There are four 0.1uF capacitors in the circuit that are not shown on the schematic. One is located on the output from the 78L05, another is on the output from the 7812, another one is on the power pins right at the PIC and the last one is located right beside the OP-Amp.
The 22uF are there to keep the PIC inputs from cycling on and off caused by the AC voltage used for the inputs.
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