Hi Brendan, Why not use a PIC with a built-in comparator or ADC? If you run it slow enough or allow it to sleep when there is no motion, that should work very well. Sean On Sun, Aug 10, 2008 at 5:16 PM, Brendan Moran wrote: > Hi, > I'm looking for a solution to monitoring three analog voltages from an accelerometer. I need to be able to set two threshold levels for each voltage. The total power budget for the voltage monitor is about 1mA @ 3.3V. I need to set the threshold levels through SPI or I2C. I need to be able to read the voltage levels once a threshold level is tripped. The measurements are outside of the 1mA power budget since they're only for while the system is in motion. > > I'm building a position tracking system. I have a sensor which reports a very accurate position delta, but it has two failings: it's power hungry and it's got nasty latency waking up from sleep (as bad as 2 seconds) after waking up from sleep mode. This will be a battery powered sensor package, so power consumption when idle is an issue. > > My current solution is to use a MAX1363, which will do both the monitoring and the level reading. I'm limited to 400kbps I2C, which means I have a maximum of 33ksps, divided over 3 channels, not including I2C overhead, which leaves me with about 10ksps per axis. > > I think that 10ksps should more than do the job since the tracking system should see movement not exceeding 5Hz, with peak acceleration of no more than 5g (peak should usually be around 2.5g) , RMS acceleration closer to 0.5g. The sensor I've picked has four selectable G levels from +/-2.5G to +/-10G which should make that range easy to work with: MMA7261QT. To get position delta, I plan to do a discrete double integral of the acceleration and set a zero point every time that my other sensor reports no motion. > > So, is there a better solution for my application than the MAX1363 + MMA7261QT? Together they take 1mA @ 3.3V, which is within my power budget. > > Thanks, > Brendan > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist