The Industrial Raspberry Pi Forum

I almost dare not ask this question, because for some reason it feels like there is a very obvious reason. But I don't understand why the DI and DO modules only use 16 out of the 28 present ports for input / output.

Why doesn't a DI / DO just use all 28 ports for input / output?

What is the advantage of a dedicated DI or DO module at 16 ports over a DIO module that uses all 28 ports? With only 2 fewer inputs than a DI and 2 fewer outputs than a DO, a DIO seems like a much more cost-efficient module. But this is exactly why I think this is a dumb question because there obviously must be a reason for the DI and DO modules existing with only 16 ports.

The key point here is that we wanted to have a balance between costs and benefit. We first designed the DIO module. Then with a working DIO module it is reasonable that DI and DO modules are just variants of a DIO. So with this way we save development costs. Therefore if you only want inputs the DI is much cheaper than a DIO module.

Sorry, but I disagree. Looking at shop prices, they are only marginally cheaper. Considering a RevPi setup can be a maximum of 10 modules, I doubt using DI+DO modules over DIO modules is more cost effective.

Regardless of costs, are there plans to produce 28 pin DI and DO modules eventually or is this not cost effective for KUNBUS?

If you are planning a mixed IO system with inputs and outputs then you should always use DIO modules because the cost per channel is less than with DI/DO combinations.
But there are people out there, who only need inputs or who do need much more inputs than outputs. Those people can save over 20% (119 instead of 149 Euro plus additionally 2 channels) if they use DI instead of DIO.
Actually we do not have plans to design and sell 28 channel DI modules. This is all a question of cost per channel and without a huge request from market we could end up with a 28 channel DI module for over 200 Euros which would have a cost per channel too close to two DI modules. I hope you may understand that we cannot further discuss such questions publicly but we will take your inquiry as a signal from market that there is a request for such modules. However if you do have need for larger volumes please get in contact with sales@kunbus.de

I understand we can't discuss this at length. I agree this is largly due to cost-effective pricing on your end, but like you said yourself: for anyone needing both inputs and outputs, there really is no benefit of using dedicated modules when DIO is much more cost-efficient. Thanks for explaining.