I'm with your opinion. Unfortunately the space left on the board is not so much so I think it's impossible to have three screw pins for each input/output. This will raise the required screws from 7 to 15...
Yes I can imagine, space is a big constrain. Your boards are really small, nice.
You're right. Having at least 12V coils is a better solution than using 5V relays. I'm not sure if 12V relays will reduce the overall Amps taken from the DC connector (the current sink from the relays is not related to the voltage but it's something proper to the relay mechanics). Having 12V coils will helps to reduce temperatures on the onboard DC power supply. I'll investigate this solution.
Actually the board is provided with a DC linear voltage regulator with an input voltage up to 20V but it's mandatory to reduce the current drawn by the circuit to be able to run at this maximum voltage.
Yes, the rated current for the coil is bigger for lower voltages. Basically the energy required to act on the relay is the same, so lower voltages are compensated with bigger currents.
For example, if you look at this
datasheet you will found that the 12V coil required almost 60% less current.
I've saw the linear regulator, but my concern is about the overall consumption where more boards will be powered from the same power supply. As you know, with a linear regulator all the exceeding power is converted in heat.
If you will really move to a 12 or 24V relays, the linear regulator shall be integrated with a DC/DC one to lower the voltage without "burn" all the power, otherwise the consumption will not raise down.
The problem of the linear regulator is that if your board require 500 mA @ 5V, the current drawn before the linear regulator is always 500 mA regardless the input voltage. So, if you power at 24V you will "burn" (24-5)*500 mW that means a supply efficiency of 25%.
I know very few components, that tipically I've saw on other boards, Texas Instrument has a DC/DC switching regulator (MC33063ADR) that is small and require some external components, you can find here
This will be sure an option for next board... this one is targeted to RS485.
Nice, if you are willing to revise the PCB take as option the possibility to solder on the rear the RFM22B radio. You will build a bridge and introduce remote radio and other possibility at lower price.
Yesterday I was able to have the prototype working and running with the optiboot bootloader. It's amazing
I'm writing a library to allow users to easily interact with relays and inputs/outputs pins and RS485.
I've attached some pictures of the prototypes.
Are you interested on test it with Souliss project? I have two prototypes in my hands. As soon I'll terminated to test them and to write the library I can send them to you ... What do you think about?
Sure that I will!
In the project agenda there is the support for RS485, that means build a collision advoidance in the software, because Souliss require P2P.
Now the work is focused on two main jobs: including the ENC28J60 in Souliss and the Android client. The first one is carried out by me, and will allow the support of KMTronic DINo boards; the second one is carried out by shineangelic that care of user interfaces.
Is just a matter of time, I hope to end the work for the ENC28J60 in one month and later I could start with the RS485. Let me say that we can agree some dates to get the Souliss support within the market starting date of the board.