IR remote controller with PIC and 3.6 volts supply

[UroBoros]

Hai All

I have to do a small remote controll transmitter .

Only three commands are required to transmit.

I propose to send 3 distinct IR pulse train of 3 seperate widths.

each command will be a IR pulse of a particular duration. (40khz IR pulse train)

1 key will send a IR pulse train of 500 Usec,
2 key will send 750 Usec
3 key 1ms.

plans to do using 12F629. Will it safely work on a 3.6volts coin type cell with reasonable life?

Any peripheral in PIC to do this easily or any better idea?

Please suggest
Picstudent

 

[petarpav]

PIC and 3Volts?

Hi. PIC12F629 works from 2.0V to 5.5V. You can use delay function of C compiler or timer(if you want precise pulse with)

Best Regards.

 

[VVV]

Re: PIC and 3Volts?

Generally, the IR remote controls use a carrier of about 38kHz.
I suggest you use this aproach, since it is easier to filter out unwanted signals and noise.
Then, modulate this (0-100%) with a code. It is much better than pulse width. Pulse width can change during transmission.

At a minimum, I would send 2 pulses, each of fixed width (say 250us), but make the pause between them variable, like you are proposing. That way, even if the pulse width gets modified during the transmission, the pause between them should not. And the receiver will always ignore pauses that are outside the range you specify. This will provide better immunity.

To save the battery, I would have the micro go to sleep and use wakeup on change to detect a key closure. Once the micro wakes up, just send the pulses and them go back to sleep.

 

[UroBoros]

Re: PIC and 3Volts?

hai
Is it enough to drive the IR TX LED directly from I/O of 12F629 or driving via a transistor is better?

Picstudent

 

[IanP]

Re: PIC and 3Volts?

It should be enough to drive an IR LED directly from the PIC629's pin (with current limiting resistors), as accordingly to the data sheets they should sink and source currents on the GPIOs of up to 125mA.
In order to save the battery try to limit the current to as low as possible ..
Regards,
IanP

 

[VVV]

Re: PIC and 3Volts?

Remote controls drive the LED with a transistor, using very high current pulses, about 0.5A. Yes, 0.5A, but for very short periods of time. There is generally a fairly large cap across the driver. This cap supplies the current pulses.

For your button cell, you should try lowering the current. Anyway, the idea is that you have a lage cap (a few hundred uF) as decoupling cap for the driver. Use 10Ω in series with the battery, to avoid large pulses when you connect it.

So basically the driver is a transistor that drives the LED. In series with the LED you should have a resistor of a few ohms to limit the current. All this is powered from a cap, connected to the battery via a 10 ohm resistor.

 

[metal]

Re: PIC and 3Volts?

Hello picstudent

What language do you use, may be I can help with the code too

Kind day

 

[samcheetah]

Re: PIC and 3Volts?

well, if you are using assembly then go to the IR tutorial from Nigel Goodwin http://www.winpicprog.co.uk/pic_tutorial5.htm

 

[UroBoros]

Re: PIC and 3Volts?

Hai

I am using assembly for the transmitter and C for the receiver.


Let me limit the current as you proposed for led and see how much transmitting range I can acheive within my constraints.

Thanks for the informative tutorial link.

Picstudent

 

[IanP]

Re: PIC and 3Volts?

IR diodes will have Vf of ≈1.8V at 100mA and up to ≈3V at higher currents, so taking into account that you have only 3V supply voltage, you will have to consider several options on how to drive this diode.
I would first try what range can you achieve if you drive the diode directly from PIC's pin.
Also, to further save power, you may consider changing the duty-ratio of the control square wave, but still keeping frequency at 38kHz.
Regards,
IanP

 

[UroBoros]

Re: PIC and 3Volts?

Hai
Reducing the duty cycle seems to be a good option for my purpose.

will test it and will let you know.

I am trying to make a 30 khz squire wave from 12F629 by software.

Suggessions please.

Thanks again

Picstudent

 

[IanP]

Re: PIC and 3Volts?

Have a look at this project:
**broken link removed**
It describes IR beacon based on exaxtly the same PIC, and includes schematic ans ASM code, which can be quite useful for your application..
Regards,
IanP

 

[UroBoros]

Re: PIC and 3Volts?

Hai

I have done the prototype and is under test.

Driving the led directly from PIC pin is not giving required result(In my expiriment)

125ma for PIC is the current it can supply from all pins together.

for any pin only 25 ma is possible.

When I directly loaded the IR led through a low value resistor the PIC becomes unstable.I am using internal RC of PIC.

As I am not having ICD header for 8 pin PICS I dont know what exactly went wrong.
But then I switched the IR led through a transiostor and it is working alright.
After the keypress service I am putting the micro in sleep.
from 3v coin cell I am getting 10-15 feet range.Life of battery is yet to seen!
Thanks for suggessions
PIcstudent