I anticipate having all the parts in any kit.
I have a bunch of each relay, so I'll just use them up. I also have a number of the HC-SR04 modules. The Chinese, in a rare fit of generosity, sent me a duplicate order for six of them out of the blue, so I have more than I anticipated having. I also put in an order for eight more from AliExpress so I had enough for all the remaining boards. The other components that were not readily available or too expensive are also coming from AliExpress.
The relays are simply a set of FORM-C contacts that are totally isolated from any circuitry on the sensor board or it's power. You can obviously wire it just like any other ITAD type sensor for common signals. For the ones I make and keep, I'll probably use the 10A relays to give me maximum flexibility in their deployment. The 3A relays have lower coil currents, so for signals they are probably a slightly better choice.
