Electrical Modifications For Phidget 1012

  Sometimes last year, when I was about to order the remaining boards for input detection (for detectors & points status) I realized that the manufacturer of the board I was about to buy had a new product, capable of twice as many inputs. Namely - the new Phidget 1012 had 16 digital inputs as compared to the old Phidget 1018 board containing only 8. However there's a catch with the new board - it requires an external DC power supply.

  Even though I've previously believed that separate input boards are needed for optical detectors and for the switches' feedback, it turns out they can be handled by the same board. The key is using a ground level selected at the potential of 'brown' (of the Viessmann 5200 transformer). Going back to how the 1012 works - this will show an input as ON if the power supply has its circuit closed by the 1012's ground pin and that specific input (eg for input 0, this will be ON when the MRD1's relay is closed, namely when G and D1 are shorted on the figure below). Note that the DC power supply's polarity DOES matter. All in all, pretty straightforward for the optical detectors. Now for the feedback of switches, there's 'grey' and 'green' which get alternatively connected to the 'yellow' and 'pink' respectively, depending which way the switch is toggled. Since 'yellow' and 'pink' are actually outputs of the Phidget output board (1017), these are simply commanded by the input board's relays, which simply connect the "brown" of the Viesmann 5200 transformer to either 'yellow' or 'pink', respectively. So the key in getting the feedbacks to work with the 1012 as well is to have ground always connected to the same potential of "brown", which is made through a simple connection, as indicated in the picture below.

  Initially I had trouble understanding how this works, simply because both DC and AC notions apparently got together in the same figure. However the "brown" (BN) is a simple connection, there's no alternative current flowing through this diagram. It's simply that one can choose his arbitrary ground for the direct current.

  Special thanks go to John Parsons of Azatrax - the manufacturer of the optical detectors used on this layout - who was kind enough to point me in the right direction with the Phidget 1012.