Discussion in "Project Help" started by    kakshay92    Jul 7, 2012.
Sat Jul 07 2012, 10:04 AM
I am trying to make the "Cellphone operated Land Rover" project given in the EFY magazine, pdf attached.

The H-Bridge IC circuit is working properly and to my knowledge, everything in the MT8870 DTMF Decoder IC circuit is also soldered correctly.

I am using Nokia 2300 for my project and the original earphones that came with it. They work properly when listening to radio, or talking to someone over the phone.

However, the MT8870 IC does not give output when I connect it to my AT89S52 microcontroller. I have written a simple program to transfer everything from port 0 to port 1 (in which an LED board is connected) - so that the corresponding output of the MT8870 (binary) will be shown on the LED board. But it continuously shows 0000, even on pressing keys.

The connector for my phone is of the TRRS type - and my speaker wires have connection to TIP and the second RING.

Please assist me in my project. I am unable to understand where I have gone wrong.
Sat Jul 07 2012, 08:15 PM
first u should get the dtmf o/p ....
in u r case check the crystal ,discreate components especialy capacitor.....
to see the tone is recive see the strobe pin on decoder ic ..when tone recive this pin is hi .....it means tone recived propely

''However, the MT8870 IC does not give output when I connect it to my AT89S52 microcontroller.''
means you get the o/p when micro is removed.....if this is problem see the ground connections of both are connected propely by a continouty test....
Sun Jul 08 2012, 07:19 AM
How do I check the crystal and capacitors?

I will try the strobe pin, thank you for that idea!
Sun Jul 08 2012, 06:15 PM

How do I check the crystal and capacitors?


If you don't have use of an oscilloscope the best way is to replace
the capacitors,then the crystal.

Check your soldering carefully.
Sun Jul 08 2012, 07:13 PM
@ kakshay92
attach circuit according to this schematic

i test it and it is working ok
first u has to be able to get out put of the decoder ic then go to controller that is second step
u can use this software to generate the DTMF tones in the pc or laptop
use headphone with the laptop and connect it with the circuit
now when laptop generate DTMF tones according to that led showw the status of the ic output
is is an easy and cost free method to check dtmf ic
i use this program is so useful
use stereo connector with laptop to IC connection
 kakshay92 like this.
Mon Jul 09 2012, 04:44 AM
I would be better if you check just the MT8870 receiver part first, remove your microcontroller and see the output of DTMF decoder using multimeter. this will ensure that a part of your circuit is working fine. then you can check controller side if things are going wrong.
Mon Jul 09 2012, 03:35 PM
Thank you everyone for your efforts! I went to my instructor and he suggested a few resistors and capacitor changes, am going to try that and hope it will work!
Mon Jul 09 2012, 05:56 PM
Good Luck kakshay92
 kakshay92 like this.

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Tue Oct 06 2015, 08:22 AM
HI you looking for ideas or you have solution
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poojitha: projects on wireless communication between two microcontrollers
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Have you searched our Embedded GSM Development and GSM and CDMA Discussion forums ?



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