The first two outputs of IC3 (Q0 and Q1) are
connected (ORed) via diodes D1 and D2 to the
base of transistor T1. Initially output Q0 is high
and therefore relay RL1 is energised. It remains
energised when Q1 becomes high. The method of
connecting the gadget to the fan/cooler is given
in Figs 3 and 4.
It can be seen that initially the fan shall get AC
supply directly, and so it shall run at top speed.
When output Q2 becomes high and Q1 becomes
low, relay RL1 is turned ‘off’ and relay RL2 is
switched ‘on’. The fan gets AC through a
resistance and its speed drops to medium value.
This continues until output Q4 is high. When Q4
goes low and Q5 goes high, relay RL2 is switched
‘off’ and relay RL3 is activated. The fan now runs
at low speed.
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