This update applies to a project posted here on 2-15-2009.
As originally designed, the PC's fans would be powered up along with the second hard drive which is used infrequently for data back-ups. Normally the PC is a silent fanless system with the primary HDD housed in an aluminum enclosure which serves as a heatsink and noise suppressor.
Occasionally, under high CPU loads, the fans are needed to circulate air for the fanless CPU heatsink when the PC is in operation and the second HDD has been latched off.
After applying the simple modification shown in the attached image, the external switch now serves a dual purpose. As before, the switch controls the initialized state of the second HDD as selected before booting up. Now, the switch also controls 12-volt power directly to the fans at any time, independent of the state ot the latched relay.
HDD Latch Update for Manual Fan Control
This update applies to a project posted [URL="http://www.electro-tech-online.com/electronic-project