Simple IR Transmitter and Receiver

[TheAppleMac]

Hi, I want to make an RC car (don't we all ) and I have figured out that I need an astable with an output of IR LED. The question is, how do I set up an IR receiver? I have heard about and seen components which are IR receivers, but they only respond to 38kHz or so. I want a receiver circuit, just to switch a motor on/off and it can be modified to "accept" certain frequencies, but not interference from other transmitters, so that the frequencies can be differentiated. I.e. a transmitter of 5kHz and matching receiver, and another 30kHz transmitter with matching receiver, without interference from one another. Much appreciated.

BTW, I am a complete newbie, so the simpler the better. Thanks for your time.

 

[audioguru]

The amplifier of a car controlled by a transmitter at 5kHz must have a sharp bandpass filter at 5kHz that rejects other frequencies. Then a second car might be controlled with 10kHz if the filters are sharp enough. If the transmitter produces a 5kHz square-wave then a 15kHz and 25kHz receiver will pick it up due to the odd harmonics in a square-wave.

 

[TheAppleMac]

bandpass filter at 5kHz that rejects other frequencies.

I have actually got that already (although thank you for about the advice about the square-wave harmonics.)

I would like to know how to receive that frequency and power something with it. I know that you need a photodiode (I am also told that you need to put it in a potential divider, I do not know if this is correct), but how do I add the filter to the photodiode? Or am I missing something altogether?

 

[audioguru]

You can use the photo-diode as a tiny solar cell or bias it in reverse and let it leak current when it receives IR. Then you amplify the pulses it produces.
Then you filter the pulses with a bandpass filter. Then you rectify the signal and it controls the motor.

 

[TheAppleMac]

I think I get it. Just to recap:
The 555 astable produces a frequency, which is transmitted by an IR LED. The photodiode "sees" this and it produces the same frequency as the astable, as it goes high every time the astable is high...etc. These pulses are what causes frequency and is filtered by the bandpass filter, to stop any other frequencies from interfering. This then powers the motor.

Does this make sense? Or am I missing missing something (again)?

Thank you for your quick response.

 

[TheAppleMac]

Just realised a problem with this:

If I was to build the circuit described in my previous post, then wouldn't the photodiode continuously give a high output, due to background lighting?

And if I was to use some sort of comparitor, would the IR LED be bright enough to make much of a difference?

Confused.....

 

[audioguru]

I think I get it. Just to recap:
The 555 astable produces a frequency, which is transmitted by an IR LED. The photodiode "sees" this and it produces the same frequency as the astable, as it goes high every time the astable is high...etc. These pulses are what causes frequency and is filtered by the bandpass filter, to stop any other frequencies from interfering.

Yes.

This then powers the motor.

No.
The output of the photodiode is low voltage, low current, high frequency AC. It must be amplified then rectified to DC which activates a switching transistor or Mosfet that powers the motor.

If I was to build the circuit described in my previous post, then wouldn't the photodiode continuously give a high output, due to background lighting?

You use an IR photodiode that responds to IR and ignors most visible light.

And if I was to use some sort of comparitor, would the IR LED be bright enough to make much of a difference?

Use a comparator where? With a bright IR LED shining on an IR photodiode at a few meters distance then the output level of the photodiode is so small that it needs amplification to reliably activate a comparator.

 

[TheAppleMac]

Ok, thank you. But where can I find an IR photodiode? I search on google, and it comes with either infra red LEDs or just regular photodiodes?

 

[audioguru]

An IR photodiode or photo-transistor is in a black case that blocks visible light but passes IR.
I got this photo from Google Images:

 

[TheAppleMac]

Oh, actually I just googled IR diode instead of IR photodiode. Doh!

I think that answers all my questions, thank you sooooo much, you have really saved me a lot of time and trouble, thank you!

 

[TheAppleMac]

Opto Coupler Help

Hi guys, I started a forum a couple of days back about a simple IR transmitter and receiver. If I wanted to put in a component which responds immediately from an IR signal, which would I use? From what I gathered here, the answer is an IR phototransistor, however I only know how to set up a photodiode. How do I set up a phototransistor into my circuit? Thanks for your help.

 

[audioguru]

A photo-transistor is slow. It responds to slowly turning on and off the IR.
A photo-diode is fast or very fast. It responds to the IR varied at a low or high frequency.

When a photo-diode has its output amplified then it has the same or more sensitivity as a photo-transistor but it is fast.

Use an IR receiver IC. It has a photo-diode, amplifier and bandpass filter. TVs and DVD players use them.

 

[TheAppleMac]

Thank you

 

[TheAppleMac]

Transistor Amplifiers

Hi, I would like to know how to set up a simple transistor amplifier circuit. I have searched google, however it gave me mixed results, and I would like to know how effective the amplifier is from you. Preferably, it has to be simple, but also it has to amplify well, considering the input is from the current leakage of an IR diode, and it has to power a motor.
Thanks.

 

[alec_t]

How rapidly do you expect the IR current to change? Is the current modulated (e.g. is the IR source pulsed at 38kHz)? What are the voltage and current requirements of the motor?

 

[TheAppleMac]

Ok, I have not actually built the circuit. But I have designed it to operate with one frequency operating a motor at 5kHz and another at 17kHz. I have designed all the necessary filters. This is all completely theoretical (for now). The motors are going to be used to power a RC car, so they will frequently switch on/off. What do you recommend?

 

[audioguru]

Why did you start another thread about your simple RC car?
You must study IR detector circuits, amplifier circuits, rectifier circuits and power driver circuits.

I think 17kHz is so close to the 3rd harmonic (15kHz) of 5kHz that both receivers will activate at the same time.

 

[Ziddik]

a TV remote controller produces IR signals in 38Khz, so u dnt need to build another transmitter for 38khz If u want use the tv remote controller

 

[TheAppleMac]

I have 3 frequencies at 19kHz, 27kHz and 43kHz.
Just trying to draw the circuit diagram to build, however something that struck me is that the IR LED will try to flash 43,000 times per second, and this seems impractical. Should I use a different, lower frequency, and if so, what seems reasonable to you guys?

About the amplifier, I ended up going with a closed loop op-amp, as I can vary the voltage gain at will, what are your opinions about this amp?

 

[audioguru]

An IR LED can easily flash at 43kHz. Any modern opamp can be the receiver's amplifier (don't use a slow old LM324 or LM358).