Hi, The FoxGM has a buzzer that you can use by sending a square wave to OG5 look at the schematic of the foxgm to see how it is attached and replicate that on your board and then use the example provided to use it changing usDelay to modify the frequency.
http://acmesystems.it/?id=3 The buzzer on that is just a standard PCB mount piezo transducer if that is sufficient then there will be no requirement for a switching transistor. You'd only need it for a larger device like a moving coil loudspeaker. If you do go the loudspeaker route you need to make sure you don't leave the control pin in a high state either during boot or after your buzzer code has run because you will just be stuffing DC though the coil which will do it no good at all. Either that or do some decoupling so that even with the driver transistor in an on state it doesn't just sit there sinking DC through the coil.
