Interfacing IR Remote receiver to a propeller chip.

Martin_H

I did a search for this topic and couldn't find it. I want to interface an IR remote receiver to a propeller chip. I found this page http://learn.parallax.com/node/389 which describes how to do it, but something about it bothers me. You'll notice that the IR receiver is connected to 5 volts and its output pin is connected directly to the Prop BOE's pin. I looked at the Prop BOE's schematic and there's no resistor between that jack and the propeller's I/O pin.

I read the datasheet for the Vishay IR Remote receiver and it looks like there are several versions. Those that requires a 5 volt supply voltage also output 5 volts. So how does this work without damaging the propeller chip?

GordonMcComb

I was thinking maybe the PropBOE has internal resistors, but I don't seem them in the schematic. I'd probably get the wide-voltage versions of the Vishay receivers, and plug them into the 3.3V rail, and then not bother with the limiting resistors. But either way should work.

LoopyByteloose

First off, the IR remote control receivers usually require +5 to operate. I am not sure why the output doesn't have a resistor between the Propeller and the reciever. It may just be a sloppy build. 1K to 10K are adequate to protect the Propeller. I tend to prefer the 1k.

I have used code on the BS2 and that worked very well. I am not sure what is available for the Propeller, but I love using an IR remote for multiple button control.

The resistor may not be necessary due to the output being a 38Khz pulse. That would effectively reduce the overall power of the recievers output.

Phil Pilgrim (PhiPi)

Loopy Byteloose wrote:

1K to 10K are adequate to protect the Propeller. I tend to prefer the 1k.

2.2K is the absolute smallest you should use. The Prop's internal protection diodes are spec'd for a maximum of 500 uA. (5.0V - (3.3V + 0.6V)) / 500 uA = 2.2K. I would use 3.3K or more to be on the safe side.

-Phil

Phil Pilgrim (PhiPi)

Martin,

The reason it's safe to connect the IR receiver directly to the Prop's input is that it's output structure consists of an open-collector driver, internally pulled up to 5V with a 20K resistor. 20K is more than enough to limit the current in the Prop's internal protection diodes.

-Phil

Martin_H

Thanks Phil for solving the mystery. I figured learn.parallax.com wouldn't lead me astray, but an exception to the rules makes me curious. I figure there's an opportunity to learn something.

StefanL38

About the 38kHz Signal:
there are two different types of IR-receivers

the first one does the decoding of the 36, 38, 40 kHz carrier-signal and deliveres the databits that are "modulated" on the 36-40 kHz carrierfrequency
(the databits are "encoded" through different long burst of the KHz signal)
this first type does only work reliable when the frequency of the sender exactly matches with the receiver.

second one is just converting the optical blinking at 36-40 kHz signal to an electrical signal of high and low. So you still have the KHz-bursts. This means the decoding of the bits must be done
by the device this receiver is conected to.

So what type of IR-receiver are you using?

best regards
Stefan

Phil Pilgrim (PhiPi)

The one sold by Parallax does the demodulation.

But among that group, there are still two kinds: those that can produce a continuous output when receiving a constant source of modulated IR and those that time out under the same circumstances. I believe the one Parallax offers is of the latter sort. The ones that don't time out are more rare.

-Phil

Publison

erco has two threads going on discussing the different hardware:

http://forums.parallax.com/showthread.php?142583-IR-Beacon-Tracking&highlight=TSOP4038

http://forums.parallax.com/showthread.php?142217-IR-Receivers-Hoarding-Time!&highlight=TSOP4038