Hi, what I am looking for is the circuit from the switch to the microprocessor. As mentioned a protective loop
Thks Rob
EOL resistor
Mar 17, 2009
3 Replies
Hi I am building a alarm circuit. I want to use a EOL resistor to provent bypassing the alarm zone by short circuit. I need the circuit between the switch and the microprocessor. Have seen this on professional systems normally use a op amplifier or two.
Thks Rob
You terminate at sensor with known value resistor.
At alarm box, use window detector (Google it), such that open-circuit OR short trips alarm.
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+---+------------+--- +V | | | | 10K 100K | | |\\ | 1K +------|+\\ | | | | >--+ 2 comparitors | | .---|-/ | with O/C output | | | |/ | eg. 2/4 LM339 .---o--o---+---|--+ | | | | |\\ | | 2.2K `---|+\\ | | end of | | >--+--- to microcontroller 1K loop +------|-/ | resistor | |/ | 10K | | `--------------+--------------------- 0V if you have a microcontroller with DAC inputs you can use them directly instead of the above circuit,
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