Where do I get a POWER OK for Widget? from Tom Stepleton on 2018-03-28 (lisalist1)

From: Tom Stepleton <stepleton_at_email.domain.hidden>
Date: Wed, 28 Mar 2018 15:22:48 -0700 (PDT)

Hi everyone,

After probably two decades in storage, it may be time to try and resurrect an old, dead Widget I have in the closet. While I could try to tackle it with that NeoWidEx <https://github.com/stepleton/NeoWidEx> thing I wrote, I think this one's a bit too dead for that right now. Good thing I've got my very own UsbWidEx
<http://john.ccac.rwth-aachen.de:8000/patrick/UsbWidEx.htm> box, which I
completed just a few days ago. This should really help me figure out what's going on.

During my investigation, I'd like to power the Widget externally from a generic power supply---in fact, this one:

https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/0413645/

I'm curious what to do about Pin 3 of the power connector, though---the "POWER OK" pin according to this schematic
<https://computerarchive.org/files/computer/manufacturers/computers/Apple/schematic/Lisa/Lisa_Widget_Controller.pdf>.
Drawing from this old message about ProFile from Patrick Schaefer:

https://groups.google.com/d/msg/lisalist/yXkPP4_Yw88/WJNzHoBrUdwJ if the one for Widget is anything like the one in the ProFile, it's a sense line that tells the disk when the power is good. The recommendation there is to make your own POWER OK signal by using a Schmitt trigger to debounce the 5V supply line.

Meanwhile this old post on 68kmla just seems to recommend supplying 5V to the pin directly:

https://68kmla.org/forums/index.php?/topic/24905-widget-drive/&do=findComment&comment=261707 I'm not sure how smart that is, but it might work in a pinch?

And to be honest, I don't recall any bit of the Lisa 1.8A PSU providing a "POWER OK" sort of output. There are no 2/10 motherboard schematics online so far as I know, though, so I don't know if the signal might be coming from there.

Eventually my curiosity got the better of me and I decided to measure the real thing at the Widget power connector. On my 2/10 with a working Widget, I see the following:

With the Widget plugged in, there is 5V on the pin. Without the Widget plugged in, there is 0V on the pin.(?) All the voltages on the other pins are correct. This one puzzled me, so I measured it twice. 0V both times.

I have to say that I'm not sure how to make that add up. Anyway, the question stands: with regard to "POWER OK", what should I do to power a Widget on the bench?

Thanks for any help,
--Tom

-- 
-- 
-----
You received this message because you are a member of the LisaList group.
The group FAQ is at http://lowendmac.com/lists/lisa.html
To post to this group, send email to lisalist_at_email.domain.hidden
To leave this group, send email to lisalist+unsubscribe_at_email.domain.hidden
For more options, visit this group at http://groups.google.com/group/lisalist
--- 
You received this message because you are subscribed to the Google Groups "LisaList" group.
To unsubscribe from this group and stop receiving emails from it, send an email to lisalist+unsubscribe_at_googlegroups.com.
For more options, visit https://groups.google.com/d/optout.



text/html attachment: alternate version of message

Received on 2018-03-28 18:27:03