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Sim300C voice call problem

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Advanced Member level 1
Apr 19, 2006
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sim300c audio

I'm an engineering student and I'm using Sim300C for my university project.You can see the layout in this picutre.

Is this black plastic thing a MIC in the above picture?

1)I now write the AT commands on the computer(Hyper Terminal).

2)My phone starts to ring after a little while, I picked up the phone and speak on the phone and tries to listen my voice on the ear phone.

3)I can’t listen anything on the ear phone and neither in my telephone set.
3) Now I’m disconnecting the call

All the things are brand new, I am testing different commands on this sim300C module, I only have checked the SMS operation and it's working absolutely fine with no problem, then I wishes to make the voice call possible, I'm not able to do that and I'm currently stuck up in that.

Any kind of help would be highly appreciated from your expertise.
Umar Farooq,

sim300c headphone

try two rooms and a friend on the other phone
and speek into the 'black platic thing'
maybe there is a wire fault
ive picked up brand new headsets and sat scratching my head
till it dawns on me
im at a 'i bet myself its the ...' moment..duff cables etc

or a wrong connection

check it out and make sure the phone your using to rtx hasnt a setting to enable the headset mic or not

some people just use the headphone and actual phone as rtx and some phones do this
some networks wont allow two phones in a room and will shut down the audio of the calling phone to avoid feedback

gprs mic volume.. mic mute etc

audio on talk only setting within the software etc.... check this next
a i see its a module your using

hyperterminal maynot be setup right
better to ring a phone via the modem applet

this way the bindings are correct
hyperterminal wont allow transfer of audio

modem applet and direct dial will

you cannot bind audio via hypererminal i looked

you need to dial it from a controller app made for the module you have
or compatable gprs

basicaly you need to send more than the number to a phone


At this time of writing I'm in the university, I can't try out the TWO ROOM and TWO FRIEND experiement right now, I'll be back at my home today after some hours.

About Faulty Cable:
There is an AT command of CEXTHS, which when set detects the ear phone presence.When ever I insert earphone into the Sim300C evaluation kit, the Hyper terminal gives me the response about it's connectivity and whenever I remove the earphone it indicates me about it's disconnectivity.This proves that Cable is not faulty.

About Hyper Terminal:
Hyper Terminal is just used to send the AT command and that's it.It's not concerned with any audio application of the module.It has no concern where I'm sending this AT command, it's just being used to send the AT command on the computer serial port.This proves that Hyper Terminal is not creating problem.

About my Computer:
I don't have any MODEM install in my computer.I'm not using any features of my computer and nor any other card.My computer is being used to send the AT command on the Serial Port with the help of Hyper Terminal.

One question: have you try to call from your phone to the SIM300 modem? Is the same result that you don't hear your voice on this headset?

It made no difference which two methods I use:

1) Dial from Sim300C and recieve call on Phone.
2) Dial from Phone and recieve call on Sim300C.

But now my Problem Got Solved:
SIM300C is at the primary audio line by default.
This means that I had to connect a telephone handset to the handset
interface socket for voice communication, but I was using the earpiece(handsfree) for the voice communication.I then set AT+CHFA=1 for the earpiece configuration.Now I'm able to successfuly make the voice call.

Thanks for writing down your comments.Your suggestions really helped me to look and ponder at this problem from different viewpoints :)

Added after 5 minutes:

And yes, that "BLACK PLASTIC" thing is guaranteed a MIC :D

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