IR Transmitter

Hi,

I want to turn on and off of mosfet through shift register and the IR led is connected to output of the mosfet. In normal condition when mosfet is off,IR led gets conducting. When mosfet is on,IR led gets off.
i am Connecting 4 IR led in series with 12v powersupply and maintaning 100ma throughout the circuit.
help me to find schematic and explanation for this

In normal condition when mosfet is off,IR led gets conducting. When mosfet is on,IR led gets off.

Would it not make more sense if a conducting mosfet switches the LEDs on and a non-conducting mosfet switches the LEDs off? If not, please provide more details of your project.

In that case, you can simply invert the control signal to the mosfet, either by means of an inverter between the shift register and the mosfet or in software.

Hi,
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.

Can you please post your code?

Look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks.. Tom... :slight_smile:

Need to know the circuit to control the mosfet

Please refer the block diagram i have attached.Need to find the circuit for mosfet

mosfet.jpg

Hi,
Thanks for the diag;
OPs diag.
mosfet.jpg
So you have a series string of IR LEDS, and you want to control each LED ON or OFF.
Because each LED is at a different and changing potential depending on how many LEDs you want ON, opto-coupling between the 595 and each MOSFET may be the answer.

Tom... :slight_smile:

Hi,
This is a circuit I have just drawn, it is not tested.
Feel free to edit, comment, criticise. :slight_smile:
Outputting a HIGH from the 595 to an opto will turn that particular LED OFF.


Tom.. :slight_smile:

A switchable constant current source can be built from a npn transistor and an emitter resistor. Input from a digital output pin to the transistor base, and output from the collector to an individual IR or other LED, or multiples for a brighter beam. One such circuit for each LED is cheaper and simpler than the suggested circuit with a common constant current source.

DrDiettrich:
A switchable constant current source can be built from a npn transistor and an emitter resistor. Input from a digital output pin to the transistor base, and output from the collector to an individual IR or other LED, or multiples for a brighter beam. One such circuit for each LED is cheaper and simpler than the suggested circuit with a common constant current source.

I agree a simpler control circuit, but OP may have a particular reason for series LEDs.
Four individual LEDs and a current source = 4 * 100mA == 400mA.
Tom.... :slight_smile:

12V and 100mA make 1.2W continous power consumption. In the switched source mode current flows only while a LED is on.

Thank you so much for ur replies. Can you please explain the circuit?? and also i want to maintain 100ma throughout the circuit. I am going use this as IR transmitter 4 group of 4 led in shift register(daisy chain) and communicate through serial communication

Thanks

I described my simple circuit in #7.

Can u please explain the circuit u have drawn??

Thanks Tom

Hi,

I am going use this as IR transmitter 4 group of 4 led in shift register(daisy chain) and communicate through serial communication

So you have 4 groups of 4 LEDs, do you want to turn each LED ON independently or a group at a time.

  • What is your project about?
  • What is the application?
  • Can you tell us your electronics, programming, arduino, hardware experience?
  • Is this a school/college/university project?
  • Do you know how the 595 works?
  • Do you know how an opto-coupler works?
  • Do you know how a MOSFET works?
  • Have you written any code?

Thanks… Tom… :slight_smile:

This is my school project. I am learning electronics and Embedded C. My project is to built IR transmitter and frequency with 56 khz frequency

VanathiPrakash:
This is my school project. I am learning electronics and Embedded C. My project is to built IR transmitter and frequency with 56 khz frequency

  • What will you be transmitting IR, digital signals?
  • Why do you want to switch each IR LED on independently?
  • Can you just turn them ON and OFF all at once at 56kHz??

Thanks... Tom... :slight_smile: