IR sensors
- count how many cars go past
  - compare to record of train, make sure no cars have been lost
- must be able to sense space between cars reliably
- determine when appropriate coupler is over decoupling magnets


RFID (NFC) sensors
- confirm record of which cars should be attached to each loco


Bump sensors
- placed in each loco to sense when it backs into cars


Speedometers
- a pair of sensors used to check speed of train
- results used to create table of speed of each loco with given load


Section sensors
- identifies when a section is occupied
- if using IR, set at intersection of every track section
- calculate speed of train through each section with current load
  - results can be used to create a table of expected travel times


Sections
- each section should have a max speed


Motion sensor in each loco so it knows if it has stalled?

Cars attached to loco
- Resistance (needs a resistor in one wheel of each car)
- wire length measurement
- capacitance
  https://www.arduino.cc/en/Tutorial/CapacitanceMeter


----------------------------------------


Table for location sensors:
Sensors		Section
1:2		AA
2:3		AB
3:4		AC
1:4		AD
1:5		BA
5:6		BB
1:7		CA
7:8		CB
1:9		DA
9:10		DB


0 = block clear
1 = block warning
2 = block occupied

Keep one table that shows only occupied/clear status
- when loco triggers sensor:
  - add sensor to train's list of locations
  - mark block between this and next sensor as occupied
- When sensor clears:
  - mark previous block as clear
  - remove previous sensor from train's list of locations
  - If only 1 entry for locations and blocks, keep them marked
    until train trips the next sensor (prevent train from
    disappearing when it is between sensors)


location: A<B:C>D
- A   = previous sensor that has cleared
- B:C = sensors currently tripped
- D   = destination, next expected sensor

Train going clockwise around loop:
location 1<>4, block <AD>AC
location 1<4>3, block <AD:AC>AB
location 4<>3, block <AC>AB
location 4<3>2, block <AC:AB>AA
location 3<>2, block <AB>AA
location 3<2>1, block <AB:AA>AD
location 2<>1, block <AA>AD
location 2<1>4, block <AA:AD>
location 1<>4, block <AD>

*trigger: "1<" means train has passed sensor 1
Reverse train direction, reverse order of location and block

Train wants to back into siding 9:10:
location 4<>1, block <AD>DA
location 4<1>9, block <AD:DA>DB
location 4<9:1>10, block <AD:DA:DB>
location 1<9>10, block <DB:DA>
location 9<>10, block <DB>
location 9<10>, block <DB>

*trigger: "<10>" stop train.

If train trips an unexpected sensor, stop and sound alarm.


Create new table that also shows warning status
  loop through all blocks {
    if block occupied {
      check blocks on either side {
        if (block == clear) mark block = warning
      }
    }
  }
This table is used by locos and signals

- Trains are designated as a blob of occupied blocks so they can
  move in both directions and still maintain a solid area.
- Keep a table of each train with unique designation
  - include all locos and cars
  - include location blob


Routes:
Train is sitting in CB, must pick up car from DB, go around loop,
  drop car at DB, park in CB.

CA:AD:1<=R (reverse direction after clearing sensor 1)
DA:DB:<10>=R (reverse direction when sensor 10 is triggered)
DA:AD:AC:AB:AA:AD1<=R (reverse direction after clearing sensor 1)
DA:DB:9<=R (reverse direction after clearing sensor 9)
DA:AD:1<=R (reverse direction after clearing sensor 1)
CA:CB:<8>=S (stop after triggering sensor 8)


BadRoutes:
Dest	Bad
AA	CA:DA
AD	BA
DA	AA:CA
CA	AA:DA
BA	AD

Turnouts:
Route	Turnout(s)
AA:AD	t1=0:t2=0:t3=0
AA:BA	t3=0:t2=0:t1=1
AD:AA	t1=0:t2=0:t3=0
AD:CA	t1=0:t2=0:t3=1
AD:DA	t1=0:t2=1
BA:AA	t1=1:t2=0:t3=0
BA:CA	t1=1:t2=0:t3=1
BA:DA	t1=1:t2=1
CA:AD	t3=1:t2=0:t1=0
CA:BA	t3=1:t2=0:t1=1
DA:AD	t2=1:t1=0
DA:BA	t2=1:t1=1