[hpsdr] Interfacing LP Filter for Pennywhistle

[Dick Faust]

I have a HF Projects LPF100 switchable LP filter that I plan to use with 
Pennywhistle until ALEX  is available.

There appears at least two methods to interface, but realistic 
documentation is lurking in a location that I have not yet discovered.

Approach 1 would be to use the Penny 25 pin connector J6  and connect 
"OC0 - OC6" [referred to in the manual as both "J6 Receive Pins" 1 - 7 
and "J6 Transmitt Pins" 1 -7] to the relays on the LFP100.  Seems 
straight forward except that I can not find on the schematic if pin 25 
"OCREF" is connected internally on the Penny board or if it must be 
connected on the LPF interface side - The ULN2003 would like this 
connected to the supply voltage.  My interest here is twofold and 
includes another application to interface to the THP  HL-45B as an 
FT-817 [decoded output].

Approach 2 is to use the 10 pin Mercury J6 "ALEX HDR 10P"  and duplicate 
the ALEX circuit for the SPI interface, which is quite easy.  What I can 
not find for this approach is the SPI message protocall, that would 
explain which outputs are used for what functions.  The Apollo schematic 
confuses the issue somewhat as it appears to use the outputs in a 
different selection than Alex [perhaps a different protocol].

Thanks

Dick Faust K9IVB