Short circuit generator

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Pito
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Re: Short circuit generator

Post by Pito » Sat Aug 12, 2017 5:25 pm

If you short the probe's tip with gnd do you see 0V? If yes, then the measurements seem to be ok (talking here where you set the 0V on the screen).
There is none micro-controller in the phone. So the phone numbers are somehow hardwired on the pcb for the specific phone R1--Rx. Yes, there are the pin headers on the top you may set with an actual phone number.
The chips there are: 40103 - 8bit binary counter with presets inputs, which counts the pulses and compares with the number preset with the jumpers, and 4093 - 4x nand gates doing some timing (few RCs at its pins).
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Pito
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Re: Short circuit generator

Post by Pito » Sat Aug 12, 2017 5:56 pm

Your recorded dialing pulses - it seems to me your measurement is 400mV pulse 308us long on top of 10V.
So it pulses 10V->10.4V->10V on your picture..
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konczakp
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Re: Short circuit generator

Post by konczakp » Sat Aug 12, 2017 8:02 pm

Pito wrote:
Sat Aug 12, 2017 5:56 pm
Your recorded dialing pulses - it seems to me your measurement is 400mV pulse 308us long on top of 10V.
So it pulses 10V->10.4V->10V on your picture..
Then it would be very strange because logic analyzer would not show pulse for a 400mv change, I think. And Why the ringing signal would be made in a different manner than Receiver number signal ( 0v as Low signal )? This chip 40103 would recognize 400mV change ? But still, how can I pull the rail to low even if this would be only for ring signal ?

dannyf
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Re: Short circuit generator

Post by dannyf » Tue Aug 29, 2017 2:05 pm

.

To be able to communicate with other receivers. I think i need to do short circuit for a very short time (12us) to generate Low state on the power line.
That's a very odd way to communicate to anything. Before you proceed any further, I would strongly suggest that you confirm that's indeed the case.

With that said, using a mosfet, properly rated for this application, would be the simpkiest solution.

You may also check into relays, etc. As an alternative.

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ahull
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Re: Short circuit generator

Post by ahull » Tue Aug 29, 2017 3:56 pm

As I previously posted, breaking the line rather than shorting it, is the standard method of signalling on the majority of analogue telephone system I have ever worked on (and I've worked on quite a few). Shorting things out, with a dead short, even on a current loop system does sound a little odd, not to say a little dangerous, if high currents might be a possibility in the event of equipment failure.
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