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..
To engage in discussion regarding this post, please post on our Community Forum.