tag:blogger.com,1999:blog-8782724.post-19319642051385914092008-05-02T13:09:00.000+05:302008-05-02T13:09:00.844+05:30 <ul> <li>CMOS gates and Opamps have a output drive capability of ~ 10-20mA, so when you drive a load say an LED use a series resistor to limit the current to 5mA to 10mA.</li> <li>In a industrial environment many motors, DC drives and AC drives will be running, this will produce EMI, RFI, kickback spikes which cause microcontroller based equipment to hang. Use a watchdog timer for uC, opto couplers for all input and outputs, 4-20mA current signals for input and output, and a isolated wide range SMPS as power supply. more care is needed now as mobile phones and transmitters are filling the air with a lot of RF. so design circuits with care.</li> <li>When you measure DC levels in 16bit accuracy or more you need resistors which have temp. coeff. of 10ppm, or you may have to put the entire circuit in a stable 45 deg oven. Thermoelectric effects, EMI, RFI, pA Leakage currents, ground loops, contact resistance all can make the readings drift and unusable.</li> <li>When the number of digital chips you use in a project goes above 20 or 30 then it is better to use PLD or CPLD types from <a href="http://www.altera.com/">Altera</a>, <a href="http://www.xilinx.com/">Xilinx</a> or <a href="http://www.latticesemi.com/">Lattice</a> etc.. But when high speed is not required and for simplicity use microcontrollers.</li> <li>A battery that can be charged is best charged in CC constant current and CV constant voltage modes, that means both current and voltage have to be limited. When a battery is deep discharged many times it will age fast, and an empty battery will take huge currents so limit current. overcharging a battery will kill it so after a voltage level is reached it should only trickle charge in mA and a battery has to be cut off on overload or before deep discharge</li> <li>Look at this page on electromagnetic spectrum which will tell you about light and frequencies <a href="http://en.wikipedia.org/wiki/Electromagnetic_spectrum">see at wikipedia.</a></li> </ul> delabshttp://www.blogger.com/profile/13912180441358913305delabs@yahoo.com