[PIC] Controlling 5 IR emitters using PWM of 16F877A

[adeel.sid]

Controlling 6 IR emitters using PWM of 16F877A

Dear all;

In my circuit I want to operate 6 IR Emitters (all cathodes are common) using PWM of PIC.

I came with idea to use analog deux/demux ic to sequentially operate each IR Emitters but it requires some current drivers since required current is >70mA for each IR emitter.

I came up with idea to use npn transistor with each IR Emitter but looking for some better ideas.

Can anyone guide me how to derive IR emitters instead of using discrete device (transistor)
Also, how can I combine cathodes of three diodes (two groups) after that?

Any suggestion would be appreciated

Regards

 

[KlausST]

Hi,

It's not clear to me. Do you want all six to work at the same time, or only one?

Have you thought of a mosfet.
Paralleling should be done with a resistor on each IR emitter.

It depends on supply voltage, but there are a lot of analog switches with rds-on lower than one ohm.

Hope that helps
Klaus

 

[adeel.sid]

Hi,

It's not clear to me. Do you want all six to work at the same time, or only one?

I want to flash each one by one, let's just say, first d1, then d2, d3 and so on

here is pictorial representation

 

[KlausST]

Hi,

Seems to be a good way.
On the left picture a high voltage activates the led, and on the right side also.

No supply voltage?

There are 1 of 8 decoders with enable input.
Put the pwm on the enable... if i remember right '138

Take care often they have active low outputs

Klaus

 

[techgreed]

You can drive them with a single transistor and a demux IC. Either cathode or anode of all the emitters should be connected together and connect it to the transisitor.Then connect demux lines to individual emitters.

 

[adeel.sid]

You can drive them with a single transistor and a demux IC. Either cathode or anode of all the emitters should be connected together and connect it to the transisitor.Then connect demux lines to individual emitters.

I was thinking of same to derive all (or group of three) with a single transistor.
for example; 2N3904 is 625mW (provide ~625mW/5V=120mA) and in my case, each IR diode requires 100mA.
If three are joined in parallel then current will be divided (120/3=40mA)
Will this scheme work?
could you elaborate your idea as well?
I think I got it:
http://picprojects.org.uk/projects/inf/drivingLEDs.pdf

Didnt I?