david@epicb.UUCP (David Cook) (10/31/89)
I am looking for a CHEAP circuit which can generate a sine wave at a dialable frequency between .01 Hz and 3000 Hz with .01 hz precision. The voltage out needs to be adjustable between 5 volts and 24 volts AC (not DC). I already know about all the function generator chips available, and will probably use these... the catch is that I also need a CHEAP way of displaying the frequency, in hertz, on a LED or LCD display. I would like the entire device to cost no more than $50. I anyone knows of a chip which could take the pulse output of one of the function generator chips and display it on a LED or LCD display, and that the method is dirt cheap, please let me know. FYI.. the device is for a CES machine (cranial electro stimulation) where I hook the electrodes to my head and the waveforms sync my own brainwaves. I already have done this with a HP function generator, and it works GREAT, but I want a pocket, portable, CHEAP unit that I can take everywhere. Thanks In Advance -- uunet!epicb!david
bill@videovax.tv.tek.com (William K. McFadden) (11/02/89)
In article <856@epicb.UUCP> david@epicb.UUCP (David Cook) writes: >I am looking for a CHEAP circuit which can generate a sine wave at a >dialable frequency between .01 Hz and 3000 Hz with .01 hz precision. >The voltage out needs to be adjustable between 5 volts and 24 volts >AC (not DC). I already know about all the function generator chips >available, and will probably use these... the catch is that I also >need a CHEAP way of displaying the frequency, in hertz, on a LED or >LCD display. I would like the entire device to cost no more than $50. Probably the best way to do this is use a phase-locked loop chip. This will provide square and triangle waves. If you need sine waves, you can use the VCO of a function generator chip instead of the one in the PLL. Using phase- locked loops, you can synthesize any frequency in the VCO's range with arbitrary resolution and crystal-controlled accuracy. Some inexpensive chips to use are the 4046 for the phase detector (use phase detector 2), the 8038 for the oscillator, and the 4059 for a programmable divide-by-N counter. You can drive the 4059 using BCD thumbwheel switches. Hence, you don't even need a display. Alternatively, you could use an individual presettable divide-by-10 for each digit. The only problem I see is that with a 0.01 Hz reference frequency, settling time will be very long. (You'll have the same problem with a 0.01 Hz resolution frequency counter, too.) In college I built a frequency-synthesized FM stereo transmitter as a senior project that used a 4046, 4059, and a varactor-tuned VCO. Using the thumbwheel switches, I could tune to any frequency in the FM band with a 100 KHz resolution. My reference oscillator was a 1 MHz crystal (divided down). After zero beating the reference against WWV, I got the output frequency error below 1 KHz. I guess it worked pretty well, 'cause I got an A. If you'd like to know more about digital frequency synthesizers, send me e-mail. For the low frequencies you're using, you may also want to look into direct digital synthesis. A microcontroller driving a cheap digital-to-analog converter could produce any waveform at any frequency you want, but without the settling time of the PLL circuit. This would probably cost more than the PLL and would require some programming, but the performance can be better. -- Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077 UUCP: bill@videovax.Tek.com, {hplabs,uw-beaver,decvax}!tektronix!videovax!bill GTE: (503) 627-6920 "The biggest difference between developing a missle component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI