The relay coils had 1N4004 diodes across them to catch the back EMF when they switched. Initially, all looked good, but when we tried one of the inputs, the 24V supply current limited and the voltage ...

Using N-Channel MOSFETs to switch AC, sensing temperature changes with signal diodes, and even replacing a 555 with a blinking LED are just a few of the hacks covered in the video below the break.

As shown in part b of the figure, there's a red LED and reverse 1N4004 diode in series-parallel between pin 6 of the MOC3011 optotriac driver and the MT2 pin of the 2N6075A power triac.