Would you rather have more outputs or inputs in an ethernet home controller

[blueroomelectronics]

This kit has ethernet & home control in mind, I'm seriously considering 5 (yes five) relays on the design as this would be ideal for a two stage HVAC controller (Furnace & AC). Of course you could use more than one if you need more I/O.

Think of it as a powerful ELK-MM443 controller
**broken link removed**

Well as usual I'm working on the next kit before the last is finished, I like to stir the ideas around before commiting them to a PCB.
The PIC18Fxxxx based kit will have...

• Ethernet ENC28J60
• RS485 (optionally RS232 or possibly RS422) opinions?
• SPI EEPROM
• 32768Hz watch crystal on TMR1
• ICD Inchworm connector

Now here's where I need advice.

Would it be more useful to have 4 relays and 4 inputs?
or 6 relays and 2 inputs
or optoisolated inputs
or analog / digital inputs...

Pictured below is a similar device.
**broken link removed**

 

[dknguyen]

I like inputs personally. But it's more to do with what I do. In robotics, there's only so many motors and actuators you can use, but lots and lots and lots of possible sensors. I just try to make sure I've covered all the outputs I need for actuators first. But for what you are saying it is for, I am guessing you need more outputs than inputs.

But...how about an equal number since you can always use more than one...? Now there's an idea!

 

[3v0]

It seems we often follow different tracks but for what its worth.

You need at least as many inputs as outputs. I favor having more inputs then outputs in that it makes sense to have redundant sensors.

If your budget is 8 I/O pins I would use:
6 pins for relays
2 pins for two 1-wire interfaces to handle inputs.

It is best to have redundant 1-wire networks. That way if a sensor or a run of sensors stop working you can still function.

I am not sure what to say about redundant interfaces. If it were a bare board the end user could populate only the required interface. Not sure about kit form.

I see that Newark has the ENC28J60/SP DIP.

Peter H. Anderson has a selection of Serial Control and Measurement boards using RS232 that you may want to look at.

 

[blueroomelectronics]

Well I do love 1 wire inputs. Now what kind would you like aside from 1 wire?

 

[bloody-orc]

TWI! (or I2C for you PICers)
It actually would be best, if one can get normal Digital outputs also from the board. Like no relay at all, just TTL levels.

 

[blueroomelectronics]

TWI! (or I2C for you PICers)
It actually would be best, if one can get normal Digital outputs also from the board. Like no relay at all, just TTL levels.

I was considering I2C but the MSSP is tied up with SPI (ENC28J60 & EEPROM).