USB GSM Modem Interface with Hyperterminal/Embedded Controller

[Chen Jun Jie]

Hello everyone,

 

I am in need of some help, please allow me some of your time.

 

I have gotten myself a Huawei E1750 GSM USB Modem and a usb to serial RS232 adapter.

 

I will need to interface the rx and tx/gnd pin of my USB Modem – RS232 Adapter to the rx tx Pins of my LPC1769.
 

Problem 1) i am not able to send AT commands via hyper terminal as the modem has an USB interface, any alternatives to this ?

 

Problem 2)The modem requires a usb connection to achieve powered on status,  how can i achieve this without connecting directly to my laptop’s usb connection ? Is it possible to connect the USB modem to a self powered USB hub and connect the output of the Self-Powered Hub with the RS232 adapter to allow me to use the rx and  tx pins ?

 

 

Thank you for your time

 

 

[AJISH ALFRED]

 

1) Did you mean that you are not able to access usb port through hyperterminal?

     Well, there are softwares like MTTY, PUTTY etc. , through which you can send data to usb ports.

2) I’m not sure about power the modem using self powered usb hub, it will probably work.

    But RS232 is a serial to ttl converter and you need a different thing; usb to ttl converter !!

[Chen Jun Jie]

Hi Ajish, 

I have managed to send AT Commands via USB (PC to modem) now.

I was thinking, perhaps i could get myself a USB to Uart converter(FT232)  ? This way, i could make use of the existing USB GSM modem and interface it easily with LPC’s existing Uart pins.

 

Do you think the way i suggested will work with LPC 1769 ?

[Amrith]

 

Hi Chen,

 

Smart thinking. FT232 will help you to connect USB to your LPC17XX UART pins. This is the best solution.

[AJISH ALFRED]

 

Yes, it should work ! Please try the same and update.

[AJISH ALFRED]

 

And don’t forget to use a max232 (uart to ttl) between FT232 and the uart pins of the controller.

Its like,

                         usb<

---

>uart<

---

>ttl<

---

>mcu

[Chen Jun Jie]

Amrith

Thank You for the confirmation.

 

Ajish,
What you are suggesting is that the USB to Uart(ttl) outputs are not sufficient to drive communication between the USB modem and the LPC 1769 ?

 

I/O pins of the LPC 1769 are 3.3/5 volts tolerant, are you saying that the output volltage of the USb to Uart converter maybe too high and cause damage the MCU ?
 

 

 

Apologies, as i am new to this assignment.

[AJISH ALFRED]

 

I was actually worried about the communication standards, and not about the voltage tolerence!

 

I think you are talking about the kind of device found on the following link, right?

 

http://www.ftdichip.com/Products/ICs/FT232BM.htm

 

It is actually a USB to RS232 converter. USB is one communication standard and RS232 is another one. RS232 is the standard that we use in serial port (DB9 connector) of computers. Whenever we try to interface such a serial port with mcu, we use max232, don’t we?

max232 converts RS232 serial data standard to ttl serial data standard.

I hope it is clear now!

 

And that is the knowledge I have, if I’m wrong readers please share your thoughts.

 

 

[Chen Jun Jie]

Hi Aijish,

 

 

Is there a problem using FT232 ?

 

One of the PHD assistants told me that a USB Host/Slave issue might be present in my solution.

 

 

[Amrith]

Hi All,

I found some info on internet. Hope this may help you

Refer the link for data sheet: http://www.sparkfun.com/datasheets/IC/FT232R_v104.pdf

 

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[AJISH ALFRED]

 

Oh YES, he is right

 

USB is a master/slave or host/slave communication. Suppose you are connecting your GSM USB modem to the PC’s USB port. Here the PC is the host (and always will be) and the modem is the slave. Host initiate the communication by sending some data (requesting about hardware details) into the slave and the slave should reply to it properly before the actual communication begins. Thats how the host decide what kind of driver should be loaded to communicate with that particular slave.

 

In all USB devices that is meant to be communicated with a PC have a hardware inside it called SIE (Serial Interface Engine). It manages all the communication between PC and the USB device. So in order to communicate with such a USB device you should have drivers written for it.

 

In your case your simple microcontroller should act like a master and the modem as slave. So you can connect the modem only if you can code for a driver in your mcu

 

It is like,

                                                                                       |

                      GSM USB                                                 |

                       modem     <— connecting circuits

---

>  |  USB driver

                        (slave)                                                     |    code

                                                                                        |

                                                                                        |        MCU

                                                                                        |

 

For more details about USB host/slave communication find this useful link

http://www.maxim-ic.com/app-notes/index.mvp/id/3803

 

[Chen Jun Jie]

This was the data sheet that gave me the idea.

 

Renewed confidence, thanks Amrith !

 

[Chen Jun Jie]

edit – I saw the post. 

 

Hmm, this is interesting.

[AJISH ALFRED]

 

Chen,

 

I’m sorry, but it just won’t work out that easily! Your PHD friend is right.

 

[Anonymous]

i want some help on your engineesgarage wedsite so i hope you clarify our doubts

[Author]

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