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Infra Red Alarm System HELP.......

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Jordan_Zillen

New Member
Hey there Guys,

A while ago i managed to get my hands on a couple of old electronics magazines, "Electronics Africa", in it i found an on going article on how to build an infra red alarm system.(Picture attached)

Although it may be an old design, I have decided to try build this project, but have come into a few problems, and was wondering if any one could assist me? When the project is switched on, the relay is automatically triggered, therefore switching my siren on permanently(Broken beam).

I managed to get hold of most of the components listed, except for the BPW14(Photo-transistor) used in the receiver unit. My electronic outlets dont stock this item any more as it is an old component. With some digging, ive come across the newer components such as the TSOP1736, which reads a 36kHz signal... where as my circuit runs on a 1kHz signal. Now i've tried out a transmitter that sends a 36kHz signal, but this does not work? Would i need to re-design my control board to allow for the higher signal?

I've also tried using the PT202C(Photo LED), using the 1kHz signal. When using my multi-meter, i can see the transmitter communicating well with the PT202C, but still have no success in the actual circuit working. Ive checked and RE-checked all my wiring, and everything appears correct.

I dont get much of a signal out of my receiver, after passing through C3(470pF), which could be part of my problem? But also D2(IN4148) on the control board is suppose to rectify a negative voltage from C11(100nF)... which it does not do? Ive tested the diode, and it IS working.

How do i get T3 to switch on, in turn switching T4 off.... meaning an unbroken beam?
I have also made the necessary adjustments with my power supplies, to get the recommended voltages, and currents...

Please if any one can help me id be eternally grateful!!!!

thanks very much.
 

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audioguru

Well-Known Member
Most Helpful Member
The TSOP1736 IR receiver iC does not read a 36kHz signal. It reduces its gain when it receives continuous 36kHz pulses. It has high gain when it receives 36kHz bursts of pulses.
It is easy to make a circuit modulate the 36kHz pulses into bursts that have the number of pulses and the length of pause as described in the datasheet.

But the output of the TSOP is data, not a continuous DC level that is needed to make a "broken beam" detector.
 

dougy83

Well-Known Member
If you did want to use the tsop1736, you can modulate (e.g. turn it on & off) the 36khz going to LEDs. Also, the tsop1736 has all the smarts in it to do the filtering & detection of the IR signal, so your receiver cct is greatly simplified.

I've drawn up a quick sketch of how I might wire it. The top part is the transmitter, which should produce a 36kHz carrier (you may need to tune this), switched on/off at 500Hz. The bottom part is the receiver; the tsop.. outputs a stream of low pulses when the beam is unbroken which keeps resetting the 555 monostable, which in turn outputs a constant high. If the beam is broken for long enough for C3 to charge through R5, it triggers the next 555 which outputs a high level while the beam is broken and for a second after the beam is returned.
 

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Boncuk

New Member
Hi dougy,

I suggest to recalculate the timing values for R and C of your circuit.

The given values are correct for approximately half the frequency.

For timer X1 the values are C1=100n, R1=14.488KΩ

May be you observed only 1/2 cycle on the scope? :)

Boncuk
 

dougy83

Well-Known Member
Boncuk, quite right. The frequencies will be half the stated frequencies. So just divide the timing resistor values by about 2 for the transmitter cct.
 

Jordan_Zillen

New Member
hi, thanks for your suggestions guys, i will definately give it a try.

dougy, do you think the circuit modifications you supplied will work with my current set up of control panel?
 

dougy83

Well-Known Member
dougy, do you think the circuit modifications you supplied will work with my current set up of control panel?

The top circuit I supplied replaces the transmitter and the lower circuit replaces receiver & control boards. Feed the output of the lower right 555 into a 5V relay and the relay will operate when the beam is broken.

Note the receiver is now run from 5V due to the power requirements of the tsop1736. The transmitter can be run from whatever it was run from before.
 
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Boncuk

New Member
Boncuk, quite right. The frequencies will be half the stated frequencies. So just divide the timing resistor values by about 2 for the transmitter cct.

So you just calculate what frequency you will end up with for X3.
 

dougy83

Well-Known Member
I'm not sure if that was a question.. But if R2 is 1k8, the carrier is ~35.5kHz. If R1 is 12K, X1 output is ~600Hz
 
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