24 Dec
2016
24 Dec
'16
7:04 p.m.
On 2016-Dec-24, at 4:07 AM, Adrian Graham wrote:
On 24/12/2016 03:48, "Brent Hilpert"
<hilpert at cs.ubc.ca> wrote:
The circuit makes sense if the battery is connected to the Vcc line of the ICL7611, 4081,
etc.,
D1 would be backflow prevention into the +12V line .
R416 would be current limiting providing ~ 8mA trickle charge of the NiCds.
Speaking of such equipment, our museum has one of these buried somewhere, a Nortel
Displayphone:
http://classiccmp.org/dunfield/disphone/index.htm
I don't think it has all the apps of the Executel,
it's phone + on-screen phone directory & phone apps + RS232 terminal with 300bps
modem.
I hope to work on it and document it sometime.
The ICL7611 is, I expect, a very-low-power
(Intersil's niche) op amp. Together
with the CMOS 4081 the circuit appears tailored for low-power operation.
Is it supplied by the battery?
It may require the battery presence for stable supply at time of power-up to
get reliable reset operation from this power-on-reset circuit.
That's a very good point so now I'm going to have to scrabble around to find
the battery to find out what voltage it was since I removed it ages ago and
may have recycled it. I don't recall any markings on it though, it looked
like a 'normal' 3 terminal NiCAD wrapped in blue plastic. I did take hi-res
pictures of it however.
The 5V input at R395 does head off towards the battery location before it
hits the resistor so I'll trace that out too.