2
\$\begingroup\$

I've designed the following IR remote control circuit. I need to put 2 LEDs on it so I can physically, simultaneously point the remote at my wall mounted TV and my VCR, etc which is all situated much lower down.

I am planning to put these LEDs in series with no current limiting resistors given the voltage drop of 1.5V across each. I think this is more efficient than having them in parallel as each will then need a resistor.

I'm not regulating any voltage from the cells as the diagram shows. I've set the fuses on the MCU accordingly and the crystal running it is at 8MHz (not shown). I will probably turn off the brown-out detection fuse so that this can run ok as the voltage from the cell slowly depletes.

My question is, is there anything problematic with this design? Will there be any frequency related problems with running an IR remote protocol at 38kHz? Is setting up the LEDs in parallel going to give any advantage that more than offsets the power loss that would result by then having to include current limiting resistors?

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
0
\$\begingroup\$

Your circuit is fine. It's the same circuit which is used in hundreds of millions of commercial remote controls, and they operate for at least 15~20 years. You could use a series resistor (and place LEDs parallel), but you'll decrease the operating range.

In case you want to use the RC-5 protocol: the old remote controls used a 50% duty cycle for the modulation. With the use of microcontrollers that has been reduced to 33% or even 25%. Neither is a problem for the AVR. Shorter duty cycles make your batteries last longer.

\$\endgroup\$
0
\$\begingroup\$

The better IR LED's in 5 mm are 1.2V @50-100mA so you can expect better efficiency using these with 10 Ohms in series with 2 for insurance and current shunt. Parallel use of LEDs is a waste of <50% effciency.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.