L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 8

The systems design for the SFENA HSI integration calls for a number of discrete I/O pins to be handled via a National Instruments DAQ card. The card that I use for this setup is an older PCI-DIO-96 card. The TTL level I/O on the card controls a set of relays supplying 24VDC to the discrete pins on the SFENA HSI.

HSI Integration of 24V Discrete Channels

The video at the top of the blog posting shows the operation of the relays via the NI card. The SFENA HSI supports the following discrete inputs:

SFENA HSI Discrete Input

The instrument specification actually asks for a range between 18.5VDC and 28VDC as the "hi" value for the pin, therefore, the 24VDC source that I use is well within the design limits.