https://github.com/danmar/mobilephone
mobile phone
https://github.com/danmar/mobilephone
Last synced: 10 months ago
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mobile phone
- Host: GitHub
- URL: https://github.com/danmar/mobilephone
- Owner: danmar
- Created: 2013-03-28T06:23:36.000Z (over 13 years ago)
- Default Branch: master
- Last Pushed: 2013-12-13T18:47:13.000Z (over 12 years ago)
- Last Synced: 2025-03-28T00:37:07.844Z (over 1 year ago)
- Language: C++
- Size: 7.62 MB
- Stars: 3
- Watchers: 2
- Forks: 3
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# mobilephone
Project to build a simple mobile phone (GSM). The mobile phone will handle
voice calls.
I will use off-the-shelf electronic components.
The software development and electronic components is sponsored by
Evidente.
## Progress
### Step 1 : GSM chip
I bought a SM5100B GSM chip, a simple evaluation board for this chip, and a
GSM antenna. The chip understands AT commands.
I bought a normal prepaid comviq sim card.
### Step 2 : Setup
I connected everything and tried to setup the chip for the GSM card. It was
quite straight forward.
By using AT commands from my PC I can send/receive SMS and dial/answer voice
calls (however I have no audio yet).
### Step 3 : Audio
The plan in this "step" is to connect a microphone and speaker. The datasheet
for SM5100B has reference designs for connecting microphone and speaker that
I will try to use.
According to the datasheet, the speaker can be connected directly to output
pins on the chip.
Before I had any parts, I wanted to "dry run" the audio. When a voice call is
made, it should be possible to measure something on the speaker output. I made
this connection:
GSM chip speaker output => voltage divider => microphone input on my PC
Oscilloscope view when I whizzle in the calling telephone
Audio recording when I say "test, test". It's very faint.
http://github.com/danmar/mobilephone/raw/master/images/3.wma
### Step 4 : Connecting the microcontroller to the GSM chip
Here I have connected a MBED microcontroller to the UART0 port on the GSM chip:
To start with the MBED just sends "AT" commands and then receive the response "OK".
### Step 5 : Prototype box
I bought a small box. The microphone and speaker I bought was connected. The
reference circuits from the datasheets worked fine!
Internal view:
External view:
The dialer is both used to dial numbers and to answer / hang up. By spinning the dialer
all the way twice you answer and hang up.
It works when using a AC/DC power adaptor. But unfortunately it doesn't work well from a
battery. I use a normal 9V battery right now. This may be too weak.