[SOLVED] Burglar Alarm Circuit

[Audioguru]

I already told you in post #25 that a TSOP1738 IR receiver IC (it is obsolete and is not made anymore) WILL NOT WORK unless the IR transmitter modulates the 38kHz in bursts.

 

[DasPreetam]

So, any substitute IC that works like TSOP1738 ??

 

[Audioguru]

The TSOPxxxx was used in TV and home entertainment remote controls. Remote controls are still made so ICs for them must be available somewhere.

 

[DasPreetam]

Sorry for posting after so many days, was busy with some work...

The Problem is, I understand the TSOPxx38 or other 38KHz receivers will not work unless it receives the signals in bursts. But how can I design the transmitter to give out signal in Bursts. I mean, it's an astable multivibrator right ?

 

[Audioguru]

The 38kHz oscillator is gated by a low frequency oscillator. Then the 38kHz IR is in bursts.

 

[DasPreetam]

I didn't get you Audioguru... can you explain it a little bit ?

 

[Audioguru]

Bursts are a period of 38kHz output then a period of no signal, over and over.
The 555 that produces 38kHz can be gated (turned on and turned off) with a voltage on its reset pin. A second 555 running at a low frequency can gate the 38kHz oscillator by driving its Reset pin.

 

[DasPreetam]

So two astable multivibrators... MVA running at suppose 100 Hz and MVB running at 38 KHz with pin 3 of MVA connected to pin 4 of MVB (here MVA and MVB are two multivibrators). Will that work ?

How to know the interval between bursts, I mean will 100 Hz work or should I try something higher/lower ?

 

[Audioguru]

The datasheet for the TSOP1738 shows the spec's for the bursts and pauses between bursts.
One cycle of 38kHz is 26.3us long. A burst must be >10 to 70 cycles so 30 cycles are about 0.8ms long. The pause time between bursts must be at least 14 cycles so make it a little less than 0.8ms. Then the frequency of the bursts is about 780Hz.

Note that the waveform from a simple 555 oscillator is not symmetrical. Its output high time is longer than its output low time. The 38kHz oscillator makes a burst when its reset pin is high.

 

[DasPreetam]

Found a solution to the problem ! The datasheet of TSOP4038 by Vishay Semiconductors states that it accepts continuous IR pulses of 38KHz frequency. So guess the transmitter problem is over now. What do you say ?

 

[Audioguru]

The new TSOP4038 will malfunction when exposed IR from sunlight, incandescent light and compact fluorescent light.
The old IR receiver ICs suppress interference from these sources of IR.

The remote for my TV works fine when the room has sunlight, incandescent light and compact fluorescent light. I can point the remote away from the TV (actually I can point it behind me) and it works fine. It probably will not work with the new receiver IC unless there is total darkness.

 

[DasPreetam]

I am quoting from the datasheet

The TSOP4038 is a compact IR receiver for sensor
applications. It has a high gain for IR signals at 38 kHz. The
detection level does not change when ambient light or
strong IR signals are applied. It can receive continuous
38 kHz signals or 38 kHz bursts.

 

[Audioguru]

When they say "the detection level does not change when ambient light or strong IR signals are applied" then I think they are saying it gets overloaded by strong IR which causes it to malfunction.
That is why the original TSOP IR receivers worked with bursts of 38khz because their AGC reduced the gain when continuous IR was received.

 

[DasPreetam]

Okay here's another design of the circuit. The bulbs x1 and x2 will be replaced by buzzers. I'm thinking of replacing bulb x1 with a 12V car horn (something that would make a very loud sound). The bulb x2 will be replaced by a less louder 6V buzzer (so that it doesn't drain out the battery much). The 6V buzzer will only sound when the mains supply are OFF.

My question is, is the 2N3055 transistor fit for the job ? Or should I use something other ? My requirements are low cost, and compact size. I don't know much about the power ratings so please help me on this topic. Also, is the 2n2222 fit for the 6V buzzer ?

 

[Audioguru]

There are little car horns that make a squeak and there are big car horns that sound like a huge truck. Since you did not say how much current yours uses then your circuit might not work since the 2N3055 transistor has very low base current and a diode is missing across the inductive horn.
The same goes for the relay. How much current does it use? Also add the diode.

 

[DasPreetam]

No I'm talking about the horns of small cars/motorcycles... Not that of a truck... That'll give the burglar a heart attack LOL...

 

[Audioguru]

No I'm talking about the horns of small cars/motorcycles... Not that of a truck... That'll give the burglar a heart attack LOL...

I have never been to your country so I do not know small cars and there are few motorcycles. I have never seen a 6V horn.
The horn is made by a manufacturer who has a datasheet for it. Get the datasheet and tell us its current.

 

[DasPreetam]

Okay guess its time to hit the automobile market...

 

[DasPreetam]

By the way, leaving the horn part, do the other things look okay ?

 

[Audioguru]

By the way, leaving the horn part, do the other things look okay ?

We don't know because you did not update your schematic that has light bulbs on it.
The circuit needs a supply bypass capacitor as shown and discussed on the datasheet for a 555 timer.
we do not know if your buzzer is inductive and if it is then it needs a diode across it.

I think you must learn about the TSOP IR receiver:
The base of your transistor Q1 will hold its output at a low voltage which is wrong as is said on its datasheet.
The TSOP and transistor are turned on by an IR beam. When the burglar blocks the beam then the transistor turns off then the trigger pin 2 of the 555 goes HIGH.

I think you must learn about the 555. It is triggered when its pin 2 goes LOW (when the burglar is gone). Then the buzzers sound and the timer begins. But it will never timeout because pin 2 is held low by transistor Q1.

The 555 will timeout if you capacitor-couple the LOW signal to its pin 2 from transistor Q1.