Voltage Requirement

hello all,

i'm making simple controller piece of machinery. i'm using 328p job. controller has inputs coming in encoder , opto sensor. opto sensor runs @ 12v , encoder runs @ 5 12v. here's annoying part, input nice 24v. tried find regulator drops 24v 5v directly, there 24v 12v drop regulators.

my question is, okay use 24 12v drop regulator, power opto sensor, use 12v coming same regulator drop down again 5v 7805 ?. method efficient, or regs burn each other ? .

also, have silly problem, when encoder or opto sensor pulse arduino, logic level high in range of 12v 24v. need drop down voltage state 5v pulses coming in, voltage divider better?, or regulator again work better ?
also, need  capacitors regulators if 24v input coming smps based supply ?
thank you

you can chain regulators that, long within spec fine (though bet somewhere in there mains current can use screw terminals wire in wall wart, do)

for 24 volt signals coming in off of sensor or whatever in machine of sort best way have found use opto-isolator , 317

an opto-isolator typically 6 pin (or multiples of) ic, inside has led, other side has photo transistor, hook higher voltage led , use 317 in series ground set current regulator not blow led. transistor side hooked between 5volts , avr's input.

you use resistor limit led current, dumping 24 volts single led , dissipating power going require decent size package, , happens if voltage changes (i have seen these things float on place depending on whats happening)

regulators bad idea cause need signifigant amount of capacitance keep them steady, might eat signals , slow react.

resistor dividers bad idea in environment cause again voltages float everywhere not going enough or going on given day

another option use zener diode resistance in front of it, when tried in industrial machine touchy noise

last option might bring up, avr in arduino has internal protection diodes, awesome supressing hit or two, ... lol... once misread zener's 4.7v , 24v, dropping 24 volts + noise , spikes switches, transistors, motors , relays chip

it lasted 2 weeks went ape shit, big ole opto-isolator + 317 setup has worked flawlessly year connected directly mechanical relays switching thousands of times day (with emf protection added)

to honest not big since sent off 10$ pcb's @ itead studio , use smt parts

so theres 2 cents spread out 3 dollars worth of words, 1 of main functions design , make automated equipment in small electronics plant.

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