Author Topic: "Monitel" call timer/calculator  (Read 1133 times)

Offline gpo706

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"Monitel" call timer/calculator
« on: November 12, 2011, 01:52:59 AM »
Here's a Monitel unit, you sit your 700 series on the base, and as far as I can ascertain its self contained, not being directly connected to your POTS line just programmed with dialling rates.

It's GREEN and I have 2 greens to sit on it, a 706 and a 746.

Comes with instruction manual, BONUS!

Nice big fat LCD display on it.

Don't know if its gonna power up though!

Was there any similar bits of kit for the US market?
"now this should take five minutes, where's me screwdriver went now..?"

Offline Owain

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Re: "Monitel" call timer/calculator
« Reply #1 on: November 12, 2011, 12:10:45 PM »
do the instructions tell you how to punch the card for different rates, or was the user reliant on Monitel posting out a new card each time the rates changed?


Offline gpo706

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Re: "Monitel" call timer/calculator
« Reply #2 on: November 12, 2011, 02:28:53 PM »
Its not here as yet Owain, I have no idea if its card punched!

I bloody hope not!
"now this should take five minutes, where's me screwdriver went now..?"

Offline Owain

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Re: "Monitel" call timer/calculator
« Reply #3 on: November 12, 2011, 05:12:35 PM »
I think I can see the edge of the card (orange) poking out the top.

Good photo of the punched card here

Connected Earth

Offline gpo706

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Re: "Monitel" call timer/calculator
« Reply #4 on: November 13, 2011, 03:19:49 AM »
Thats amazing Owain, I had no idea it was punch-card operated.
"now this should take five minutes, where's me screwdriver went now..?"

Offline GG

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Re: "Monitel" call timer/calculator
« Reply #5 on: November 13, 2011, 06:54:20 AM »


What I'd like to know is, how was it connected to the phone?

I don't see any obvious way to wire it in.  So then: did it depend on the weight difference between on-hook and off-hook, plus an inductive pickup to detect dial pulses and the click when the line reversed polarity on answer...?  Or something else?   

I'm surprised GPO was apparently so sanguine about something that must have been customer-provided apparatus on its lines, and I've never seen a record of GPO providing that unit themselves. 

My preferred approach to metering is the use of high-frequency meter pulses and an odometer-like thing at the subscriber's station and at the exchange.   There would be two meters on the subscriber's unit: one that's resettable with an exposed pushbutton so you can time individual calls (and flatmates can do so for the calls they make); the other with its reset button concealed under a hinged flap so you'd press it to reset the unit at the beginning of each billing period.   This method also lends itself to simple customer-owned payphones that operate on the meter pulses just as the public phones do/did in some parts of Europe.  All of which can be entirely line-powered with no need for an AC mains transformer.

Though, IMHO, local calls should always be free and included in the monthly fixed rate for service. 


Offline Owain

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Re: "Monitel" call timer/calculator
« Reply #6 on: November 13, 2011, 07:49:40 AM »


What I'd like to know is, how was it connected to the phone?



It wasn't.

You pressed the button according to the charge rate of the call (L, A, B) and pressed the start/stop button when the called part answered, and pressed it again when you hung up.

It's probably based on a calculator-on-a-chip like the Mostek MK6010. To give an idea of cost in the 1970s, the first American-made pocket-sized calculator, the Bowmar 901B came out in the fall of 1971, with four functions and an eight-digit red LED display, for $240, By 1972 the four-function Sinclair Executive retailed for around $150 (79). The Mostek chip had 2,100 transistors in 360 gates plus 160 flip-flops.

If GPO706 will be good enough to post some piccies of the interior it will be interesting to compare the components and construction to contemporary pocket calculators from
Vintage Calculators

Offline gpo706

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Re: "Monitel" call timer/calculator
« Reply #7 on: November 13, 2011, 09:46:54 PM »
I will invest in a Nokia to USB lead folks, so I can get some pics for you.
"now this should take five minutes, where's me screwdriver went now..?"