A Simple OR Gate Circuit For Home Security

Thread Starter

sandipgolani

Joined Jan 17, 2018
8
A simple OR Gate circuit for small home security system, In place of the the switches S2..S5 we can connect various sensors like PIR/Motion sensor, Temp. Sensor, Gas Sensors, Foot Mat Switch etc. The output load is connected with a DIP switch to have buzzer, light or even small MP3 player to automatically play some DOG Barking SOUND.

Home Security_7432_sandipgolani.jpg
 

crutschow

Joined Mar 14, 2008
25,265
Another simple option is to run each switch directly to the transistor base with its own 10kΩ resistor.
Then any closed switch will energize the transistor.
With that you also don't need the resistors to ground at each switch.
 

Thread Starter

sandipgolani

Joined Jan 17, 2018
8
Another simple option is to run each switch directly to the transistor base with its own 10kΩ resistor.
Then any closed switch will energize the transistor.
With that you also don't need the resistors to ground at each switch.
In Electronics options are ocean.
 

AnalogKid

Joined Aug 1, 2013
8,536
Depending on the current ratings of the switches and the load current for whatever the outputs are, you might not need anything - no gates, no transistor, no resistors (except for the output LED).

V+ > load devices > 4 switches in parallel > GND

ak
 

Thread Starter

sandipgolani

Joined Jan 17, 2018
8
Depending on the current ratings of the switches and the load current for whatever the outputs are, you might not need anything - no gates, no transistor, no resistors (except for the output LED).

V+ > load devices > 4 switches in parallel > GND

ak
You are absolutely right ak, but the theme is to add sensors in place of different switches. Otherwise your concept is right adding 4 switches in parallel. Remember my friend OR gate and AND gate development was not required, where we can add switches in series and form AND and connecting switches in parallel we can form OR. I have tried to create a theme now it up to you simplify or magnify ideas.
 

sghioto

Joined Dec 31, 2017
1,334
I don't see any kind of latching circuit for the switches. Normally an alarm would remain active for a period if the switch was returned to open.
SG
 

crutschow

Joined Mar 14, 2008
25,265
Another common configuration is to use NC instead of NO switches.
That way the alarms goes off if a connection is lost or someone cuts the wires.
 

AnalogKid

Joined Aug 1, 2013
8,536
the theme is to add sensors in place of different switches.
If the sensor outputs are relays, then you can connect them as I posted. If they are solid state devices, then simple resistor biasing might not work. Without knowing the technical details of each sensor, combining their outputs cannot be predicted.

ak
 

sghioto

Joined Dec 31, 2017
1,334
Here's my version of an added latch mod. Timer starts when the output of IC1 returns to a low state. Delay time dependent on the values of C1 and R6.
SG
EEE OR Gate Alarm with Latch.png
 

AnalogKid

Joined Aug 1, 2013
8,536
You can add the latch function without the LM393 and most of its parts, by connecting a diode from IC1 pin 8 to pin 1. If you don't want to involve any of the security inputs in the latch function, add IC1D between pins 6 and 10, and connect the diode to the unused input (with a pull down resistor).

ak
 

AnalogKid

Joined Aug 1, 2013
8,536
The circuit in post #13 is not a latch. There is no feedback from the LM393 output to either of its inputs. It is a non-inverting retriggerable monostable whose timeout period starts after the alarm fault has been cleared.

Keep D1, C1, R6. The 4th gate is both the comparator and the diode-OR.

pin8 > pin13
pin8 also > D1-C1-R6 > pin12
pin11 > R5

In fact, the only reason for the 4th gate is as a buffer to drive T1. This reduces the size of C1 because it does not have to provide the T1 base current. It also makes for a more crisp T1 turn off. Add a 2.2 M resistor from pin11 to pin 12 for hysteresis to prevent a noise burst at the T1 collector.

If R6 = 300K, then the delay-off time related to C1 is approx. 1 second per 5 uF. With R6 = 300K, the hysteresis resistor can be reduced to 1 M.

ak
 
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sghioto

Joined Dec 31, 2017
1,334
The circuit in post #13 is not a latch. There is no feedback from the LM393 output to either of its inputs
I didn't say the LM393 was a latch. I said it is a timer. The mod is a latch in the sense it holds the output on when the alarm fault is cleared. You are getting too technical here.;) But I do like your version using the 4th gate, makes good sense, however the LM393 will give a longer delay with same components.
SG
 
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