public function __CONSTRUCT()
{
    try
    {
        $this->pdo = new PDO('mysql:host=localhost;dbname=deimos1;charset=UTF8', 'root', '');
                    $this->pdo->setAttribute(PDO::MYSQL_ATTR_INIT_COMMAND, "SET NAMES 'utf8'");
                    $this->pdo->exec("SET NAMES 'utf8';");
    }
    catch(Exception $e)
    {
        die($e->getMessage());
    }
}

public function Obtener($acronimo) {
    try {
        $stm = $this->pdo->prepare('SELECT * FROM categoria WHERE acronimo = ?');
        $stm->execute(array($acronimo));
        $r = $stm->fetch(PDO::FETCH_ASSOC);

        $alm = new Categoria();

        $alm->__SET('acronimo', $r["acronimo"]);
        $alm->__SET('categoria', $r["categoria"]);

        return $alm;
    } catch (Exception $e) {
        die($e->getMessage());
    }
}

$r = $stm->fetchObject(PDO::FETCH_OBJ);

<meta http-equiv="Content-Type" content="text/html"; charset=utf-8"/>

$pdo = new PDO("mysql:host=localhost;dbname=DB;charset=UTF8");

<?php
$dsn = 'mysql:host=localhost;dbname=testdb';
$username = 'username';
$password = 'password';
$options = array(
    PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
);

$dbh = new PDO($dsn, $username, $password, $options);
?>

$alm->__SET('acronimo', $r->acronimo);
    $alm->__SET('categoria', $r->categoria);

$r = $stm->fetch(PDO::FETCH_ASSOC);

$alm->__SET('acronimo', $r["acronimo"]);
    $alm->__SET('categoria', $r["categoria"]);