Crystal +---()---\ NC | 1 14| +5V | 2 13| | 3 12| | 4 11| | 5 10| | 6 9| Gnd | 7 8| Output \--------/ (top view!) function: Generate clock signal package: DIL14 (sort of) manufacturer: All kinds comment: Rectangular metal box Have a look at the scope (if you've one). It should have a "1" of Vdd - 0,5V and a "0" of GND + 0,5V. As far as our teacher told us, the "usual" crystals with two pins are only frequency filters and this ones are frequency generators, which really "produce" AC of the specified frequency. Sebastian Willing Indeed it is a crystal plus electronics with a TTL- or CMOS- compatible output level. Paul B.