Input

RustyH

Senior Member
Morning All,

I'm going to be using some IR sensors to input in to an 18M2. These are pre built devices which output around 3v when activated. What type of circuit do I need to use such an input device? Do I need any drop down resistors or anything?

Thanks
Russ
 

Andrei IRL

Senior Member
I am only novice user but i might help.

Picaxe can take up to 5v as a digital input.

So as long as your IR Receiver shares same ground with picaxe you can connect the IR output 3V pin directly to PICAXE input pin.

To privent PICAXE pin from "floating"/getting a faulse HIGH reading you'll need to connect PICAXE input pin to ground VIA 10K resistor.
 

AllyCat

Senior Member
Hi,

It's generally recommended to put a resistor in series between any output and a PICaxe input pin, just in case the input pin gets "accidentally" set as an output. Any value over a few hundred ohms will "protect" the chip(s), but something between 1k and 10k will normally be "best".

If the "pre-built devices" are a commercial product, then it's usually worthwhile to quote the type number, or better a link to their data sheet. Not all "3 volt outputs" are the same and it may help us to tell if you need a pull-down (or pull-up) resistor. But you almost certainly do NOT want a "drop down" (potential divider) resistor directly on the PICaxe input.

Cheers, Alan.
 

westaust55

Moderator
A link to the data for the IR sensors would be helpful - to ascertain if open collector output, etc.

The M2 and latest X2 PICAXE parts can be operated down to 3 V so are you in a position to operate all parts at the lower voltage?

PICAXE inputs can accept signal up to their supply voltage without promlems.
 
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