HDD activity LED's

[max1zzz]

Simple question, Where activity LED's in older macs on blinking off for activity or off blinking on (Like modern pc's)?

I need to sort out the activity LED circuit on my SCA to SCSI adapters (Which techknight pointed out to me was incorrect several years ago but I never got around to fixing...) and am trying to figure out which way to wire it but I don't have anything with both a original HDD and a activity indicator to check

 

[cheesestraws]

Simple question, Where activity LED's in older macs on blinking off for activity or off blinking on (Like modern pc's)?

I think off blinking on for internal hard discs (e.g. on the SE); on blinking off for external ones (e.g. HD20, 20SC), because in that case the activity light doubled as the power light.

 

[olePigeon]

@max1zzz @cheesestraws I'm fairly certain the LED is connected directly to the HDD on most models, so it would be dependent on the HDD manufacturer.  On many SCSI model HDDs, you can jumper the LED to On for Activity or Off for Activity.

By default with an OEM Apple drive, I'm pretty certain it's blink-on, even for the SE.

 

[mattsoft]

@max1zzz @cheesestraws I'm fairly certain the LED is connected directly to the HDD on most models, so it would be dependent on the HDD manufacturer.  On many SCSI model HDDs, you can jumper the LED to On for Activity or Off for Activity.

By default with an OEM Apple drive, I'm pretty certain it's blink-on, even for the SE.

This is the exact behavior on my SEs with OEM Apple drives for sure.

 

[cheesestraws]

By default with an OEM Apple drive, I'm pretty certain it's blink-on, even for the SE.

This is the exact behavior on my SEs with OEM Apple drives for sure.

Yup, that is what I meant; perhaps I worded it badly.  For clarity:

• On internal hard discs, such as the SE, SE/30, et al, with a separate hard disc light, the disc light is off most of the time and blinks on when activity happens.  This is the same as "PC" type behaviour.
  
• On external hard discs, such as the Apple HD20 and HD20SC (the external ones, not the internal 20SCs!), the power light and the disc activity light are combined, so the light is on most of the time and blinks off when activity happens.
  

In terms of wiring it; I'd default to "blink on" behaviour, and let people who want to have "blink off" behaviour provide their own inverter...

 

[max1zzz]

@cheesestraws@mattsoft@olePigeon Thanks

I'll build the next revision of board to be blink on for activity

 

[olePigeon]

@cheesestraws Oh, OK.  I read that as the opposite for some reason.  Nevermind, then.

 

[cheesestraws]

Oh, OK.  I read that as the opposite for some reason.  Nevermind, then.

I came back to that sentence this morning and had to read it twice to work out what I'd meant and whether I'd got it the right way around, so I think that was my fault!  Sorry to be confusing

 

[olePigeon]

This is somewhat related:  you can just use the interface board from an external 3.5" drive between the floppy connector and the drive to add a real floppy light to your Mac.  The only issue I've run into is securing that 3rd LED to the LED prism for the HDD/power LED.  I've thought about getting a bit of spare plastic and making a custom bit to clip on.

I tried using a single old red/green/yellow tri-color LED for all three, but the floppy LED is wired differently somehow.  It'd only work with the power + HDD, but I couldn't get the floppy LED to work in any combination on a tri-color.  I might revisit it.  Maybe I just need a diode or something inbetween the floppy and tri-color.