Here in the UK many service providers offer unlimited minutes for landline usage, but subject to a maximum call time of 60 minutes. My wife regularly overruns this when chatting to her best friend so I'd like some ideas on a timer circuit which will (ideally) disconnect the call after 60 seconds or, failing that, put a beep on the line so that she knows to hang up and re-dial. I've built a few circuits in the past but am still very much a newbie so unfortunately more abstract advice like "you need to build a self-oscillating feedback circuit" won't be of much use to me If anybody has built such a telephone timer circuit and would be willing to share, that would be ideal. As a side note, there is a ready built circuit board available fairly cheaply here in the UK but the timer only goes up to 20 minutes, so in principle I guess it is possible!
Many thanks,
Gary

 

I believe it is illegal to connect DIY equipment to the phone line in the UK.

 

I would imagine a simple digital count down timer could be set beside the telephone. At call start start the timer and get done before the timer has counted down an hour of elapsed time. This way it would not be invasive to the phone line.

Ron

 

Hi Ron, thanks for your reply. Yes that had occurred to me, however I was ideally looking for something that didn't require you to set a timer manually.

Regards
Gary

 

In the US, the proper way would be to use a DAA. See http://www.cermetek.com/catalog/telephone-line-interface/ I have no idea about UK requirements.

The PICAXE processor might be easy to use. www.picaxe.com

Your idea would nor be limited to one phone either. e.g.
Monitor the off hook time and inject a tone periodically starting at 58 minutes and auto-hangup at 59 minutes.
For incoming calls, you could say, make it beep 2x only and not hang up.

 

The current system generates revenue from phone calls be VERY careful how you present this idea on the webz.

 

@gary.
Here is one in a kit form upto 20 mins, it uses a CD4060 counter and Cd4093, easy to modify the timer, there is a circuit diagram on the download pdf..

http://www.jprelec.co.uk/store.asp/c=1693/Telephone-Cutoff-Timer-Kit-(1-20min)#

 

You can get a analog timer for a few dollars; just twist the knob and it will go bing when the time is up. It's not as annoying as having to set the time in a digital timer. http://www.ebay.com.au/itm/1-Hour-M...ountdown-Timer-Stop-Alarm-Clock-/252681477335

 

How about an electromechanical solutiom to the prohibition against connecting to the phone lines! Use a mechanical switch (or optical if you like) to detect when the handset is off the cradle.

 

The circuit will not work in some countries at the phone line gets reversed.

 

How about an electromechanical solutiom to the prohibition against connecting to the phone lines! Use a mechanical switch (or optical if you like) to detect when the handset is off the cradle.

And then a solenoid could press the cradle to disconnect the call after a suitable warning time.

 

The circuit does not disconnect the two parties. It merely "shorts the line."

 

Many thanks for all the replies. It seems that this isn't as straightforward as I initially thought so for now I'll just continue nagging her every time the phone bill comes in and maybe think about the more low tech solutions that have been suggested.