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Advertising Index Altronics.................................. 72-75 Amateur Scientist CD................... 63 Bitscope......................................... 9 Electronex...................................... 5 Emona Instruments...................... 45 Futurlec.......................................... 6 Geoff Coppa............................... 103 Grantronics................................. 103 Hare & Forbes.......................... OBC Ask SILICON CHIP . . . continued from p102 viously you can’t measure the SPDIF frequency directly as the clock and data are encoded on the one signal and would vary, depending on the data. (S. G., Carnegie, Vic). • You are right; computers will often down-sample the audio to 44.1kHz/ 48kHz 16-bit for various reasons. The main one is so that several applications can play sounds simultaneously and these are mixed in software, at a fixed sampling rate and bit depth. Some sound drivers let you set/ query this information but you can measure it at the DAC. The left/right clock is output from the LRCKO pin of IC3 (pin 10) and this is a square-wave with a frequency equal to the sampling rate. It connects to pin 10 on the digital I/O header and thence to pin 4 of IC6 (PLRCK). You can measure this with a frequency counter or scope. Unfortunately, there is no easy point to probe this line since it runs only on the underside of the two PCBs. You could solder a short length of solidcore wire to pin 10 of one of the 16-pin IDC sockets and have it stick out from under the board and you could then measure the frequency, relative to a convenient ground point such as a regulator tab or power supply ground terminal block screw. This short length of wire should not interfere with the operation as long as it doesn’t short to anything. There’s no easy way to tell whether your sound card is outputting data with a 16-bit or 24-bit resolution. You can connect an oscilloscope or logic probe to the serial audio bus and monitor the serial clock and data 104  Silicon Chip DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305 Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au High Profile Communications..... 103 Instant PCBs.............................. 103 Jaycar .............................. IFC,49-56 Keith Rippon............................... 103 Kitstop............................................ 6 LED Sales.................................. 103 Notes & Errata Crystal DAC (February 2012): the trimpots were specified as 500Ω but should in fact be 5kΩ. This affects the circuit diagram, PCB overlay and parts list. Also, the labels for Q22 and Q23 are swapped on the overlay diagram (Fig.6, page 32). Crazy Cricket/Freaky Frog (June 2012): the Jaycar buzzer part number is incorrectly listed in the parts list. It should be AB-3440. Wideband Oxygen Sensor Controller (June-August 2012): the parts list in part 1 (June, p42) includes two 3.5mm stereo jack plugs. Delete these and substitute two PCB-mount 3.5mm stereo switched jack sockets. lines. There are 32 serial clock pulses per sample sent; if the audio data is 16-bit, the data line will always be zero half the time whereas if it’s 24-bit, it will be zero for eight pulses in a row, ie, 25% of the time. Finally, it may be possible to get a general idea of the sampling rate from the S/PDIF frequency, especially if you are playing a silent file. The S/PDIF frequency is typically somewhat proSC portional to the sampling rate. Low Energy Developments........ 103 Matrix Multimedia......................... 93 Microchip Technology................... 21 Mikroelektronika............................. 3 Oatley Electronics...................... IBC Ocean Controls............................ 71 Quest Electronics....................... 103 Reality Design.............................. 10 Red Button Technologies............. 11 RF Modules................................ 104 Roc-Solid...................................... 43 Sesame Electronics................... 103 Silicon Chip Binders..................... 62 Silicon Chip Bookshop................. 95 Silicon Chip Order Form............... 97 Silicon Chip Partshop................... 96 Silicon Chip Subscriptions........... 89 Siomar Battery Engineering....... 103 Splat Controls............................. 103 Tenrod Australia............................. 7 Truscotts Electronic World.......... 103 Verbatim....................................... 41 Wiltronics........................................ 8 Worldwide Elect. Components... 104 siliconchip.com.au