searching GeoJSON features

Question

After googling for many days and reading the OL documentation, I don't understand well how the filterToParams in OpenLayers.HTTP protocol should work, what I'm trying to do is to find and display the GeoJSON features (features stored in my postgis tables) that matches my search using the following code:

Ext.onReady(function() {
var map = new OpenLayers.Map();
var osm = new OpenLayers.Layer.OSM(
    "OSM"
);
map.addLayer(osm);

var mappanel = new GeoExt.MapPanel({
    region:"center",
    height: 400,
    width: 600,
    map: map,
    title: 'A Simple GeoExt Map'
});

var layerList = new GeoExt.tree.LayerContainer({
    text: 'All Layers',
    layerStore: mappanel.layers,
    leaf: false,
    expanded: true
});

var layerTree = new Ext.tree.TreePanel({
    title: 'Map Layers',
    maxWidth: 500,
    region: "east",
    collapsible: true,
    collapsed: true,
    root: layerList
});

var features = [];
var vecLayer = new OpenLayers.Layer.Vector("Results");
var select = new GeoExt.grid.FeatureSelectionModel();

// define the data source
var protocol = new OpenLayers.Protocol.HTTP({
    url: 'http://localhost/postgis_geojson.php?geotable=boreholes_point_wgs84&geomfield=geom',
    params: {
        outputFormat: "json"
//        },
//        filterToParams: function (filter, params) {
//            if (filter.type === name)
//            return params;
//        },
    format: new OpenLayers.Format.GeoJSON({
        ignoreExtraDims: true,
        'internalProjection': new OpenLayers.Projection("EPSG:900913"),
        'externalProjection': new OpenLayers.Projection("EPSG:4326")
    })
});
//    protocol.read({
//        callback: function(r){
//            console.log("received featured: " + r.features);
//        }
//    });

formPanel = new GeoExt.form.FormPanel({
    title: "Place Name Search",
    height: 150,
    region: "north",
    protocol: protocol,
    items: [{
        xtype: "textfield",
        width: 200,
        name: "station__like",
        fieldLabel: "station <br />(use * and . for wildcards)",
        allowBlank: false,
        minLength: 1
    }],
    listeners: {
        actioncomplete: function(form, action) {
            features = action.response.features;
            store.loadData(features);
            vm=map.getLayersByName("Results");
            if(vm.length===0){
                vecLayer = new OpenLayers.Layer.Vector("Results");
                map.addLayer(vecLayer);
                store.bind(vecLayer);
                select.bind(vecLayer);
            }
        }
    },
    buttons: [{text: 'search',
        handler: function(){
            formPanel.search();
        }
    }],
    keys: [{ key: [Ext.EventObject.ENTER],
        handler: function() {
            formPanel.search();
        }
    }]
});

var cols = [ {name: 'station', type: 'string'},
            {name: 'survey', type: 'string'},
            {name: 'type', type: 'string'},
            {name: 'w_depth_m', type: 'float'},
            {name: 'comments', type: 'string'},
            {name: 'latitude', type: 'float'},
            {name: 'longitude', type: 'float'}
        ];

var reader = new GeoExt.data.FeatureReader({},cols);

var store = new GeoExt.data.FeatureStore({
    reader: reader,
    fields: cols,
    autoLoad: false
});
// create grid panel configured with feature store
gridPanel = new Ext.grid.GridPanel({
    title: "Results",
    height: 500,
    region:"center",
    store: store,
    columns: [{
        header: "Station",
        width: 100,
        sortable: true,
        dataIndex: "station"
    }, {
        header: "Survey",
        width: 40,
        sortable: true,
        dataIndex: "survey"
    }, {
        header: "Type",
        width: 40,
        sortable: true,
        dataIndex: "type"
    }, {
        header: "Water depth [m]",
        width: 40,
        sortable: true,
        dataIndex: "w_depth_m"
    }, {
        header: "Comments",
        width: 100,
        align: 'right',
        sortable: true,
        dataIndex: "comments"
}],
    sm: select
});

gridPanel.on('rowdblclick', function(g,rowIdx,r){
    rec = store.getAt(rowIdx);
    map.setCenter(
        new OpenLayers.LonLat(
            rec.get('longitude'),
            rec.get('latitude')),
        10);
});

searchPanel = new Ext.Panel({
    layout: "border",
    region: "west",
    collapsible: true,
    width: 400,
    items: [formPanel,gridPanel]
});
mainPanel = new Ext.Panel({
    height: 600,
    renderTo: "mainpanel",
    layout: "border",
    items: [searchPanel,mappanel,layerTree]
});

});

the code above plot all the features no matter what I write in the search button, so it's not fetching any specific features based on the name I enter.

I think that the PHP script I'm using for the postgis request (update https://gist.github.com/3763701), should allow filtering the features I'm looking for (ie.WHERE ... LIKE ...). This script has a "parameters" option that should give this but so far it only throws an error (here is the reference: http://stackoverflow.com/questions/12591042/parameters-option-in-the-postgis-geojson-php-script).

Sorry for probably this very simple question but I'm just starting using GeoJSON and protocol.HTTP, I'd appreciate your support, thanks