When switching on/off power supply transformer (220/9V 12VA) I got spikes in time interval 0-250 microseconds after switching xformer. Amplitudes were up to +- 5 volts, on the output of 7805, duration up to 1microseconds.

I put 47nF capacitor on primary side of xformer and problem is solved. There is no spikes anymore and my 8052 does not reset anymore when switching power supply.


regards, Damjan