Be careful using your micro that you take particular care with the board design, casing, and earthing to prevent stray RF from being emmitted (esp at harmonic levels)

I had to fault find a design once where the product worked fine, (had a 8051 driving a voice chip where the siren tone was recorded, and drove the lights ... blah blah) however the PCB design radiated RF all over the place and this interfered with the VHF radios in the vehicles, (-100 to -80dBm so enough to unmute the radios) in the end it was a redesign of the board, the casing, and the control head - used to change the siren tones.

Regards

Marshall