I was thinking about extensions for this board:

• SSR relay board that can be directly connected to the boxed header IO's. The IO header is already compatible with a relay board on aliexpress (10 USD for 16 channel relay board, https://www.aliexpress.com/item/DC-5V-12V-16-Channel-Relay-Module-Interface-Board-For-Arduino-PIC-ARM-DSP-PLC-With/32501824575.html). But I like SSR relays, so I will replace the normal relay board with the SSR board later. The SSR board will cost more. That's the downside. 10USD for a 16 channel relay board with free shipping is cheap. Optocouplers are on the relay board, so it can be connected directly with a ribbon cable.
• Input board with opto couplers and/or DC filters
• Analog inputs (with external I2C). I bought some cheap PIR sensors at HornBach. I will modify them with a separate PIR (logic output) and separate ambient light output (analog). Analog signals are not good in probably a noisy environment and/or with long cables. A good way to measure this over a distance would be to convert the ambient light sensor voltage to a current with an opamp. On the other side is a low pass (DC) filter with a precision resistor. This resistor will convert the current to the voltage again and this (ambient light) voltage can be measured with a x channel I2C ADC. The PIR output can be directly coupled to an IO (maybe a small DC filter). The PIR modification will be another project. Modification is necessary to use the same PIR as an alarm sensor when you are away (also during the day, so separate light and PIR!) and you can use the same sensor at night to switch on the lights when you are at home.

Leave a comment for requests and/or suggestions