PP3 ,9V powered kit, 9V for brief power use and 3.3V via HT7133A-1 VR
for the uC. Simple 3 terminal device, In, out, gnd. Datasheet for the VR
says nothing about short circuit protection, in fact shows how to add a
discrete transistor for s/c protection. Normal use of this kit , for
manual switch off , not only the obvious isolation of the 9V but also
shorts across the 3.3V line to gnd.
The 9V lines are discrete gated in use , otherwise held off.
Requires something like 3.3R across the the VR output to make it drop
out, recoverably. The VR and micro resets itself and operates normally
after such a forced powerdown
This kit auto times out,via the uC, after 30 seconds of no use but I can
find no discrete item that crowbars across the Vdd line, to stop the
3.3V supply. Do they make uC (this one anonymous under black epoxy dome)
that can internally crowbar their own supply ? Just realised I've not
checked whether there is a 9V line to the micro, but still an internal
crowbar power option for a uC?