For some reason, communications and power infrastructure fascinates me, especially the long-haul lines that move power and data over huge distances. There’s something about the scale of these projects that really gets to me, whether it’s a high-tension line marching across the countryside or a cell tower on some remote mountain peak. I recently wrote about infrastructure with a field guide that outlines some of the equipment you can spot on utility poles. But the poles and wires all have to end at the shore. Naturally we have to wonder about the history of the utilities you can’t see – the ones that run under the sea.
[dmalhar] was digging around in his bins for motors and found one with missing brushes. Being resourceful (and not able to find another motor), he managed to tear apart a SATA cable and form the pins into brushes with just the right amount of spring. Yes, this looks like a cheap motor, but in the moment of necessity availability wins, and this hack is truly commendable. If he had used a paperclip, MacGyver would have been proud, but the SATA cable pins make us proud.
Normally the brushes of DC motors are made with a graphite or some other material which provides a small amount of resistance so that when the motor is spinning the brushes will provide a gradual shift of current from one commutator to the next. Also, the softness of the carbon makes the brush wear down instead of the commutator, and in large motors the brushes are replaceable. In cheap motors the engineers design the brush material around the expected lifetime of the product. In [dmalhar’s] case, the motor just got its lifetime extended by a while.
A few weekends ago, [Chris] was in the mood for some retrogaming. That meant digging out the old Apple IIgs equipped with a monstrous RAM card with a whole three megabytes of RAM. This particular Apple IIgs had intermittent issues for a long time, and [Chris] was beginning to suspect the RAM was the culprit. Testing this required testing a few dozen individual RAM chips, so why not build something with an Arduino to make [Chris]’ life easier?
The chips found in [Chris]’ Apple are standard 1 M x 1 DRAM chips, the standard for late-80s computers. To test these chips on an Arduino, he picked up a beautiful ZIF socket, wired up the chip to an Arduino shield, and began the joyous process of figuring out how to interface DRAM to an Arduino.
Unlike static memories, DRAM needs to be refreshed periodically to recharge the capacitors. While this refresh cycle was the bane of designers and engineers throughout time, [Chris] actually doesn’t need to care about refreshing the DRAM. He’s just writing 1024 rows to the memory and reading it straight out – no need to refresh the memory. The trick comes from the multiplexed address bus. For his project, [Chris] needs to write 10 bits of the address, latch it, then write the other half of the address bits.
The DRAM tester was a success, and [Chris] put all the code and schematics up on GitHub. Solving the mystery of the broken Apple IIgs wasn’t as simple, as [Chris] thinks the problem might be in one of the support chips on the gigantic RAM card or the IIgs motherboard. Still, it’s a neat, quick build to test out a few DRAM chips.