The schematic can be found in the National Semiconductor AN-442.
All the boards can be mounted piggy-back. As this board will be normally used at the end of the cable, a 50R termination resistor are included with the jumper J67.
The DC-DC converter should be a 12V->9V, like the YCL DC-109. Also others can be used if the 7812 monolitic regulator U3 are changed acordly, like the 5V->9V YCL DC-101, but the regulator will get hotter.
The triple AUI type (1:1-1:1-1:1) ethernet transformer T1 can be bypassed if not needed with the solder jumpers that have below. The specified model are PE64104, but near any you could find in a dead 10base2 PC board will have one similar, like YCL 16PT-005, Delta THB16J15, etc.
The collision detection level can be modified to work with Transmit mode scheme with R61 and R62 and removing the weakened link between R62 and the isolated ground marked as JRXM, but for this application, a Receive mode scheme should be used to allow to detect remote collisions, so don't place R61, R62 nor cut the link.
The Collision detection signal output are in J64, but isn't used here. Place a 78R resistor there instead, to terminate the output.
R63 must be within 1% of 1K. There is provision to use some of the parts with smd package, so if you get the parts from an old board, probably could use all their parts.
The HeartBeat (or SQE) feature can be enabled with J66 removing the default trace link used for this application between pins 2-3.
U1 must be directly soldered to the board, due to termal restrictions. Also a small heatsink will be a good idea, since your board won't have plated holes to help to transfer the heat.
The board could be made single sided.
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