12 input pulse counter idea

A while ago now Glyn and I worked on a design for a 12 input pulse counter, we where doing some work at the Centre for Alternative technology, a stripboard version was built and is in continued use monitoring grid import/export, chp and diesel generator (the last two not actually in active use).

We wrote up about it here:

After visiting CAT again recently and discussing a project they hope to do, it got me thinking again about the 12 input pulse counter. In non-domestic buildings that already have pulse output meters on many of the circuits and a meter room with all the meters in one place, a multiple input pulse counter may be the most effective way to add automatic meter reading.

I've wanted to make a PCB for the 12 input pulse counter for a while so I though I'd do a little work on it this morning, here's a screenshot of where I've got to so far:

Here are the features Im thinking it will have:
  • 12-input pulse counter
  • Optional pull down resistor with option for SMT or through hole, see building blocks pages linked above for why pull down resistors are required.
  • Input status LED, driven by pulse signal.
  • Dedicated ATmega for pulse counting
  • Serial connection to second ATmega used for ethernet or/and rfm12 comms.
  • Enclosed in a DIN rail mounted enclosure.
Here's the eagle design so far:

I used the rfm12pi board design as a starting point as it already had the basic atmega + rfm12 circuit in place. 

One thing I'm still wondering about is whether to add a second optional resistor between the terminals and the pull down resistor which would provide the option of having a voltage divider on the input for stepping down from higher pulse voltages like 24V.

More to come soon..
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