On Tue, 10 Mar 1998 08:14:09 +0100 Morgan Olsson writes: >At 12:54 1998-03-09 -0500, Mike Keitz wrote: >>>I have seen a integrated solution using a 1 bit delta-sigma and >>>256Kbit >>>dynamic RAM. > >Texas Instruments TMS3477 >28pin DIP, using external DRAMs, max 6x1Mb >50s recording @ 2Mb 16kHz. OK, I knew some like these were out there. The one in the answering machine I took apart was a Toshiba, connected to what looked like a single 4M-bit DRAM. The quality is kind of rough, but it does store more than 4 minutes. I was interested in using ordinary parts (except the PIC, which I suppose is common enough to consider an "ordinary part" now) and more concerned with audio quality than bit rate. > >But DRAM is no good for battery backup since they draw some current. They don't use a lot of current, about 200 uA per chip in the minimum "keep alive" refresh mode using a low-power chip. The ordinary chips are still under 1 mA. This is too much to use a little lithium battery on, but a 9V or 4 AA cells can provide days to weeks of backup power. Most of the commercial answering machines take this approach. Since the customer buys the batteries seperately, they don't increase the price of the machine. Usually the only specification provided is at maximum operating speed. DRAM chips are like most CMOS, they use less power as the speed decreases down to almost zero. Running only refresh cycles is rather slow. My audio delay project uses 10 mA total at 5V in full operation, I measured the DRAM using about 3.5 mA of that, probably the PIC (16C84 @ 10 MHz) uses another 2 mA, and the rest goes to the analog stuff. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]