DA14695-00HQDEVKT-RANG-ND not functioning correctly

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DA14695-00HQDEVKT-RANG-ND not functioning correctly



I ordered 2 weeks ago a Wireless ranging development kit DA14695-00HQDEVKT-RANG-ND from DIGIKEY ( 64453584 / PL1)

I started the basic test of connecting the 2 units to USB ports. 

The precision is far from the promised +- 0.5m. a distance of 30 cm ranges from 0.3m to 30cm, a distance of 1m is given as 3m. 

Also on 1 screen, the screen has rasterlines ( the resolution does not seem correct as the figures are twice as high. 

I have not undertaken any other step as I want to be shure that the products are OK



Last seen: 14 hours 26 min ago
Joined: 2018-02-08 11:03
Hi ghisbo,

Hi ghisbo,

Thanks for your question and for your interest in WiRa solution. In order to get accurate measurements, you should take care of the below :

1. Static measurement offset. The distance measurement is based on the phase difference between receiver/transmitter. The RF path itself can affect the measurement of the phase difference and present a static offset in the measurement. Our suggestion would be to set the CWD_STATIC_DISTANCE_OFFSET in the cw_distance.h file to zero ( 0 ). Put the devices at a measured distance points (e.g. 1m, 2m, 3m) and measure the distance with WiRa. If the devices are in line of sight with regards of the antenna radiation pattern and have the XTAL32M trimmed (see #2 below), then at all distances should present the same offset from the actual distance (+-0.5m). The difference found then is the static offset. Set this value in the cw_distance_offset global variable. Keep the of the CWD_STATIC_DISTANCE_OFFSET = 0;

2. XTAL32M trimming. It is important to have the XTAL32M trimmed at <=2ppm. If the XTAL32M is not trimmed in the devices performing ranging with WiRa, the distance and the static offset might be wrong. So, you can understand that the XTAL32M trimming is also critical for a well operational WiRa application. XTAL32M trimming is described in the Social Distancing Tag example documentation – please see section “ Crystal trimming”.

3. Generally, another factor that is important for the WiRa is the radiation pattern of the antenna. The WiRa relies to the fact that the devices are within each-other's antenna radiation direction. In case where the devices are not in the Antenna Radiation direction then the direct measurement might be too weak and not be possible to measure it. In such case a reflection to surrounding objects could appear as the "direct" reception, thus present as valid a longer distance than the actual as result of the ranging.

4. Avoid placing the ranging devices on a flat surface like a table or on the floor as the reflections of the signal on the surface will create heavy multipath with very small differences which will not be possible to filter. Have the devices at least 10cm from the flat surface to be able to measure correctly the direct path.

If the above steps are followed, then the Ranging becomes very reliable and accurate (within +-0.5m). Under no circumstances the WiRa is not designed for precise measurement of distance, but for accurate enough distancing of devices for applications where the 10cm is considered enough (like car key-FOB, Social Distance Tag, Smart-Locks, etc).

Thanks, PM_Dialog