05-21-2020, 05:19 AM
I am working on an enclosure for my SCP and one thing I want to do is have a means to easily connect an external drive. I have found the SCP makes for a nice way to test drives when repairing them.
Thinking of the various ways to do this the most straightforward would be to mount two IDC type, DB37 connectors on the case breaking the path of the cable to Drive1. A simple loop back cable would normally be in place to use Drive1 and when removed you could plug in the external drive. This is simple but takes up a bit of panel space for two large DB37 connectors. I suppose a small PCB holding two boxed male pin headers could be used instead of the DB37s.
Another option would be to just intercept the Drive1 select line and use a 74LS153 to toggle where it is routed, to internal or external drive. Looking at the SCP PCB (a picture only as I am at work) it looks like Huey and Lewy are buffering the signals to/from the bus so this would probably work OK. It would require a PCB, some 34pin headers, but only one external DB37. Thinking about it now two of the free pins on the DB37 could be used to sense when an external drive is connected so you would not need a select switch. is there any electrical downside to this I have not considered?
Thanks!
Thinking of the various ways to do this the most straightforward would be to mount two IDC type, DB37 connectors on the case breaking the path of the cable to Drive1. A simple loop back cable would normally be in place to use Drive1 and when removed you could plug in the external drive. This is simple but takes up a bit of panel space for two large DB37 connectors. I suppose a small PCB holding two boxed male pin headers could be used instead of the DB37s.
Another option would be to just intercept the Drive1 select line and use a 74LS153 to toggle where it is routed, to internal or external drive. Looking at the SCP PCB (a picture only as I am at work) it looks like Huey and Lewy are buffering the signals to/from the bus so this would probably work OK. It would require a PCB, some 34pin headers, but only one external DB37. Thinking about it now two of the free pins on the DB37 could be used to sense when an external drive is connected so you would not need a select switch. is there any electrical downside to this I have not considered?
Thanks!