EOL resistor

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.

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

+---+------------+--- +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,