Few Questions about Sound on Light

[Electro132]

Need help with IR LED design

Hi

I need some help with this circuit design.

i am trying to build this circuit so then the current can go through it and out through the IR LED. It is attached. I need to know if something is wrong with it as i was advised that it needs its own source of power for it to work but i found out that you could use the usb port of a laptop or computer to recharge the device.

Any help is appreciated, thanks

 

[Electro132]

Breakdown is the normal mode of operation of a zener diode.

Thanks Harald.

Just wondering, can this circuit do without a power source and just uses the power of a laptop or desktop instead?

 

[(*steve*)]

Well, you can get 5V from the USB ports of a PC. A change in the resistor value in series with the LED could be used to set the current at 20mA (or whatever)

Then the speaker output could be used to modulate the light intensity as in the example above.

It is quite likely (but not 100% certain) that the ground terminal of the USB is common with the ground terminal of the speaker output.

 

[Harald Kapp]

Electro123: Please do not create a new thread if there is already one open with the same question and from you, too.

I merged the two threads into this one.

 

[Electro132]

Electro123: Please do not create a new thread if there is already one open with the same question and from you, too.

I merged the two threads into this one.

My apologies Harald, i didn't know they were combined but i will post on the one thread from here on. Thanks

 

[Electro132]

Well, you can get 5V from the USB ports of a PC. A change in the resistor value in series with the LED could be used to set the current at 20mA (or whatever)

Then the speaker output could be used to modulate the light intensity as in the example above.

It is quite likely (but not 100% certain) that the ground terminal of the USB is common with the ground terminal of the speaker output.

Do you think 50 mA or 100 mA is too much? Because I'm thinking 20 mA is too little and might not be able to even power up the LED bright enough. I've attached an updated image.

 

[(*steve*)]

It depends on what you LED is rated for. 20mA continuous current is typical for a normal LED.

I presume you realise that what you're working on will demonstrate the ability to transmit sound on modulated (by intensity) light, but that the range will be perhaps a couple of cm and then only in a dark or dimly lit environment?

edit: what have you done to the circuit? Whay is that diode there? What has happened to the capacitor? What is that thing connected to ground between the diode and the 220 ohm resistor? Just go back to my original design and forget the extra diode since you're using a low power amplifier (it's only going to be needed if you use something much higher powered)

 

[Electro132]

It depends on what you LED is rated for. 20mA continuous current is typical for a normal LED.

I presume you realise that what you're working on will demonstrate the ability to transmit sound on modulated (by intensity) light, but that the range will be perhaps a couple of cm and then only in a dark or dimly lit environment?

Yes that is true and correct. Also to get a larger range for this i would have to get an antenna circuit right? And depending on how high the freq is depends on how far the sound will travel.

edit: what have you done to the circuit? Whay is that diode there? What has happened to the capacitor? What is that thing connected to ground between the diode and the 220 ohm resistor? Just go back to my original design and forget the extra diode since you're using a low power amplifier (it's only going to be needed if you use something much higher powered)

Well i read that an electrolytic cap is used to filter supply rails, for coupling audio signals and in timing circuits. Since i was transmitting sound i thought it would suit it. Btw, did you have MKT polyester Cap or ceramic cap in your design? I know ceramic are often used in RF and filter circuits but just wanted to make sure. I'm guessing its MKT caps.

The thing between the diode and the 220 ohm resistor is a polarised 0.1 uf cap with positive and negative leads. Hey i'm thinking of powering this up with a USB cable. Do you think it's possible? The laptop usb port gives out about 5v. I've done the calculations and it needs a 33 ohm resistor - well actually 30 ohm resistor if there is one.

I've attached the design with the original. Thanks

 

[(*steve*)]

Also to get a larger range for this i would have to get an antenna circuit right? And depending on how high the freq is depends on how far the sound will travel.

No, and No.

You can't build an antenna for light.

Btw, did you have MKT polyester Cap or ceramic cap in your design?

It's pretty much irrelevant.

The thing between the diode and the 220 ohm resistor is a polarised 0.1 uf cap with positive and negative leads.

Practically, these don't exist (they'll be non-polarised), and you wouldn't want one there anyway.

Hey i'm thinking of powering this up with a USB cable. Do you think it's possible?

That's what I assumed you were doing.

The laptop usb port gives out about 5v. I've done the calculations and it needs a 33 ohm resistor - well actually 30 ohm resistor if there is one.

What colour LED are we using again? It would be about 160 ohms for a red LED, and 85 ohms for a white LED at 20mA.

edit: 77 ohms. 3.7V / 0.05A

 

[CocaCola]

You can't build an antenna for light.

 

[Electro132]

What colour LED are we using again? It would be about 160 ohms for a red LED, and 85 ohms for a white LED at 20mA.

Is this just to know if there is voltage coming through for the power source only? Because i thought we were using an IR LED at 50 mA which was blue/purple in colour. But i would choose a white LED.

edit: 77 ohms. 3.7V / 0.05A

Ok will do. Also just checking that the protection diode in the diagram is attached to the A and K of the IR LED? And that the K is connected to the negative line along with the other end of the amplifier attached?

 

[davenn]

LOL CC good one

I was actually thinking of my telescope and its nice sized parabolic mirror

Dave

 

[(*steve*)]

I was actually thinking of my telescope and its nice sized parabolic mirror

You realize he's now going to ask for the correct size wire to make a refractive reflector now, right?

I'll point out that both methods you've illustrated are devices to focus light, they're not actually antennae.

If we want to get pedantic, Electro123 is after this.

 

[Electro132]

Lol hey cmon give a brother a break.

Anyways i've drawn up another one and it shows a VR restricting the voltage coming through from the power source. Please see the image i've attached.

Thanks

 

[(*steve*)]

Why do you keep adding stuff?

Does this look even better?

 

[Electro132]

Why do you keep adding stuff?

Does this look even better?

Ok let me explain even though you probably know it. The diode not the Zener, is used to make sure the current is only going in one direction and not back to the battery. Also the switch makes sure the battery doesn't get used up too much. The Voltage regulator is there because the shop i go to couldn't provide a proper 5 v battery holder though i could of used a 3 v one. Probably for next time. Instead i have to use a 6 volt battery holder.

So how come you added all those extra's in?

 

[dietermoreno]

Haha No actually i work. This is my down time.

Just curious, but then why is this in the electronics homework help thread if it is not an electronics assignment?

Hello and welcome to Electronics Point! The Homework Help forum has been created to allow students to obtain assistance with their electronics assignments. We won't be providing answers to questions posted here, but we can help you work through the problem - helping you to learn.

Please make sure you read this FAQ before posting any thread in this section. Your question is likely to go unanswered if you do not follow these guidelines.

 

[(*steve*)]

Voltage regulators have at least 3 connections, not 2. The switch should come before the regulator. The diode is almost certainly not required. The regulator is also almost certainly not required (just select a resistor based on the voltage).

Look, you need to build the simple circuit I gave you. This is not a practical circuit. It is one that will demonstrate the concept.

If you're having so much trouble getting to build something so simple...

 

[Electro132]

Voltage regulators have at least 3 connections, not 2. The switch should come before the regulator. The diode is almost certainly not required. The regulator is also almost certainly not required (just select a resistor based on the voltage).

Look, you need to build the simple circuit I gave you. This is not a practical circuit. It is one that will demonstrate the concept.

If you're having so much trouble getting to build something so simple...

Ah ok thanks. But i will build the simple circuit as i 've found my missing 3 v battery holder.
I'll let you know how i get on. Cheers

 

[Electro132]

Just curious, but then why is this in the electronics homework help thread if it is not an electronics assignment?

It was combined with another thread by Harald Kapp, one of the Super moderators/moderators......