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PC-controlled 0-30kHz sinewave generator Based on the ML2036 audio generator IC, this simple project hooks up to your PC’s parallel port and generates a sinewave output from 0-30kHz. The output frequency and level are controlled via the on-screen display. By MARK ROBERTS This simple audio oscillator uses just a handful of parts and will only take about 10 minutes to assemble. It’s low in cost too (just $30), since you don’t need to buy fancy digital dis­ plays, or frequency and level controls, or an output level meter – at least not in hardware form. Instead, that’s all taken care of by the software which generates a “virtual” instrument panel on your PC’s monitor. 66  Silicon Chip Fig.1 shows what the on-screen display looks like. As can be seen, it has a digital frequency display (with up to five digits), digital and analog output level meters, and controls to set the output frequency and level. The output frequency is set by either rotating the Tuning knob (by dragging it with the mouse) or by clicking the up and down buttons to change the reading in 1Hz, 10Hz or 100Hz steps. You can also change the output frequency by clicking at any point on the circumference of the Tuning knob. When you do this, the red dot on the tuning knob jumps to the new setting and the display changes accordingly. The signal level can be varied from 0-4V in 10mV steps by clicking another pair of up/down buttons. Alternatively, for more rapid changes in output level, you can drag the slider bar bet­ween these two buttons. The accompanying 3-digit display shows the output level (in Vp-p), or you can read the level off the analog meter. Immediately to the right of the output level control are three other buttons. The top button (shown as 100Hz in Fig.1) lets you toggle between 1Hz, 10Hz and 100Hz frequency steps. The middle button is labelled “Help” but no help functions were available at Fig.1: the sinewave generator is controlled via this virtual instrument panel which is generated by the software. Specifications Frequency Range: 0-30kHz sinewave Frequency Steps: 1Hz, 10Hz & 100Hz Output Level: 0-4Vp-p (.01V steps) Frequency Response: flat from 0-30kHz Total Harmonic Distortion: less than 0.5% from 2Hz to 30kHz <at> 1.066V RMS the time of writing. The third button, labelled Exit, shuts down the program. There are also three memory channels, situated immediately to the right of the analog level meter. You can program three spot frequencies (eg, 1kHz, 10kHz and 20kHz) into these channels, each with a different output level if so desired. Programming is easy – you simply click a memory button, set the frequency and output level, and then click the R/W button (below the memory buttons). Performance Figs.4 & 5 show the performance details. As shown in Fig.5, the total harmonic distortion at 1V RMS is less than 0.5% over the frequency range Fig.2: the circuit is based on IC2 which is an ML2036 sinewave generator. It’s output frequency is set by the voltage applied to its VREF input from IC1, a 10-bit digital-to-analog converter. The output from IC1, in turn, depends on the data applied to it via the parallel port of the computer. April 1998  67 from 20Hz to 30kHz and is generally less than 0.2% above 1kHz. We also checked the output level as a function of output frequency. It’s dead flat, with 0dB variation over the full frequency range. Power for the circuit is derived directly from the parallel port, so no external power supply is required. A +5V rail is derived from pin 9 of the parallel port and this is fed to pins 13 and 8 of IC1 and IC2, respectively. In addition, the +5V rail is fed to pin 8 of IC4, a 7660 switched-capacitor inverter. This device produces a -5V rail at its pin 5 output and this is fed to pins 1 & 2 of IC2. Circuit details Fig.2 shows the circuit details. It’s based mainly on IC2 which is a Micro Linear ML2036 programmable sine­ wave generator capable of producing frequencies from 0-50kHz (only 0-30kHz used here). In this circuit, IC2 is controlled by a 3-wire input from the parallel port, the signals being applied to pin 5 (SCK – serial clock), pin 6 (SID – serial data input) and pin 7 (LATI – latch input). IC2’s output frequency is programmed by a 16-bit serial data word which is applied, via the parallel port, to pin 6 (SID). An 8.388MHz crystal between pin 14 and ground provides the internal clock signal and sets the upper frequency output to 30kHz. The output level is set by the voltage applied to pin 9 (VREF) of IC2 and this in turn is set by IC1, a MAX504 10-bit digital-to-analog converter (DAC). The serial data generated by the software is fed into pin 2 (DIN), while SCLK and CS-bar are the clock and chip select inputs, respectively. The converted analog output voltage appears at pin 12 (VOUT). IC3 is a Dallas Semiconductor DS2401 “Silicon Serial Number”. This 3-pin device comes in a standard TO92 package but only two of its pins (ie, Data and GND) are used. Each one of these devices comes with a unique 64-bit regis­ tration number and this Construction Fig.3: install the parts on the PC board as shown on this wiring diagram. number is read by the software (via pin 15 of the parallel port). If the number matches the number pro­grammed into the software, the software functions normally. Conversely, if the numbers don’t match, the software still boots but goes into a demonstration mode only. This means that the software supplied with each individual DS2401 is tailored to match that device. The same software will not work with other devices because the code number will be different. All the parts, including the BNC output socket and the DB25 connector, are installed on a PC board measuring 77 x 55mm. Fig.3 shows the assembly details. Begin the assembly by installing the three wire links, then install the resistors and capacitors. This done, install the three ICs and the 8MHz crystal. Take care to ensure that the three ICs are correctly oriented (they all face in the same direction) and don’t get the MAX504 mixed up with the ML2036. Finally, complete the assembly by fitting the BNC socket and the DB25M connector. Check that both these devices lie flat against the PC board before soldering any of their pins. Go over your work and check carefully for mistakes before connecting the unit to a computer, ready for testing. You can either plug the unit directly into the parallel port or connect it via a DB25 male-to-female cable. Installing the software The software comes on three floppy discs and runs under Windows 3.1x, Windows 95 and Windows NT. You install it by run­ning setup.exe on the Where To Buy Parts Parts for this design are available from Softmark, PO Box 1609, Hornsby, NSW 2077 (phone/fax 02 9482 1565). ML2036 programmable sinewave generator ...............$18 MAX504 10-bit digital-to-analog converter ....................$9 ICL7660 voltage converter ............................................$4 8.388608MHz crystal ....................................................$3 PC board .....................................................................$10 BNC and DB25M connectors ........................................$7 Software (three discs) with DS-2401 ..........................$32 Optional LPT2 card .....................................................$15 Fig.4: this scope shot shows the residual hash at the output of the generator, as well as the distortion. The upper wave­-form shows the output signal at 1kHz. 68  Silicon Chip Payment by cheque or money order only. Please add $5 for postage. Note: the software associated with this design is copyright to Softmark. AUDIO PRECISION ext 5 THD+N(%) vs FREQ(Hz) P.C.B. Makers ! 18 FEB 98 16:07:21 If you need: •  P.C.B. High Speed Drill •  P.C.B. Guillotine •  P.C.B. Material – Negative or 1 Positive acting •  Light Box – Single or Double Sided – Large or Small •  Etch Tank – Bubble or Circulating 0.1 – Large or Small •  U.V. Sensitive film for Negatives •  Electronic Components and 0.010 •  •  0.001 20 100 1k 10k 30k Fig.5: this graph shows the total harmonic distortion of the generator over the range from 20Hz to 30kHz. first disc and following the on-screen instructions. In Windows 95, you click Start, Run and then type A:\setup. exe in the space provided (assuming that the floppy disc is in the A: drive). The installer program creates the appropriate program group and installs a shortcut in the Start menu. In Windows 3.1x, you click File, Run and type A:\setup.exe. Alternatively, you can double-click the setup.exe file from within File Manager or, in Windows 95, from the Explorer. When you boot the software, it opens a dialog box that lets you select between two printer ports (LPT1 and LPT2). LPT2 is the initial default but most users will need to select LPT1. You then click OK to bring up the instrument panel shown in Fig.1. Ini­ tially, all the displays will be off, since the Power is off. You turn the display on by clicking the Power button. By the way, once you’ve selected a port, the software always boots up with the new port as the default, unless you change it again. It’s now just a matter of checking that everything works. Check that you can vary the output frequency and level and that all the other “controls” work correctly. The default frequencies programmed into the memory buttons are 1kHz, 2kHz & 3kHz. The output of the oscillator is best Parts List 1 PC board, 77 x 55mm 1 PC-mount DB25M connector 1 PC-mount BNC connector 1 3-disc software package Semiconductors 1 MAX504 10-bit DAC (IC1) 1 ML2036 programmable sinewave generator (IC2) 1 DS2401 silicon serial number (IC3) 1 ICL7660 switched capacitor inverter (IC4) 1 8.388608MHz crystal (X1) Equipment for TAFEs, Colleges and Schools FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE Prompt and Economical Delivery KALEX 40 Wallis Ave E. Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 •  ALL MAJOR CREDIT CARDS ACCEPTED Silicon Chip Binders REAL VALUE AT $12.95 PLUS P &P Capacitors 1 100µF 16VW PC electrolytic 5 10µF 16VW PC electrolytic 1 0.1µF monolithic Resistors (0.25W, 5%) 1 1kΩ 1 200Ω checked on a scope. If you don’t have a scope, feed the signal into an audio amplifier and listen while the unit is swept over the frequency range. Of course, you won’t be able to hear anything much above about 15kHz, depending on your hearing and the loudspeaker used, but this is still a good check that the unit is working. SC ★  Heavy board covers with 2-tone green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5 p&p each (Australia only) Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. April 1998  69