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Massachusetts Bodged Transistor Authority

in which two women are driven into madness by poorly documented cab signaling gear

A speedometer, with LEDs at certain specific points (0mph, 10mph, 18mph, 20mph, 25mph, 40mph, 50mph, 55mph, and 60mph) A big switch with “MAN” (presumably “Manual”) and “ATO” options (probably Automatic Train Operation as described) The serial number plate (not shown) indicates the manufacturer: “General Railway Signal”, who also made the ATO equipment on the Braintree branch! Inside, we found some wires with burn marks on the insulation, which we hoped weren’t connected to anything important (we would later figure out that they went to the incandescent bulbs and solder them back into place), and a delicate arrangement of LEDs on the speedometer dial. It's nominally rated for 50mV at 50mA, so we were a bit afraid to push it any farther, but after some experimentation we found that driving it using PWM from an Arduino pin (configured as an analog output) in series with a 360 ohm resistor worked fine.

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