semiconductor

Some questions related to LM567 (tone decoder)

I'm working on a project. My duty is that: I have to detect a signal radiated from an IR LEDs. I use the SFH506 to demodulate the modulated signal (carrier frequency is 40kHz). I know the information frequency, it is: 40 Hz. I have to detect this frequency.
My tutor said that, I should use the IC LM567 to detect this frequency. When this frequency signal is applied to PIN 3, the output PIN 8 will be at LOW (other cases, PIN 8 always be HIGH).

When I carried out the experiment. I've got some problems.

- central frequency of LM567 is defied by R which is connected between PIN 6 and GND and C which is connected between PIN 6 and PIN 5. I chose R and C so that, the central frequency is 40 Hz (fo=1.1RC). Besides, I put between PIN 2 and GND a capacitor

- I decided to try this case: links PIN 5 (pulses with duty cycle is 50% and f = fo) to PIN 3 (input). I hope that PIN 8 will change its state (from HIGH to LOW). But it's not the case. I use oscilloscope to display pulse shape at PIN 8 when I apply the link between PIN 5 and PIN 3, first, the pulse shape on oscilloscope appears, then the duty cycle of this pulse decreases so after about 10 seconds, it's GND (Voltage at PIN 8 equals to 0). When I remove this links, the LOW state of PIN 8 maintains and after 10 minutes observing, this state does not change.

- first, I don't know why? I think, when there's no signal at the input PIN, the output PIN must be HIGH (not LOW forever).
- second, does LM567 operate as I said before? that is: when there's a signal with frequence within its bandpass (fo +/- num), output PIN will be LOW and be HIGH again vice versa (opposite case).
- Last, Can some one recommend me some other solutions to my problem (detect a fixed frequency signal)?

My due date is coming soon and I really need your helps
thank in advance!
Binh, From Vietnam.

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Sebi

Your circuit equal with this?

Attached Images

567.GIF (4.6 KB, 499 views)

semiconductor

The PIN 3 is connected to PIN 5 between Resistor 2.5K and capacitor 0.004 mfd.

I'll post my schematics later if possible!

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ariakovo

My i ask how long is the transmition range that you achive between the transmiter and the receiver because i trying to do something like yours and i can't achive a long range.Sorry for your time

Nigel Goodwin

You should easily exceed 10m, it's a really trivial task - but you MUST send suitable data, you can't send just a carrier, or the AGC turns the gain right down.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ariakovo

If i have a simple frequency it isn't possible to achive this distance?In the receiver i will put a phototransistor a transistor as an applifier and the lm567 to detect this frequency if exists high otherwise low.I haven't an IC(ir module like TSOP22.. Vishay).I can't put data in there.Any idea?

Nigel Goodwin

You can make your own IR receiver with a photodiode and amplifiers - but it's not a trivial task, and an IC receiver is so much easier.

The IR receiver IC's are in almost everything that has remote control, take one out of an old TV or VCR.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ariakovo

he IR receiver IC's are in almost everything that has remote control, take one

I understand but i have use the ic's and i can't achive the distance because i have to send data.I can't send data.I don't have the space and it is expencive.So i have to use a phototransistor and take the frequency on my own with the way i explain before.I want to make sensors that detects objects.Can i achive this distance with the way i explain?Thanks

Nigel Goodwin

I don't see as a simple 8 pin PIC is 'expensive'?, and that would do everything you need at the transmitter, and one at the receiver as well.

If you want to use plain frequency modulation then go the photodiode and amplifers route, but it's FAR more difficult and much more expensive.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ariakovo

The cost for the emitter is only a clock that is 0.3$ and the ired.For the receiver is the lm567 = 0.3$ and a transistor after the phototransistor that is 0.1$.If i use microcontroller is more expensive?Also i need space i don't have much space.But i believe that it is achivable.The only thing to do is to work the current that flows the phototranistor.Thanks

Nigel Goodwin

That's why you're getting no range at all, you're not driving the IR LED with any current, and you don't have any amplification on the receiver. To make it work at the distances you want you need to make it a LOT more complicated and expensive, MUCH more than simple PIC's (under 1$) and an IR receiver IC.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ariakovo

Ok i will check both sides.Can you propose me a PIC that i can do this?If i applify the receiver and then put the output of the applifier in the lm567 will i have the same result in long distances?

Nigel Goodwin

Any PIC would do it easily - but there's not much point using a PIC on the transmit side if you don't use one on the receive side, along with an IR receiver IC. If you're going to the expense and trouble of building a high gain amplifer for the receiver, with all it's instability problems, you may as well use a 555 or something for a blank carrier on the transmitter.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ariakovo

I see.I will use both ways.First i will use the hard way to make the receiver on my own.And after i will use a PIC.The reason is that i don't know things about microcontrollers yet.I have oreder the components for the hard way.So i will study PICs and then we will see.Thanks any way.I will use phototransistor because it is more sensitive than photodiode and has 1000 or 1500 gain.So i can use it so easily.I have to make mechanical filter for the daylight plasitc glass to let pass only the ir length of light(880nm - 960nm).C U