# Explanation needed

Discussion in 'The Projects Forum' started by whycanot, Jul 30, 2011.

1. ### whycanot Thread Starter Member

May 22, 2011
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i have constructed a board accordingly to the schematic shown below.
the circuit consists of 2 parts:
1) IR receiver - for triggering user when there is a thief walked thru ( cut the IR signal from transmitter, it wil sound)
2) heat sensor - for triggering user when there is a fire

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output:
1) when the IR signal is blocked by hand, means when the IR receiver is not receiving IR signal from IR transmiter, LED bight up together wif buzzer sounded for 5 sec.
3) when heated the NTC, both buzzer & LED are ON: IR tat side's LED & buzzer ON for 5sec, heat's LED & buzzer ON as long as it is heated.
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the board is done, but can some one explain the schematic to me?
i have to presentation(explain how it works) to my lecturer this week for this mini project in my diploma

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• ###### ne555n.pdf
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2. ### praondevou AAC Fanatic!

Jul 9, 2011
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Did you tested this? Either I'm missing something or something is inverted in the heat detection circuit. The output of IC1 has to be low for the relay to turn on.
That means under "no-fire" conditions the +input of the opamp has to be above the -input, which is half of the power suppl, i.e. 4.5V.

If the +input is already above 4.5V and the temperature increases then the NTC resistance decreases which means the voltage on the +input increases further, so nothing happens.

Either you swap the 22k with the NTC or use a PTC or change the output logic of IC1.

Then there is a thing I don't understand with the TSOP. Where is it's power supply?
The TSOP receivers work with bursts, I don't know what will be their output signal if you use a continuous carrier signal, what is the frequency of the bursts (not the carrier frequency) you will be using?

Last edited: Jul 30, 2011
3. ### whycanot Thread Starter Member

May 22, 2011
54
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i had constructed according to the circuit~ but it works~

4. ### praondevou AAC Fanatic!

Jul 9, 2011
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Really? Well then YOU need to explain to me why it works... Maybe I'm missing something here...

5. ### whycanot Thread Starter Member

May 22, 2011
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i dunno, that's why im asking over here ><

6. ### praondevou AAC Fanatic!

Jul 9, 2011
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Ok, then let's concentrate on the first part, the fire detector.

You heat up the NTC and above a certain temperature the buzzer begins to sound, is that correct?
If so, then please inform the following voltage levels with buzzer OFF and ON.

Voltage at the + input of the 741
Voltage at the output of the 741
Voltage at the coil of the relay

The 3 voltages for the two states (buzzer on and off) indicating if the buzzer was on or off, please.

7. ### whycanot Thread Starter Member

May 22, 2011
54
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praondevou, thanks a lot for the heat sensor explanation
now i understood
so if now, dun see the upper part of the schematic, we look at the IR receiver
can u explain to me the :
1) when Vo signal out from IR demodulator to the pin 2(trigger) of NE555
2) the pin3(output) of NE555, how the output pin allow the led to light up

8. ### praondevou AAC Fanatic!

Jul 9, 2011
2,939
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I actually find it surprising that the TSOP works. Are you sure you wired this thing as it is in the diagram in your first post? (apart from the heat sensor that was inverted)

Last edited: Aug 2, 2011
9. ### whycanot Thread Starter Member

May 22, 2011
54
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>< i bought it from a shop and i not really sure what its spec ><
but i found this series same wif it in the real pic from internet
the board is really working, i on the transmitter and receiver and put both of them in about 1m range, i put my hand to block the IR signal, and it sounded and brighted up LED for 5s
may u tel how it play around inside the trigger pin and output pin?

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10. ### whycanot Thread Starter Member

May 22, 2011
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this attached pic is the 1st attempt before i integrate it with heat sensor

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11. ### SgtWookie Expert

Jul 17, 2007
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1,761

The schematic in your 1st post cannot possibly work, as the 555 timer GND pin is not connected. Therefore, if your circuit is actually working, then it is different from what is shown in the schematic. You need to correct your schematic to represent how your circuit is actually wired.

The 741 opamp was a poor choice; you should have used a comparator. The LM111/211/311 would have been a good choice.

The image of the schematic you posted in reply #10 gives me a headache.

Both schematics need to be corrected.

You really need to try to follow more conventional schematic practices.

Inputs come from the left, outputs flow towards the right.

More positive voltages on top, more negative voltages towards the bottom.

If you are going to use "power rails", make them straight lines, and connect the components between them. You have them looping all over the place, which makes the schematics really difficult to understand. You have wires crossing each other all over the place, without good reasons for doing so.

What I suggest that you do, is separate the schematics into their two independent functions. You could show them sharing a common power supply.

Last edited: Aug 2, 2011
12. ### whycanot Thread Starter Member

May 22, 2011
54
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Can i explain it like this ? "For the IR Detector, it relies on whether the presence or absence of IR signals. When the IR signals are absence, the pin 2 voltage of NE555 will be pulled low and will not send the triggered pulse. As the output voltage at pin 3 is a NOT OUT, therefore the pin 3 goes high which will first lights up the LED and then forward biasing the base of NPN 9013 transistor, which switches on the relay as well as buzzer."

13. ### SgtWookie Expert

Jul 17, 2007
22,194
1,761
You must create a correct schematic first. Otherwise, you cannot explain how a circuit that cannot work is actually working.

14. ### praondevou AAC Fanatic!

Jul 9, 2011
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I redrew the TSOP part to help everybody to understand why the circuit that cannot work works. (I didn't find the TSOP part in my library)

Have to go out now. Have a look at it later.

Edit: just saw that u are actually not sure what TSOP it is, so we don't know what's it's frequency

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15. ### praondevou AAC Fanatic!

Jul 9, 2011
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A few things are very strange, especially because you say the circuit works.

1. As Wookie said, the GND pin is not connected.
2. The connection of the TSOP to the power supply is not correct. R4 and R5 are in series with the power supply. (82k)
3. Are you sure of the TSOP's pinout? They do not have all the same pinout.
4. What's the frequency of the TSOP?

If the circuit works the way you drew it , it will be very difficult if not impossible to explain why.

In theory it could work like this:
The TSOP is low-active, that means, when it's receiving pulses it will maintain it's output low. Therefore the 555's output is also low because the reset pin disables the 555.
When there are no more pulses the TSOP's output goes HIGH thus enabling the 555. Since the trigger was pulled somewhere in the middle between the 9V power supply it may then trigger the monostable.

However, the current through the 2x41k resistors to Vs of the TSOP would not allow enough current (which is about 1mA @ 5V) to flow.

There is one more ting , the TSOP's are supposed to work with bursts. It's not clear to me, why yours gives you a constant low at the output while it's receiving pulses, even though you don't have bursts, only the carrier.

Please confirm that the circuit you built is exactly like the diagram in your first post. You can also post a picture of the wiring.

16. ### whycanot Thread Starter Member

May 22, 2011
54
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@@ maybe im really lucky enough as the circuit is really working
the attached zip is the video of how my actual board works

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17. ### praondevou AAC Fanatic!

Jul 9, 2011
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Well then I have no explanation. I noticed that the circuit only triggers when you raise the hand, not when you interrupt the beam... Don't know if this means something, though.

Is there really pin 1 of the 555 disconnected?

I'm almost tempted to build this circuit following your schematic.

EDIT: I just saw that your handdrawn schematic is different from your first post schematic. Pin 1 of the 555 IS connected to ground. Also, I'm seeing now that it is indeed completely different. the RESET pin is pulled to +. That's ok so far.

There are too many differences between the two schematics. You really need to provide the correct one.

Are you supplying the TSOP with 9V? If so you are lucky that it still works, according to the datasheet it works with max. 5.5V, right?

Last edited: Aug 2, 2011
18. ### whycanot Thread Starter Member

May 22, 2011
54
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hahaha~ the handdrawn is the most accurate actually as im followed the handdrawn 1. actually i oso dunno which model of TSOP is it >< coz i dun hav its datasheet when bought. maybe it's triggered whenever it receive new pulses after din receive @@ praondevou , can u continue the theory after it trigger the monostable? how it is sounded for 5 seconds? coz i left 27hours more to go to get the explanation >< please , thanks a lot xD

19. ### praondevou AAC Fanatic!

Jul 9, 2011
2,939
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See the attached picture. It's derived from your handdrawn schematic.

"BUS1" on the left side simulates your input coming from the TSOP.

It's HIGH when the TSOP is not receiving and LOW when the TSOP is receiving. (this is true for the TSOP datasheets I've seen)

So normally with the beam uninterrupted the left side of C3 is LOW. When you interrupt the beam, the left side of C3 is charging to Vdd.
When the beam comes back (you raise the hand) the TSOP output goes LOW again, and, since the capacitor itself was discharged, the trigger input of the 555 gets a LOW pulse, triggering the monostable.

Now I understand why it triggers when you raise the hand and not when interrupting the beam.

The time of the monostable is determined by R3 and C2.
Output 3 goes HIGH, LED on, transistor conducts, relay ON, buzzer sounds.

I don't know why the TSOP is still working with 9V, should have been destroyed. But since we don't know what type it is it may be some special high voltage type, even though I don't know if such thing exists.

There should also be a diode in parallel with R1 pointing towards Vdd to avoid raising the voltage on the trigger input higher than Vdd each time you interrupt the beam.

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20. ### whycanot Thread Starter Member

May 22, 2011
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the tsop, Vs is the output or Vo is the output that changes when detect IR ?