• Pure coincidence but I was working with an MRP121 keyboard on an Espruino MDBT42Q using the interrupt method. The interrupt is actually active low and hence needs a falling edge detection on the setwatch() function. Also the direct connection of the interrupt to an Espruino pin needs the internal pullup resistor enabling. Here is a working snipet to see the approach.

    // Setup pins and interface to MPR121
    const sclPin = D15;
    const sdaPin = D14;
    const irqPin = D16; // interrupt from MRP121
    // IRQ is Active Low, open Drain (ref datasheet) - make use of internal pullup 
    // connect to MRP121 via Espruino MRP121 library
    function mprConnected() {console.log ("MPR121 Connected");}
    var mpr = require("MPR121").connect(I2C1, mprConnected , { address: 0x5B});
    // define function for interrupt (fires on touch AND release)
    function touchedIRQ() {
            //console.log ("debug - interrupt received");
            var keys = mpr.touched();
            if (keys != 0) {console.log("Touched: " + keys);}
    // watch the irqPin and fire the interrupt function on capacitance change
    // IRQ is active low, so trigger the interrupt on a 'falling edge'
    if (setWatch(touchedIRQ,irqPin,{repeat:true­, edge: 'falling'}) === 1) {
      console.log( "MPR Interrupt Enabled" );
    else {console.log ("error - set watch on interrput pin NOT enabled"); }

    Also Note the MPR121 keyboard im using does not have pullup resistors for the I2C: SCL and SDA, so I have added a 4.7 K resistor on my prototype board between each of: sclPin and 3.3v and sdaPin and 3.3v , I believe some MRP121 breakout boards already have these.

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