ICL7611 op-amp (was: Motorola MC14081B)

Brent Hilpert hilpert at cs.ubc.ca
Sat Dec 24 13:04:13 CST 2016

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 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.

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:
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.

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