- 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.
- 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.
- 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.
- 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 Altera, Xilinx or Lattice etc.. But when high speed is not required and for simplicity use microcontrollers.
- 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
- Look at this page on electromagnetic spectrum which will tell you about light and frequencies see at wikipedia.
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