OK, you asked a lot of questions. I don’t think I can answer all of them at once, so let me start with some:
– In case you haven’t checked this out, we have a table that compares our main OpenSprinkler products:
https://opensprinkler.com/faq/#technical
– The ‘Arduino-based’ OS refers to the microcontroller-based OS (current version is 2.3, either AC or DC version).
– The built-in relay has been discontinued on all OS products. If you need to use a relay, you can follow this blog post:
https://opensprinkler.com/using-24v-ac-relays-with-opensprinkler/
to get a 24VAC relay and connect it to OS externally. 24VAC relays are pretty inexpensive.
– OS DIY kit has been discontinued. We recently bought back a small batch of DIY 2.1u kits from MicroCenter (because MicroCenter does not want to carry discontinued products), that’s why there are a few made available you can purchase on http://rayshobby.net/cart. There are only a few kits left, and once this is gone, there is no more DIY kit.
– OSPi has a built-in PCF8591 4-channel ADC, which you can use to interface with analog sensors.
– It’s possible to connect both a 433MHz transmitter and receiver. Just solder some wires from GPIO pins. You do need to modify the source code to customize your need. The board has mapped out three pins to fit a transmitter, because the OpenSprinkler firmware supports radio-frequency stations. I am not sure why you would want to connect a receiver, but as I said, you can always solder some wires to connect external components. The firmware is open-source and you can modify it anyway you want.