Components for Infra-Red comms

[jedynakiewicz]

I am rather confused by three conflicting circuit diagrams relating to wiring the infra-red receiver to PicAxe chips.

Picaxe Manual 2 (page 112) shows pin 3 connected to 0V by a 4.7uf capacitor and pin 1 to 5V via a 4k7resistor.

Page 3 of document axe040 shows pin 3 connected also to 5V through a 330R resistor.

Page 7 of document AXE091 (my development board) shows a third variation with no capacitor but with both resistors!

Which is the correct - or perhaps optimum - circuit diagram?

A further question; I have an idea that the resistors +/- the capacitor are placed optimally close to the IR receiver if the receiver is a distance from PIC. I need to mount the IR receiver perhaps some 5-10 cm. from the PIC; would I be okay with the other components on the board with the PIC or should I use a daughter board with the resistors and capacitor next to the IR receiver?

Advice would be appreciated.

 

[Dippy]

Hi,

I guess you are very new to electronics?

(Manual2 page 112).
On that IR device Pin 1 is the signal output pin.
The resistor connected between it and +5V is what's known as a 'pullup'.
i.e. because the output of the IR receiver can only drive low it tends to float around when not being driven.
So, this ensures a good clean up-down (on-off or high-low) signal when it receives a valid IR signal.
(It should be noted that many IR receivers have this 'pullup' built-in.)

Pin 2 is the ground and connects to 0V and is also connected to PICAXE gnd/0V.
This is the same in all three examples.

Pin 3 is the +V supply. Quite often a capacitor is put between this pin and Gnd to suppress any noise on the +5V line. It doesn't short the DC supply voltage. I would include it.

In your second reference a 330R resistor has been added (in series) to the supply to Pin 3.
This in conjunction with the capacitor acts as a filter and will improve the device's 'rejection' of noise.
I don't know if that 330R value is ideal, I can only assume it's been tested.

Yes, the third reference has dropped the capacitor.(?)
In some cases it may not be needed, but if you are putting your receiver some distance from the PICAXE then I would ignore this version and add the capacitor.

Have a look at the MANUFACTURER's data sheet as they often give clearer information.
There are DOZENS of similar products.
have a look at this:-
http://sharp-world.com/products/device/lineup/data/pdf/datasheet/gp1ux51qs_e.pdf
Look at the Internal block diagram.
See the transistor?

As an aside; always add a capacitor across the PICAXE power pins. Not always needed but it will almost always improve performance. (PICs generate noise).

 

[jedynakiewicz]

Not so new to electronics...just a little frustrated by three differing versions of apparently the same diagram within the picaxe documentation - and then not thinking it through properly!

Thanks for the clarity of the explanation - very helpful and concise; as well as rather unexpected at 23:00 on a Sunday evening!

 

[westaust55]

Keep in mind that this is an international forum with members on all continents and many islands so if you are lucky there may be some response at any time.

In the same manner it can be wise to avoid local slang which may confuse members from other parts of the world.