Device Control using telephone(DTMF)

[vinodquilon]

That is a good idea.

But I use NE555, there is no specification about bypass capacitors in its data sheet.

 

[audioguru]

But I use NE555, there is no specification about bypass capacitors in its data sheet.

Philips assumes that you know that an ordinary 555 needs supply bypass capacitors. Did you look at the datasheet for the LM555 that is exactly the same IC?

Intersil mentions the 400mA supply current spike caused by an ordinary 555. Without proper supply bypassing then logic ICs that use the same power supply fail to work properly.

 

[vinodquilon]

dtmf

Philips assumes that you know that an ordinary 555 needs supply bypass capacitors. Did you look at the datasheet for the LM555 that is exactly the same IC?

Intersil mentions the 400mA supply current spike caused by an ordinary 555. Without proper supply bypassing then logic ICs that use the same power supply fail to work properly.

I think there is no need for separate relay for T point to Telephone line. We can connect T point to upper end of R18, thus comes in action only at off-hook time. But I think some sudden transients comes to IC7 due to sudden switching of RLY1 to ring volt. Pls give me a good solution.

 

[junxplus]

Sir,

Between two telephone lines how we can identify which line to be grounded and which one goes to DTMF IC.

You can test the telphone wire by using LEDs. LEDs will light up since they require little current. By the way, i am also doing the project. Can you please show me your progress and i hope yo ucan send me a clear schematic diagram?

 

[junxplus]

vinodquilon and audioguru, thank you for this thread. This will help me a lot in completing my project.

 

[vinodquilon]

You can test the telphone wire by using LEDs. LEDs will light up since they require little current. By the way, i am also doing the project. Can you please show me your progress and i hope yo ucan send me a clear schematic diagram?

Our progress is as follows,

On first step we have decided to check our MT8870 IC. See the link
IC dilemma- Please help on DTMF - All About Circuits Forum
As per the comment of AlexR we have decided to change the ring detection section with a 600Ω/600Ω isolation transformer. The reason is that, in our past circuit LEDs are ON on powering up the circuit. They doesn't change their state after ringing the phone. We think it is due to the failure in detecting the ring volt by the past circuits' input section. But now the problem is that, in our local market 600Ω/600Ω isolation transformer is not readily avail. So we are tempted to design and build our own transformer. Now we are in the designing of isolation transformer...

I cannot send you the full schematic as now we are only looking for the successful operation of DTMF IC. It is the core part of our project. If the IC testing is successful we can design our project in whatever manner as we desired.
Our resource links are, IEEEXplore_DTMF
dtmf Touch Tone remote device control (home automation)
Device Control Using Telephone: ElectroSofts.com
But the last two links contains lot of problems as pointed by audioguru in this forum.
Our aim is to complete the project without any micro controllers, only using discrete analog and digital components as it is only a mini project.

If you don't mind kindly share your valuable information. If you are successful in testing IC, kindly give the schematic....

 

[audioguru]

A 600/600 transformer is available in an old dial-up modem.

 

[junxplus]

ok. So i guess i will fail in completing the project in "Device Control Using Telephone" using the MT8870 and by following the old circuit diagram. I am going to go for the PIC16F84A to switch on devices since my project deadline will be on the third week of february. As soon as im done and with my graduation requirements, i am interested in helping you with your progress.

My problems faced right now is that I am using a 4N35 opto-isolator since the MCT2E aint available but what i have read from earlier post from audioguru the circuit diagram seems to have lots of errors.

I am giving you a reply of my progress in my next post and the link of the picture of the device iam making.