A typical IR remote uses bursts of 38 kHz interspersed with nothing. This creates what looks like a signal with approximately a 500 Hz. fundamental. The filter will attenuate that frequency by a considerable amount. That is what bandpass filters do. I think you need a deeper understanding of how IR remotes actually work.

I agree with your statement that i need some deeper understanding of IR remote functioning and i admited that earlier.There is no reason to hide it.

 

I would be very thankful if someone could explain this picture a bit.If pass band is 4 kHZ is this mean that detecting freq.would be from 28 to 32 kHZ?

 

No. The 4 kHz region covers the passband, where the filter response is between 0 dB and -3 dB. It is highlighted in green in the diagram above. The stopband is where the filter response is down 40 dB, also highlighted in green in the diagram above. In between the passband and the stopband is the transition band. In this region the response of the filter is between -3 dB and -40 dB. This means that the signals are reduced in amplitude, but are in no way excluded or eliminated. In the analog domain there is no such thing as a "brick-wall" filter with a passband and a stopband, but no transition band.

 

Just for curiousity... How many commands do you want to transmit to the receiver?

 

Just for curiousity... How many commands do you want to transmit to the receiver?

It is simple(at least i thinked so).Two 555 timers are creating oscilations of 30 kHZ.One of the timer is there to create frequency of 30 kHZ with an duty cycle of 60%.Second timer is there to create a burst of impulses.Its frequency is about 700 HZ which output is conected to the reset pin of the first timer.Data is transfered through IR LED and was detected by TSOP 31230.My idea was to make an remote from these two timers which IR impulse would be detected via TSOP,but i found that TSOP also reacts on a standard TV remote so my goal was to prevent that in some way.
It is a DC circuit

 

Will the receiver be shielded from the sun and fluorescent or LED lighting?
The sun can blind simple receivers and the lighting will produce a pulsed output.

 

Will the receiver be shielded from the sun and fluorescent or LED lighting?
The sun can blind simple receivers and the lighting will produce a pulsed output.

I will put receiver in some box or something like that but i tried it already and it works very well in a normal lighted room

 

So, to answer my question myself, you only have one command or pattern which you want to detect? A 700 Hz signal on a 30kHz carrier.

Where am I going with this? If you were to send a series of bursts in a specific pattern, your receiver could only react to that pattern. Let’s say you decide that a one is a 30kHz signal present for 5 ms and a zero is no signal present for 5ms.

I’d create a clock with a 5 ms period. And use a shift register with your command hard coded as input. Let’s use for this example, a signal/command value of 10101010b.

You enable the shift register when you want to communicate with the receiver. And the carry out of the shift register enables your transmitter.

In the other side, receiving a signal enables your clock for enough time to receive the eight bit. Input the receiver output to a shift register and clock in eight bits. Then you can check the register contents with some simple logic to execute whatever you want.

This way, if you have s bits in your command, and b bits are used as a device id and c bits are a command, you can block all other devices and implement as many different signals that you want.

This is a simple approach and I did not address potential issues, but it’s a good start. Normally, I’d suggest a μprocessor solution as we are implementing a custom protocol, but this hardware solution may be all that is necessary.

 

So, to answer my question myself, you only have one command or pattern which you want to detect? A 700 Hz signal on a 30kHz carrier.

Where am I going with this? If you were to send a series of bursts in a specific pattern, your receiver could only react to that pattern. Let’s say you decide that a one is a 30kHz signal present for 5 ms and a zero is no signal present for 5ms.

I’d create a clock with a 5 ms period. And use a shift register with your command hard coded as input. Let’s use for this example, a signal/command value of 10101010b.

You enable the shift register when you want to communicate with the receiver. And the carry out of the shift register enables your transmitter.

In the other side, receiving a signal enables your clock for enough time to receive the eight bit. Input the receiver output to a shift register and clock in eight bits. Then you can check the register contents with some simple logic to execute whatever you want.

This way, if you have s bits in your command, and b bits are used as a device id and c bits are a command, you can block all other devices and implement as many different signals that you want.

This is a simple approach and I did not address potential issues, but it’s a good start. Normally, I’d suggest a μprocessor solution as we are implementing a custom protocol, but this hardware solution may be all that is necessary.

Thank you,but i never used a microcontroler so that is not an option for now.Is there maybe any schematic for your advice?

 

I came across this device which is an IR receiver which doesn't demodulate the IR signal. Its output is a clean modulated carrier so you could put a bandpass after this device to restrict the carrier bandwidth. You would then have to your own demodulation. I don't know whether this will do what you want but it does give you access to the carrier signal.
Vishay TSMP58000

 

T

I came across this device which is an IR receiver which doesn't demodulate the IR signal. Its output is a clean modulated carrier so you could put a bandpass after this device to restrict the carrier bandwidth. You would then have to your own demodulation. I don't know whether this will do what you want but it does give you access to the carrier signal.
Vishay TSMP58000

Thank you very much.I apriciate this.I apologize for my slow respond.
For now i am experimenting with ht12E and ht12D and will see what kind of results i will get.