This is a design circuit that Atmel recommend that a diode is fitted between Reset
and Vcc as shown here, but we have not found it necessary in practice. Note
their recommended resistor and capacitor values are slightly different, but
these values are not critical. A capacitor between 10nF and 100nF and a
resistor between 4K7 and 10K will be fine. This is the figure of the circuit;
