burglar alarm system

[meowth08]

Design a burglar alarm that will sound a 5kHz, 5 watt sound. An alarm switch is built into the left front fender of the car. It is normally an open switch. When the key is turned to "armed position", the switch is closed. A motion switch is mounted into the automobile such that when any motion occurs, a momentary contact is made. When any disturbance to automobile occurs, the output signal momentarily drops to zer0(ground). The burglar alarm should sound the 5kHz signal only if the fender was previously armed. The alarm should sound for two(2) minutes and then shuts off.

Additional requirement: Use NE555 for the design and other components needed to accomplish the design.

I hope you can help me with a diagram.

Any help from you guys will be very much appreciated. Thank you.

 

[ericgibbs]

Design a burglar alarm that will sound a 5kHz, 5 watt sound. An alarm switch is built into the left front fender of the car. It is normally an open switch. When the key is turned to "armed position", the switch is closed. A motion switch is mounted into the automobile such that when any motion occurs, a momentary contact is made. When any disturbance to automobile occurs, the output signal momentarily drops to zer0(ground). The burglar alarm should sound the 5kHz signal only if the fender was previously armed. The alarm should sound for two(2) minutes and then shuts off.

Additional requirement: Use NE555 for the design and other components needed to accomplish the design.

I hope you can help me with a diagram.

Any help from you guys will be very much appreciated. Thank you.

hi,
Do you have a rough idea how you could connect say two 555 timers in order to meet the design requirement.?

For example, one 555 set as an Astable for 5Khz and the other a Monostable for 120 second period.??

 

[meowth08]

The time a monostable vibrator is on (logic 1) would be 1.1RC.

To output the 5 kHz, I may use this equation. f = 1.44/(C1(R1+2R2))

 

[meowth08]

I still dont know how the connection between the astable multivibrator and monostable vibrator would look like.

 

[Boncuk]

I still dont know how the connection between the astable multivibrator and monostable vibrator would look like.

Check out what the "Reset"-pin can do for you!

BTW, using the formula T=1.1RC for the monostable time delay resistance of 1.1MΩ and capacitance of 100µF are correct values to get near to 120 seconds.

Putting those values into the formula the result is 121 seconds, and not 110 seconds as you stated in the chat yesterday. My original calculation resulted in 120.8 seconds.

I hate if the egg gets smarter than the hen.

Boncuk

 

[meowth08]

https://www.facebook.com/photo.php?fbid=331504210198176&set=a.331504043531526.107219.100000157991071&type=3&theater

 

[meowth08]

https://www.facebook.com/photo.php?fbid=331504093531521&set=a.331504043531526.107219.100000157991071&type=3&theater

https://www.facebook.com/photo.php?...3531526.107219.100000157991071&type=3&theater

 

[ericgibbs]

https://www.facebook.com/photo.php?...3531526.107219.100000157991071&type=3&theater

hi,
Copied your image from Facebook, here it is.

 

[ericgibbs]

hi,
You dont need the amplifier between the tilt switch and the Monostable
Do you want me to show you how to connect the tilt switch?

Pin 1 of the 'astable' needs connecting to 0V

Pin 3 of the monostable should go to pin 4 of the astable. Pin 8 should be connected to +12V, NOT pin to pin 4.

I cannot read the values on your formula's , too blurred to read.

 

[ericgibbs]

hi,
Look at this for the 555 and tilt switch and arming switch.

Use your values in the ? marked components

 

[meowth08]

@ ericgibbs, the requirement of the design problem states that the alarm will only sound if the key is in armed position( the arm switch is closed) then a disturbance occurs( meaning the tilt switch is triggered). As I understand this diagram, the alarm will still sound even when the key is not in armed position (arm switch not closed) since there is no interconnection between the tilt switch and the arm switch.

 

[meowth08]

@ericgibbs,

the design problem requires that the alarm will only sound if the key is in armed position (the arm switch closes) and then a disturbance is made which will trigger the motion switch (tilt switch). On your diagram, I think that the alarm still sounds even when the arm switch is not closed. There is no interconnection between the arm switch and tilt switch.

 

[ericgibbs]

@ericgibbs,

the design problem requires that the alarm will only sound if the key is in armed position (the arm switch closes) and then a disturbance is made which will trigger the motion switch (tilt switch). On your diagram, I think that the alarm still sounds even when the arm switch is not closed. There is no interconnection between the arm switch and tilt switch.

I would suggest you relook at the circuit, the ARM switch controls the supply to the alarm system, so how could the alarm sound if the ARM switch is OFF.???

There doesn't need to be a connection between the ARM and Tilt switches.!

 

[meowth08]

I was inspecting the schematic you gave. I think the alarm will sound automatically after the power switch is closed since there is a voltage source from R5 which will directly go to pin 2.

 

[meowth08]

The pulse begins when the 555 timer receives a signal at the trigger input that falls below a third of the voltage supply.

It will not sound automatically since the trigger (pin2) of the monostable requires an input lower than one-third of the supply for it to operate. The only time that the monostable will be triggered is when the tilt switch is also triggered. The voltage source from R1 will be bypassed. But what happens to the voltage source above R5? Would bypassing the voltage above R1 provide the necessary voltage to the trigger(pin 2)?

I also looked at the internal circuitry of the 555 timer and I'm sad to say that I cant fully understand it.

Sir, I admit I'm not a quick learner but I strongly believe that with my dedication to learn with the joint efforts from this site will help me accomplish things with full understanding.

 

[meowth08]

The last one you showed me Sir is the datasheet from Philip Semiconductors. I have read that already but I also failed to digest how AC coupling would provide the necessary 1/3 of the supply voltage to trigger the monostable. Is it the charging of the capacitor?

 

[ericgibbs]

The last one you showed me Sir is the datasheet from Philip Semiconductors. I have read that already but I also failed to digest how AC coupling would provide the necessary 1/3 of the supply voltage to trigger the monostable. Is it the charging of the capacitor?

hi,
I did post on Chat for you yesterday, these two images.

I have used a 100nF cap in place of the actual 10nF in order to show more clearly the voltages and currents in/out of the Trigger capacitor.

You should be able to work it out.

Hint: Assume both ends of the 10n are at +12V, then connect the input end of the 'uncharged' cap to 0V, what will the voltage at the 10K end of the 10n cap swing too.?????

 

[meowth08]

Since it is grounded the voltage of the capacitor would drop to zero too.

 

[ericgibbs]

Since it is grounded the voltage of the capacitor would drop to zero too.

hi,
As the capacitor has the same voltage at both ends the net charge on the 10nF cap is zero

If the 1K end of the 10nF cap is connected to 0V, there is now 12V across the capacitor, so the cap will start to charge via the 10K.

At the instant the 1K end is connected to 0V, ALL the 12V is dropped across the 10K due to the current flowing in the 10K to charge the 10nF cap, so pin 2 is momentarily connected to 0V.
As the 10nF cap charges, the voltage on the cap increases, so does the voltage on pin2.

OK.?