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The ULN2001A, ULN2002A, ULN2003A, ULN2004A, ULQ2003A, and ULQ2004A are high-voltage, high-current Darlington transistor arrays. Each consists of seven npn Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collector-current rating of a single Darlington pair is 500 mA. The Darlington pairs can be paralleled for higher current capability. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers
That's close but I think the term came from line printers like the IBM 1403. The hammers were solenoids that came out and struck the paper from behind pushing it into the characters on a chain as they went by the location on the page where they were to be printed.
At Princeton University (ca. 1962-64) there was a guy who made a card deck that when sent to the printer would play "She'll be coming 'round the mountain" from the sound of the hammers hitting the paper. Somebody clearly had way to much time on their hands.
In the early dot matrix printers like the Centronics 101 they were called pin drivers and they were similar but operated at lower voltage and current. There was so much mass on the head for seven solenoids that those printers could actually walk themselves off the table.
It's hard to imagine that there was a time before your time 3VO, but there was. Grin
I've got hundreds of them from three old, very large (400-500 lbs) IBM printers. Posted some pictures a while back for Hank Fletcher's robot-recorder project. They look more like relays (without contacts) then anything else. Haven't found a use for them.
Speaking of line printer hammer drivers, I still sometimes have nightmares about the hammer driver alignment adjustments I had to perform at times as a field service engineer on mini-computer systems.
The large drum line printer had 132 column hammers that would strike the spinning engraved print drum when the proper characters would line up with the proper column. The alignment procedures had one print the same character for all 132 print positions and one would have channel one of a O-scope set to see the counter EMF pulse for hammer #1 and the channel two scope probe would be moved to hammer numbers 2 through 132 one at a time and adjust a mechanical set screw so that the adjusted hammer so it would match the #1 hammer pulse. This was a very time consuming procedures and the sound that the printer would make while firing all 132 hammers at the same time so tremendous, lights would dim in the room. If this procedures wasn't done every six months or so the print lines would start to appear 'wavy'.
At the time, in to 70s, that model printer cost as much as the home I was living in!
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