Hi Raj,
Post #17 values look OK to me.
ie:
5V- [ 3*1.2Vfwd]= 1.4V/82R =17mA
5V- [2* 1.2Vfwd] =2.6V/150R = 17mA

Assuming that you are using a 5V source for the LED's.
E

So I will use this value resistors and will use a MOSFET to drive them.
Resistors of 82 ohms and 150 Ohms, MOSFET IRFz44N to drive LEDs.
Please, can you check this circuit for the final time for to be sure before implementing it on PCB?

 

Hi Raj,
Post #17 values look OK to me.
ie:
5V- [ 3*1.2Vfwd]= 1.4V/82R =17mA
5V- [2* 1.2Vfwd] =2.6V/150R = 17mA

Assuming that you are using a 5V source for the LED's.
E

Hi Sir,

I have created the ckt according to the diagram. And supplied power from Arduino 5V. I was checking its working through the camera of my mobile. Then I found that if I use one, not with MOSFET and everything just direct from pin its intensity was higher means it was much brighter than of the this ckt's leds. when I checked the Array LED's pulse through the camera it was very dim (less brightness). can you please help me with this. is this because of the resistors or something?

 

hi Raj,
The N MOSFET Vgs voltage you are applying from the Arduino may be insufficient to turn the FET fully On, ref this clip from the d/s
E

 

hi Raj,
The N MOSFET Vgs voltage you are applying from the Arduino may be insufficient to turn the FET fully On, ref this clip from the d/s
E
View attachment 178527

I have changed MOSFET to transistor now 2N2222 and now it is giving little more than that of MOSFET. But my first three LED's are not blinking. First three from 5V of arduino wire.

 

hi R,
As a test of your LED wiring on the bread board, remove the 2N2222 and connect the wire that went to the Collector to 0V,
so that the full 5v is applied across the the resistor LED network, they all should light.
E

 

hi R,
As a test of your LED wiring on the bread board, remove the 2N2222 and connect the wire that went to the Collector to 0V,
so that the full 5v is applied across the the resistor LED network, they all should light.
E

Connected and checked and found that the first LED was not working that's why it was not glowing. I have changed the 1K resistor to 100 ohms resistor at the base of the transistor but almost same glow pulse.
But how can I solve the Glowing issue? I need more glow when I send a pulse so that It can cover more distance.

 

Hi,
You could increase the LED current to say 20mA or 25mA.
If you want to have more IR light, you should consider higher power LED's.
E

 

Hi,
You could increase the LED current to say 20mA or 25mA.
If you want to have more IR light, you should consider higher power LED's.
E

How can I increase the current? I am using right now is 940 nm.

 

I have changed MOSFET to transistor now 2N2222 and now it is giving little more than that of MOSFET. But my first three LED's are not blinking. First three from 5V of arduino wire.View attachment 178530 View attachment 178531

Hi! It’s hard to see, but one of your LED strings have three resistors in series. Another has two resistors in series. While the last has only one.

I can’t read the color codes, but could you post the total series resistance of those resistors in each LED string? Perhaps the total resistance does not allow enough current to brightly light the LEDs.

To increase current, you perform the calculations performed by ericgibbs, but with resistance as the variable and substituting the higher current in the equation. I.e., for a 20mA current,

(5V - 3*1.2V) / R = 20mA
1.4 / R = 0.02
R = 1.4 / 0.02
R = 70Ω​

Or similarly for a 25mA current (if the LED is rated for 25mA or more),

(5V - 3*1.2V) / R = 25mA
1.4 / R = 0.025
R = 1.4 / 0.025
R = 56Ω​

 

Hi! It’s hard to see, but one of your LED strings have three resistors in series. Another has two resistors in series. While the last has only one.

I can’t read the color codes, but could you post the total series resistance of those resistors in each LED string? Perhaps the total resistance does not allow enough current to brightly light the LEDs.

To increase current, you perform the calculations performed by ericgibbs, but with resistance as the variable and substituting the higher current in the equation. I.e., for a 20mA current,

(5V - 3*1.2V) / R = 20mA
1.4 / R = 0.02
R = 1.4 / 0.02
R = 70Ω​

Or similarly for a 25mA current (if the LED is rated for 25mA or more),

(5V - 3*1.2V) / R = 25mA
1.4 / R = 0.025
R = 1.4 / 0.025
R = 56Ω​

IR LED's are rated 20mA so I can use 70ohms. The total resistance in the circuit is about 314 ohms at IR LED's side and at transistor 100 ohm from base to pin 3.

I have placed 57 ohms in series of 3 IR's and 100 ohms instead of 104 in series of 2 IR's.

 

IR LED's are rated 20mA so I can use 70ohms. The total resistance in the circuit is about 314 ohms at IR LED's side and at transistor 100 ohm from base to pin 3.

So with 314Ωs in the LED strings, you’re going to be supplying only 4.5mA. They are not going to be their brightest.

I = (5V - 3*1.2) / 314Ω
I = 1.4 / 314
I = 0.0045
I= 4.5mA
​

Hopefully, it should be obvious that you need the lower resistance we calculated in series with the LEDs. Also, I’m not sure, but it looks as if you have one string consisting of only two LEDs. These calculations would need to be done with 2 instead of 3 LEDs fir that strings required resistance.

Just to check, let’s calculate the required base resistor for 20mA. Total current the transistor needs to switch is 60mA. Three strings each needing 20mA. Using the rule of thumb that the base resistor should provide 1/10th of the current, you need to calculate the needed resistor value. Assuming a 0.7V drop in the BE junction of the transistor, we get the following,

R = (5 - 0.7) / (60mA / 10)
R = 4.3 / 0.006
R = 716Ω​

It’s inefficient, but you can supply a higher current. With 100Ω, the base sees 43mA.

 

So with 314Ωs in the LED strings, you’re going to be supplying only 4.5mA. They are not going to be their brightest.

I = (5V - 3*1.2) / 314Ω
I = 1.4 / 314
I = 0.0045
I= 4.5mA​

Just to check, let’s calculate the required base resistor for 20mA. Total current the transistor needs to switch is 60mA. Three strings each needing 20mA. Using the rule of thumb that the base resistor should provide 1/10th of the current, you need to calculate the needed resistor value. Assuming a 0.7V drop in the BE junction of the transistor, we get the following,

R = (5 - 0.7) / (60mA / 10)
R = 4.3 / 0.006
R = 716Ω​

It’s inefficient, but you can supply a higher current. With 100Ω, the base sees 43mA.

I have placed 57 ohms in series of 3 IR's and 100 ohms instead of 104 in series of 2 IR's. And placed a 100 ohms resistor at Base of transistor.

 

I have placed 57 ohms in series of 3 IR's and 100 ohms instead of 104 in series of 2 IR's. And placed a 100 ohms resistor at Base of transistor.

Can you post the datasheet or a link to the IR LEDs? The 104Ω resistor gives you 25mA; a 100Ω resistor gives you 26mA.

What happened when you made the changes?

 

Can you post the datasheet or a link to the IR LEDs? The 104Ω resistor gives you 25mA; a 100Ω resistor gives you 26mA.

What happened when you made the changes?

It was running without any problem. I don't know the technical name of this type of LED so can't provide datasheet.
IR led is of white color and 940nm.

 

hi Raj,
This is the circuit diagram in your opening post, I have added the resistor you are now using. [the current in each path is approx 25mA]
You said that the LED Vfwd was 1.2V at 20mA, also 940nm radiation is IR , but you say they are white LEDs.???

E

 

hi Raj,
This is the circuit diagram in your opening post, I have added the resistor you are now using. [the current in each path is approx 25mA]
You said that the LED Vfwd was 1.2V at 20mA, also 940nm radiation is IR , but you say they are white LEDs.???

E
View attachment 178545

I have changed MOSFET to transistor 2N2222 with base 100 ohms instead of 1K and White LED's Means They are Transparent LED's Below is the pic of IR LED I am going to use :

https://images-na.ssl-images-amazon.com/images/I/51f+ibl-5xL._SX342_.jpg

Right now I am using is this one :

https://static.rapidonline.com/catalogueimages/product/s49-4513p01wl.jpg

 

Hello,

Do you have a link to the product at rapidonline in stead if the imagelink?

Bertus

 

hi Raj,
I see, for White you mean 'Clear' LEDs' OK.
I cannot get your rapid link image, it shows error.

E

 

Hello,

@ericgibbs , this is the image posted:



Bertus

 

Hello,

Do you have a link to the product at rapidonline in stead if the imagelink?

Bertus

I have bought them from a store and they didn't specify it's technical name and all just said 940 nm IR LED. below is the Amazon links where you can get the idea from the image what LED's I am talking about:

Here's the link for Clear IR LED:

https://www.amazon.com/Infrared-Lighting-Electronics-Components-Emitting/dp/B01BVGIZGC/ref=sr_1_4?crid=14RQ8D6I5Y6C6&keywords=940nm+ir+led&qid=1559224436&s=gateway&sprefix=940nm+IR+,aps,397&sr=8-4