[tech] Coke machine lights, empty detection, fans

[Nick Bannon]

There've been a few Coke machine niggles:

 * the blinkenleds weren't visible - fixed
 * slot 0 and 5 neons were burnt out - fixed
 * slot 0 and 6 empty detection is broken - partly diagnosed

[TRS] and I put the blinkenleds back into place in the coin slot,
'till the next time someone pushes a coin through anyway. A couple of
wires had come off and were resoldered.

Slot 0 and 5 had dead 90V neons - now all the empty indicator lights work!
The neons aren't directly used for software empty detection anymore,
but it's nice to see them, especially when dispensing through the snack
machine panel.

There's 6 more spare neons inside the pocket inside the machine. Dunno
what their lifespan is meant to be, it might be normal or they might
get a little overdriven? Slot 0 has burnt out before, slot 5 may well
have been an original globe.

The neons all have a common rail; and they'll be turned on by 100VAC
(through current limiting resistors). The common side is about 60V away
from chassis ground and the switched side (when it's on) is about 40V
away from chassis ground. That 100VAC signal is cut down to size by a fat
capacitor/diode/resistor to drive an optocoupler, on the isolation boards.
The resistors get _hot_. The 4N38A opto on slot 0 is burnt out and gets
warm. Slot 6 empty detection sometimes works, possibly a dry joint.

The new empty detection system is sound in principle, but either it's
not perfectly in spec and eventually things can burn out, or we're
just unlucky.

On the other side of the optocoupler are the coke brain input lines -
slot 6 through to 0, 5V and GND. (grounded to the chassis of the whole
machine) If an input line is at 1.6V or more, or if it breaks or is
allowed to float (at about 1.9V), it's detected as not-empty. If it's
pulled low, 1.5V or less, it's empty (thanks [SGC] for the tests!).

The slot 0 and 6 input lines work fine, the slot 0 and 6 neons light up
fine, so it's definitely the isolation boards that are the problem. I
guess we should resolder the slot 6 joints and replace the slot 0 opto.
If it burns out again, we can try something different. ::-)

[MTL] and I inspected the fans recently - there were originally two
mains ones; and one broke. The 12V replacement works fine, so we should
probably go 12V-only and clean up some unnecessary mains wire.

Nick.

-- 
   Nick Bannon   | "I made this letter longer than usual because
nick-sig at rcpt.to | I lack the time to make it shorter." - Pascal