go_away

Author Topic: Basic IR alarm system  (Read 1811 times)

0 Members and 1 Guest are viewing this topic.

Offline BANETopic starter

  • Supreme Robot
  • *****
  • Posts: 639
  • Helpful? 4
  • E=roboticsC^2
Basic IR alarm system
« on: November 27, 2007, 04:51:24 PM »
What Im trying to make is an alarm that will activate when input from an IR detector is cut off.  Similar to the types of motion detectors in banks or where every there used.   From the schematics below, the IR emitter LED and power indicator LED will always emit regardless of transistor.   What I want is as long as the IR receiver detects IR that the Piezo Speaker will be deactivated and as soon as the IR is disrupted the Piezo speaker sounds alternating between two frequencies farley fast.     

see attachment for schematics

The two main problems that Im having is finding a transistor that will cut of the power supple when current is flowing and turn it on when not, and how to activate the piezo speaker using the 5v current and the components that will make it alternate between two speakers. 
   Are there any problems in the schematics? 
   Does a transistor that will perform my desired function exist?   
   What components will make the Piezo speaker activate and alternate between the two frequencies and can I buy them from Radio Shack or Digikey?

Bane
« Last Edit: November 27, 2007, 04:53:31 PM by BANE »

Offline bukowski

  • Robot Overlord
  • ****
  • Posts: 219
  • Helpful? 0
Re: Basic IR alarm system
« Reply #1 on: November 27, 2007, 05:58:34 PM »
I think this might work -

Excuse the horrible art work!!

R1- 220 Ohms
R2- 10 Ohms
R3- 220 Ohms
C1- .1 uF
Q1- NPN 3904
Q2- PNP 3906

Like I said, im not positive this will work, (Im no EE) but it makes sense to me. If anyone sees anything wrong, let me know.
-Buk

Offline bukowski

  • Robot Overlord
  • ****
  • Posts: 219
  • Helpful? 0
Re: Basic IR alarm system
« Reply #2 on: November 27, 2007, 08:21:01 PM »

That's a little better.
I finally left work!
-buk

Offline BANETopic starter

  • Supreme Robot
  • *****
  • Posts: 639
  • Helpful? 4
  • E=roboticsC^2
Re: Basic IR alarm system
« Reply #3 on: November 28, 2007, 05:03:05 PM »

-buk


Hey Buk, thanks for the reply and I think I'm going to try to build it this week end.  I've got a question about the speaker.  Is it a Peizo speaker?  (sorry I'm new at reading schematics)  And Can it alternate between two different frequencies depending on resistor type and the timing? (if thats how they work)  I'm also new at working with transistors and wondering about that switch thing with the circle around it.

Bane

Offline bukowski

  • Robot Overlord
  • ****
  • Posts: 219
  • Helpful? 0
Re: Basic IR alarm system
« Reply #4 on: November 29, 2007, 02:15:40 PM »
No, that's not a peizo speaker, just a normal low fidelity paper cone speaker. I have no experience working with piezo speakers, but from what I just read, they have a tendancy to have high capacitive reactance which can be bad in amplifier circuits.

Like I said, there is no guarantee that this circuit will work, It's just a similar design to a circuit I experimented with, with a photoresistor instead of the IR detector.

Q3 is meant to represent the IR detector. D1 is the IR LED. Using a cheapy cone speaker from radioshack this circuit should give you an alternating tone, maybe not a pure two tone, but close.

I'll tell you what, let me pick up the LED and phototransistor, and I'll breadboard it this weekend and ill let you know if it works.
 

 


Get Your Ad Here