Saturday, April 17, 2010

How not to save I/O pins at the expense of safety: "There ain't no more up!"

Picture Kentucky Coal Miner on the phone, with thick Kentucky accent, to the maker of their Man-Hoist ("Coal Miner" for open air elevator, beats any Amusement Park ride, only next to the 'Man-Trips', the Roller-Coaster like ride that takes you into the Mine, where you may lose your head at any moment).
"Our Hoist only goes up. We've run out of cable, it is all on the spool. There ain't no more up!"

I'm sure you have experienced the frustration of needing just one more pin on your Micro. Here is why you don't let the Boss force you into take shortcuts to increase company profits today, only to be lost ten fold next month.

Seems the Hoist designers used two inputs one for Run/Stop and one for Up/Down. Up/Down faulted to 'Up', no mater what you wanted it to do, you only went up.

They should have used four inputs, Run,Stop,Up,Down. Up and Down together, or the absence of both would indicate a fault which could be dealt with before jamming up the machinery.

The morale of this design tip: Don't take short cuts, people ultimately pay the price. Warrant Repairs are expensive when you have to travel to the mine.