IR Module with 555 Question.

[Suraj143]

Hi guys I have a problem.

I’m using TSOP1738 IR module Receiver & a 555 IR transmitter.

If I make a 555 astable circuit for a 38Khz frequency on a 50% duty cycle & focus onto IR module does the IR module make low or does it toggling at a rate of 38Khz?

Because I have read somewhere IR module need some minimum burst length to produce its output.

Thanks

 

[Number17]

You need to modulate the 38khz signal, or else the TSOP will do nothing. The Tsop is inverted so it is in an active high output if nothing is sent to it.

 

[Suraj143]

So you telling if I focus IR transmitting LED's to the module the TSOP module output will do not anything?

 

[Number17]

Yes, you need to mix the 38khz signal with another signal. It can be done with a AND gate. Then the TSOP's output will be the second signal but inverted.

 

[Suraj143]

Hi thanks.

What I want to do is I have NE 555 38Khz transmitter.Its focusing on to TSOP module at 3-4M length.

When somebody crosses it it must turn on a relay thats it.

This is what I'm going to make.Any idea how to do.

 

[Number17]

I am going somewhere now, but when I get back I'll help you.

 

[Suraj143]

I saw a project it has only a 555 transmitter & it doesn't have any AND gates just a astable configuration.

Its focusing to a IR module circuit & it will turn on a relay nicely.It had a 14 pin IC to detect IR beams its not a micro controller.

 

[HarveyH42]

If you put an LED on the output of the module, it will be light up normally. When you point your 38kHz IR signal at the receiver module, the LED will go dark. So yeah, you are all set. Replace the LED, with a driver (transistor) suitable for your relay. One other note, the receiver modules usually have an AGC (automatic-gain-control), so you might get shorter range. More circuitry would only send burst of the 38kHz signal, and after the receiver you would check to see if you are missing pulses. For your range, shouldn't matter though. I don't know if the receiver can drive a relay directly, don't think it will, unless it's very low power. A GP transistor, resistor, and diode is all that's needed to drive.

 

[Boncuk]

Hi,

you should use two astables, one to create the "carrier" wave of e.g. 38KHz and transmit bursts of the 38KHz signal of 600µs duration with a break of 600µs.

The transmitted pulse pattern should look like this:

Boncuk

 

[Suraj143]

If you put an LED on the output of the module, it will be light up normally. When you point your 38kHz IR signal at the receiver module, the LED will go dark. So yeah, you are all set. Replace the LED, with a driver (transistor) suitable for your relay. One other note, the receiver modules usually have an AGC (automatic-gain-control), so you might get shorter range. More circuitry would only send burst of the 38kHz signal, and after the receiver you would check to see if you are missing pulses. For your range, shouldn't matter though. I don't know if the receiver can drive a relay directly, don't think it will, unless it's very low power. A GP transistor, resistor, and diode is all that's needed to drive.

A very good reply.Now I understood.So in receiver side i needs only few components & no need special IC's.

Regarding burst

I'm sending continuous 38KHz frequency on 50% duty cycle.The reason for IR module goes low when I point the IR transmitter because the module sees this continuous pulses as a burst.

To make it long range I'd send pulses in intervals ex- 500uS pulses,500uS off pulses.continuous....

Tell me am I right?

 

[Suraj143]

Hi Boncuk thanks for your reply.Using two astable makes IR pulses longer?

So still the receiver side has only few components.

 

[birdman0_o]

Hopefully somebody will correct me if I'm wrong, but can't you turn down the duty cycle to even 10% to save power. Isn't it only the frequency that matters?

 

[Boncuk]

Hi Boncuk thanks for your reply.Using two astable makes IR pulses longer?

So still the receiver side has only few components.

Nope. IR pulses won't be longer, but interrupted remaining at the frequency your receiver is tuned for.

Receiver chips like the TSOP series (Vishay) reduce sensitivity by AGC if they receive a constant signal.

Check out any TSOP (most common are TSOP248X and TSOP 17XX series) datasheet. Recommended pulse pattern is the same for all kinds of receivers.

Using a dual timer IC (NE556) you might create the control signal by the first half of the chip resetting the second half every 600µs (meaning no transmission for that time) resulting in pulse bursts of the desired duration.

The effect is similar to pushing a bell button at intervals.

The receiver side won't have to be changed. Just hook up the receiver like you would do using a continuous signal.

Boncuk

 

[Suraj143]

Ok Boncuk I planned to use your technique.

But in your technique doesn’t the relay toggle?
Because its sending 600uS on time & 600uS off time bursts?

 

[Number17]

No the relay will not toggle. A relay is big and bulky and cannot possibly toggle at 833Hz