,utzoo,clyde}!watmath!wateng!mjwingroverdp@teddy.UUCP (02/12/86)
In article <2936@wateng.UUCP> mjwingrove@wateng.UUCP (Mike Wingrove) writes: > >Well I seem to be having some trouble posting, but I'll try one more time. > >Does anybody know of an integrated circuit (MPU peripheral chip) that can be >programmed to generate a sinusoidal waveform at a frequency determined by the >contents of a register. A computer game (or micro computer) music chip might >do. It should have two voices, but if not I can always use two of the chips. > About 3 years ago there was an article in one of the radio-electronics rags describing such an oscillator. The design was fairly simple. Basically, it consisted of two phase-locked loops. The first, acting as a frequency synthesizer, sonsisted of a 1 Hz crystal-controlled reference oscillator. This was fed into the reference input of the loop. The loop itself consisted of a CMOS phase-detector-VCO and the loop was closed by a CMOS programmable divider. The result was that the VCO output was divided by the divider, and the VCO was forced to track until the output of the divider locked with the reference. Bingo, out of the VCO comes a signal whose frequency is equal to the reference (1 Hz) times the value loaded into the divider. This part had a range of 1 Hz to 20 Khz in 1 Hz steps. The second loop consisted of an EXAR function generator/VCO in a loop that was locked to the output of the first loop. The output here consisted of a sine, square or triangle wave of the appropriate frequency. I have modified the circuit somewhat so that the oscillator has a range of 1 to 32767 Hz, and a programmable attenuator, and packaged the whole thing to talk to either a normal parallel port or directly to a DEC Qbus interface. I believe the magazine was the Feb or March 1983 issue of Radio Electronics. Dick Pierce