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logan_dslasher

LOGIC GATES project

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i have spent all day working on the project. at the very last stage of assembling it, i encountered a problem. the inverter input LED doesn't turn ON even if i apply a high to it.. i've traced evferywhere for the fault but found none.. maybe, i'm just too exhausted, so i tried to unwind by playing online games.. i think i'm ok now.. i'll figure out somehow what is wrong..

just a question, one of the LED is not very bright.. it is connected by a foot-long wire. should i shorten it? how about my question about TTL vs CMOS? can they go together in a single circuit?

thanks all for all the help..

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Swap the LEDs. If one side is always dim then the circuit on that side has a problem. Maybe the circuit for the bright side has a problem instead.

TTL and Cmos logic devices are completely different:
1) TTL operates from a 5V supply only. Ordinary Cmos operates with a supply from 3V to 15V or 18V.
2) A TTL input needs a high current to drive it low. An ordinary Cmos output can't supply enough current.
3) A Cmos input needs a fairly high voltage for it to be high. The output voltage of a TTL device doesn't go high enough.                                   

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the problem i encoutered with my inverter was due to the damaged IC.. remember, when i was working on the whistle responder circuit, i used some of the left over parts in making this project.. after i solved the inverter problem, the OR stage malfunctioned.. it's output was always low..

i have solved the problem.. i used the same technique that revealed that my 4081 was defective, since both the 4071 and 4081 have the same pin config, i replaced my 4071 with a 4081. the 4081 worked properly, therefore, the connection was fine. i replaced my 4071 with a new one. it worked fine..

why do ICs gets so easily damaged?

i finished the whole project just in time... i hope my friend will have a good grade.. and i'm pretty confident he would.  8) thanks you guys..

on the other hand, i learned a lot too.. he said the next project they have to pass is an AM radio receiver..

tahnks again for the help..

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