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smart Power strip
do you know any smart power strip that could be used with robotank, maybe by opening It and adding a db9 cable or something similar?
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Not for my app, reef-pi will work with some Kasa's. At some point I do plan to explore this. Here's a link to another alternative however you need to add the circuit from the guide.
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american DJ are not available here in Italy.

honestly i don't like the idea to have a Power strip controlled via wifi only. if you loose the connection to the strip, you could make huge damage (in example a pump always on or always off.)
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I agree, hard wired is best. You might have to DIY one or use what I have. You can get relay modules that connect to a Raspberry Pi so it could be connected to a DB9 on controller.
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yours has a strange form factor, i prefere to use the standard outlet available in Italy, much more compact (and easier to replace as they are available in any store)
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Strange lol. Yeah there's a lot of space on the universal bar as the UK plugs are very large. On the US version I added extra space on two outlets for larger AC adapters. Definitely can't beat DIY though. :)
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this is what i like
8 plugs on the left and in the 4 slots on the right i'd like to place the relay board but it won't fit inside

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Yeah looks tight and it's a lot of wires. Maybe two 4 channel modules or eight 1 channel.
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How many power string I can plug to the v2 robo-tank board ? Because using the 4 channel will be easier, but i'll need twice the ports on the board.
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On the base controller you can connect up to 16 relays to the DB9 plugs, this is the same on all of them. Each plug has 8 signals so you would need to split 4/4 for each relay module.
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can i expand this in some way?
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Yeah you can add an additional pca9685, this will add 16 extra outputs.

Adding a 2nd pca9685 will cause a problem in v6.3 though, I have this fixed for 6.4.
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how many pca9685 i can add?
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Technically 64 of them but reality maybe 2-3. The problem is I2C can only support a handful of devices without buffers etc. If you connect multiple you should daisy chain them all together so you create a single line vs a Star pattern. If possible use jumpers under 6" to connect them together. It's important to keep I2C cable very short.
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So, if I understood properly, using one pca9685 i get get 16 power outlet (8 for each DB9 on the pca9685) using only one DB9 on the controller (the one connected to the pca9685)

But what if my relay board only has 4 channels ? Can I connect two 4 channels relay boards to a single DB9 ?

Let's assume I need 16 power outlet but I can just use multiple 4 channels relay boards. Any idea ?
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The DB9's don't have any signals from pca9685, these are all GPIO's from Pi. You can split them up, simply run 4 wires to one relay board and 4 wires to another. Then the same with Ground. Here's a link showing which pins are what on the DB9's.
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Can i daisy chain multiple pca9685 ?
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I'm sorry, I'm sure I replied to this long ago. You can daisy chain multiple pca9685's however it's important to keep wires as short as possible, 1-2" inches would be great for daisy chain and then 3-4" to controller. I2C is very sensitive and limited amount of power so you need to keep external device count as low as possible. Something like this would be good if you start adding multiple devices.
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Cool this is perfect for my kh tester. 1 on this placed near the robotank and the kh tester far away.
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This is the better method but you need a piece at each end. This will send the signal down two lines, when it gets to the other end it compares both signals, if they are exact it accepts them as it's likely a valid reading, if the signals don't match when they arrive it means noise got in so it will discard.
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