OK, folks. I admit to not considering that the TS only had a limited parts selection. It was an option I suggested to reduce the cost, because transistors with a slightly higher voltage rating are often cheaper than those with a considerably higher current rating. So the four bulbs could also be operated in parallel, and the switching transistors will need higher current ratings. Not a huge problem.

 

BTW, the schematic in post #4 is just one option for how to assign the lamps to driver outputs. There are many others. Here is one that minimizes cross-wiring. The light-bulb-to-driver-pin assignments are different, but there still is one bulb per driver.

The ULN200x / 280x drivers have a maximum ground pin current spec. IIRC it is 1.5 A. So while each driver section is rated for 0.5 A, you cannot have all 8 drivers in one package sinking that much current simultaneously (4.0 A). With this schematic version, the max GND pin current is 0.84 A, only 56% of the GND pin rating.

ak