CC2540 connection problem

Hi Steve,

Do you use TI BLE MultiTool iOS App or do you have your own? If you could capture the communication with the TI Sniffer, It might be easier to identify the issue. Do you have an CC2540USB Dongle to use as a sniffer? Guide here.

I'll let someone more hardware oriented answer to the questions related to the PCB/antenna design.

Best Regards

Hi Steve,

Can you verify this with for example the TI BLE SensorTag app on the appstore?

Can you connect to the device using for example BTool or Device Monitor?

Best regards,
Aslak 

Hi Nick,

Thank you very much for your quick response. We are using the TI BLE MultiTool iOS APP. I will try to capture the communication with the TI Sniffer. Thanks for the tip!

BR,

Steve Chen

Hi Aslak,

We will first work with the sniffer using the TI USB dongle since that the only EVM kit we have. I will sniff the BLE connection status with BTool using the dongle as well. I will post my result later tonight. Thanks for your tips!

Hi Nick and Aslak,

I used both TI sniffer with TI USB dongle and BLE Multitool app with iPHONE4S.

When using the BLE Multitool app (version 2.1), I was able to connect to our custom BLE USB dongle with RSSI of -43dBM to -96dBM depending on distance.

However, when I used the TI Keyfob source code (V1.2.1) to build my custom iPhone app, I was not able to connect to our custom USB dongle with RSSI over -72dBM.

Moreover, when I sniff during the connection of my iPhone to our custom USB dongle, I see that there is error at FCS field. I've attached the log from BLE sniffer. Any suggestion on pointing to where the problem is will be greatly appreciated!

7367.ble-log-20130117-2030.psd

Hi Steve,

Can you clarify what you mean? Do you see worse performance with one iOS app compared with another?

FCS errors do occur from time to time for whatever RF reason. There is a bug when loading .psd files, so I can't see your RSSI values. However, you can see that for instance packet 4602 was correctly received by the iPhone (NESN=SN+1, i.e. the next SN is what the previous Next Expected SN was), even though the sniffer had an error receiving this.

Best regards,
Aslak 

Hi Aslak,

Not sure if its worse. But this is what I have done,

I've load two different TI app to my iphone

1) TI BLE Multitool app (I download from apple app store)

2) TI BLE Keyfob app (download from TI website)

Connecting to the same custom BLE USB dongle, I moved my phone to a distant about where the RSSI read back -76dBM (I got this number using the Multitool app). Then I try to connect to the USB dongle using two different app.

1) TI BLE Multitool app will show "connected" state in the Profile menu

2) Hitting the "Scan" key on the Keyfob app, it will change from scanning to connecting state, but it will remain in the connecting state despite my effort to move the phone closer to the dongle. However, if the phone was close to the dongle from the beginning I was able to see the "disconnect" state (I assume that device profile is properly received)

I just wanted to know that if this could be caused by hardware problem or it is more firmware/software oriented problem. The two different app, do they go thru the same connecting process?

BR,

Steve Chen

Hi Steve,

It may say connected, but can it discover services and characteristics? I.e. is it actually connected and able to do something useful?

It sounds impossible that two different apps actually have different RF performance, so I think it's just a difference in how they report the state.

Best regards,
Aslak 

Hi Aslak,

Using the Multitool, it was able to discover service and characteristics under the profile tab.

I feel the same way that its impossible for the app to change the RF performance. I will look into the code. But just out of curiosity, does TI release source code for the Multitool?

BR,

Steve Chen

Hi Steve,

We will release (and had released) a sensortag app example, which is similar to the Sensortag app and the Multitool app. However, it is temporarily down while we wrangle with the legal department about app distribution and license agreements.

Best regards,
Aslak 

Hi Chatto,

After spending some time to read and understand the application note AN098 and AN068, I have a question. What's the impedence needed on the differential pair of RF signal to the balanced port of the Murata Balun? The reason I ask this is that I have the change the stack height (to 1mm) of my pcb board due to mechanical constrains.

BR,

Steve

Hi Chatto,

Problemed solved! It turns out that I didnt solder the Balun well so that there are so interference with the RF. The custom boards I got back from the SMT factory worked well!! Thanks for everyone's help in this post!

BR,

Steve Chen

Hi,

where is the Pi RF network between the balun and antenna? 

Without that , the antenna and the wire to it may  not be Caliban to 50 ohm and you may have a TX/RX problem. 

-Nissim

When using a chip balun, the Pi or T filter/matching network is integrated into the chip balun. The unbalanced output impedance of the chip balun is 50 ohms.

However, it is good practice to have a shunt and series element at the antenna feed point to ensure that if there is some impedance mismatch at the antenna feed point, one can match using the passives.

Hi Nissim,

Thanks for the reply! I am no RF expert. But from the application note I read, it says that the Balun does not need a Pi network.

BR,

Steve