I am planning to purchase the EZ430-Chronos Devkit soon, but I wanted to clarify one point from the wiki. In the FAQs, it states:
"The 868-MHz and 915-MHz watch hardware are physically identical and the
radio frequency is software selectable so it's possible to switch
frequency if necessary. However, the RF Access Points for the two
respective kits are slightly different. The 868-MHz Access Point has a
0Ω resistor next to the antenna and the 915-MHz version does not. The
433-MHz kit is different than the other versions in both software and
Am I understanding correctly that the 868MHz and 915MHz Access Points are not frequency-switchable like the watches themselves are? If they are, does switching the frequency require additional hardware?
- Jeffery MacEachern
Thanks for the comprehensive reply. I was thinking something along the same lines regarding the "resistor" (albeit not as specifically). In this case, my motivations are much more simple: Digikey has no stock in the 915MHz model, and plenty of stock in the 868MHz model. If it was easily switchable, I wouldn't bother waiting to order. However, I don't really want to mess around with it; furthermore, according to the User's Manual, the USB dongle can only be reprogrammed with a (presumably) TI-specific device that costs as much as the devkit. I think I'll just wait.
IMHO there is no reason why the AP should use an antenna circuit that requires a hardware change while the watch uses a different one that doesn't.
Of course this is possible.Yet I think the resistor might be just a jumper that tells the firmware to configure the RF this or that way. While the software in the watch needs to be replaced for a different frequency.
Only a look into the schematics will tell :)
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I can confirm that the APs from both kits are physically the same save for the suspected 0 ohm resistor. I would have to assume the software on the AP is different as well, but do not know this for sure. If reprogrammability of the AP is required then a CCdebugger device is needed and some creative soldering will have to take place to get the new code onto the AP. The JTAG pins on the AP are brought out to some very small test point surface pads, but they are not in the footprint of any connector. If development of a custom AP is desired, the CC1111EMK would be recommended.
On the Chronos CC1111AP, the 0ohm resistor essentially "extends" the antenna length, essentially switching it from 915 to 868MHz.See the picture below, where the blue lines are the traces, and the red line is the 0ohm resistor that further extends the long trace to the short trace. This 0ohm resistor is present in the 868MHz version of the AP.
However, the CC1111 radio also requires different register configurations to operate at 868MHz // 915MHz, hence different firmwares are needed. If you have installed the Chronos SW package, you should notice 3 different firmware sets for the AP (433, 858, 915) located at C:\Program Files\Texas Instruments\eZ430-Chronos\Recovery\RF Access Point.
EDIT: 915MHz = no 0Ω resistor 868MHz = 0Ω resistor populated
Dung Dangthe 0ohm resistor essentially "extends" the antenna, essentially switching it from 868 to 915MHz.[...]This 0ohm resistor is missing in the 868MHz version of the AP.
But maybe this is extending the (estimated) 1/16 antenna at 868MHz to an 1/12 antenna at 915MHz, making it a little more sensitive.
If this is the intention, and if it works, it will compensate the range-loss at higher frequencies, making the 915MHz version reach as far as the 868MHz version.
sorry, typo, please see edited post. The extended antenna length is for the 868MHz, shorter one is for 915MHz. Nonetheless, the path-loss difference shouldn't be too significant when moving from 868MHz to 915MHz as these two bands are relatively close to each other.
To answer the the other question: to avoid complication and if you don't want to purchase the additional CC Debugger, you could wait for the 915MHz version to become available.
More information on the chip antennas (Johanson) of the two versions (from the datasheet, essentially replicated in the Chronos):
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