PC Autodialout

Hi,

Most phones of either type will vary with the amount of rings before the voicemail service kicks in, usually followed by a long beep.

How to account for this time delay?

VoIP packages like SKYPE could maybe be used if they could be controlled throgh an application such as one writtn in Visual Studio ( or an Express Edition of C++ pr C# or even VB.Net ).

Regards,

Dr M.

I built a system over ten years ago that used a sound card and modem to call me on my mobile phone and verbally inform me that certain things had happened. The problem I had is the same one you refer to in that there is no way to know when the phone is either answered or diverted to voicemail.

One thing you can look for is a call time out where the telephone exchange automatically cancels a call after a certain number of rings. This will normally cause the modem to return an error code or a message like "call timeout" or "no answer" which can be used by an application.

One technique is to dial the number and continually announce something like "press # key to replay message" then wait for the appropriate tone to come from the mobile phone before playing the appropriate message.

I ended up just allowing sufficient time for somebody to normally answer a phone then playing any message several times to make sure that it was heard. If I ever got the message that the call had timed out I knew the call wasn't answered for some reason. I worked well enough and very few messages were ever lost.

As for what software to use this is a bit of a problem. Controlling com ports is usually a hassle with high level programs like Visual Basic and the application I use was a proprietary language specifically designed to drive com. ports. Unfortunately it required a special board to be installed in the PC and is no longer available so I can't help you greatly on this front.

MarshhallSoft Computing have a DLL (Dynamic Link Library) called WSC4VB (Windows standard Serial Communications For Visual Basic) that can drive serial com ports with subroutine calls from a Visual Basic program. It's a bit tricky to drive and isn't free but it dose give you the sort of control that you need, over a com port, from a Visual Basic program. You can download a trial version from the link above and see if it will suit your application before you fork out any money. If comes with some examples and the documentations is not that great. I used it to write a VB program that communicated with a GPS (Global Positioning System) receiver via a USB-RS232 adaptor and it took me about a day of playing around before I knew what I was doing so it's not impossible.

I hope that has helped and if you think I can help in any other way please fee free to contact me via the CR4 email service of by posting here.

First thought is that you would need to detect the telephone signalling tones such as dial tone (which I believe is 360 Hz + 450 Hz in the US) and the ringing signal (not sure about that one). If there is a human at the other end, he could be instructed to press # (for example) at the end of the message to terminate the call. You would then detect the DTMF code for "#". Also you could detect the recall signal which is a very LOUD series of beeps which is to remind you to hang up your phone.

All of the above is US related, so if you are elsewhere, you may have some very different protocalls.

Bill