This is possibly about the most difficult part of the whole signalling project !
Four gates. To safely run trains, all four gates must be securely in the "open" position. Each gate is required to comply with the 'Moving Part Rule' - reporting the two bit binary code for "open" to the signalling system. Any one or more gate failing to report "open" will be sufficient to set all nearby signals to "Danger".
Gates are to be operated from the signalling system, which will energise whatever actuators are used - all simple enough, no probs.
The problems arise in agreeing how the gates are used.
Manual operation must be allowed when signalling not in use. Conversely, manual operation should not be allowed when signalling is in use.
How do we prevent gate being swung into path of approaching train?
Let's talk this through soon, then get some progress on the ground!