Attachment #1 shows the proposed wiring and CDS topology for the in air BHD setup. The PDF document has hyperlinks you can follow to the DCC entries. Main points:

1. I think we should run the realtime model on c1lsc. This will negate the need for any IPC between c1ioo and c1lsc machines.
2. I think we have most of the electronics we need already, though I am still in the process of testing the various boards, especially the HV ones.
3. We may choose to use the switchable whitening feature for the M2 ISS board
   • This would require some BIO channels
   • There are plenty spare in c1lsc, so it's not going to be a show stopper
   • This is why I've not explicitly included a whitening board for now...
4. The main job seems to be to make a whole bunch of custom cables. For the most part, I think we have the long (~20m) long D9 cables, so I propose just snipping off the connector at one end, and soldering on the appropriate connectors to the correct conductors.
5. For the homodyne phase control - the proposal is to use a PI PZT with 3 piezoelectric elements. We would drive the 3 elements with the same voltage, by shorting the conductors together (at least that's how I understood Koji's comment), so we'd only need a single DAC channel for this purpose.
   • Need to confirm that the parallel PZT capacitances (each element is ~300 nF so 3 in parallel would be ~900 nF) still allows sufficient actuation bandwidth.
   • If the relative actuation strength of the 3 elements needs to be individually tuned, we may have to use three DAC channels. The D980323 board will allow the driving of 3 independent channels. I have one of these boards in hand, but need to check if it works, and also implement the changes outlined here.
6. The alignment control has not yet been accounted for
   • We could consider using the in-vacuum PZTs, these were verified to be working ~2018.
   • If we use only 1 steering PZT mirror, we have sufficient free DAC channels available in c1lsc. But if we need both (to avoid clipping for example), then we need more DAC channels - we can either free up one DAFI channel, or install a DAC in the c1lsc expansion chassis. 
7. We may want to expand to have a second OMC at some point. In which case we'd need, at the very least
   • 1 more DAC card
   • A HV driver for the second OMC length (could use the Trek driver if we use D980323 for the homodyne phase control).

Please comment if I've overlooked something.