At 10:52 PM 10/5/99 -0400, you wrote: >Hi All, > >I am beginning a project for school in which I must interface a micro >(maybe a PIC, haven't decided yet ;-) to both accelerometers and piezo rate >gyros (its an autonomous helicopter project). > >I need a little bit of help in interpreting the datasheets. First off, it >appears that most rate gyros give a constant DC output for a constant roll >rate, and the accels give a constant DC output for a constant acceleration. >Correct? > >Secondly, aparently, for both gyros and accels., there is a large >manufacturing variation in the DC offset. So, I guess we are just supposed >to calibrate them to find out what the offset is and subtract it out? It >may seem obvious that this is the answer, but I found it strange that the >offset can sometimes be 500 times the DC level that would represent a >typical slow roll rate! > >In addition, there seems to sometimes be a fairly sizeable tempco on the >output. How often does one need to compensate for this? In other words, >should I expect to have to include a thermistor in my circuit if I want to >detect,say, 0.1 g or 0.5 deg/sec roll rate? OR, should I be looking for >better gyros/accels that have a smaller tempco? Just packed 4 accels and signal conditioners, a few strain gage conditioners, and a rate gyro conditioner into 2 cubic inches--along with two PIC's, 512 KB of sRAM, and a serial interface. AND it survives 500 G impacts just fine while logging 8 channels at several hundred scans per second. As far as the sensor outputs--depends on the sensors! Some need excitation/power and a differential input instrumentation amp. DC offset does indeed wander all over the map. You've already spotted the temperature drifts too--particularly machined silicon Accels. Give me a little more information on your sensors, and I'll see what I can suggest--preferably off list--unless a lot of other folks are interested. kelly William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems & San Diego, California, USA