Capacitor size

Hi,

I have a simple circuit with a PICAXE that controls a relay board, when the relay board is empty it works fine.
But when I put a simple 20W lamp on one of the relays (230Vac) the chip resets very often when that relay starts/stops.

I have a 0.1uf on the power legs of the IC, how do I know what other size is needed to prevent it from resetting.
I didnt make the relay board myself, but from what I can see there is no caps on the board.

The relays use 12V where the IC is using 5V.
The 12V is from the powerinput, the 5V is from a 7805.

Does the reset pin need a cap?
What about the extra 0V pin the chip has (Picaxe 28X1, theres a pin next to serial connection with 0V, although both 0V and VCC is on the other side too).


/Jan
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