MCU

Project 1: Wireless data-acquisition

key words:

nRFL01

pic16F818

Picbasic Pro compiler

Python 2.5

references:

http://www.diyembedded.com

http://evertdekker.com/

http://www.microengineeringlabs.com/

description:

This projects describes a simple wireless data-acquisition module using the Nordic chip nRFL01 module from Olimex. The software code is based on the excellent tutorials listed in the references. For programming the micro controllers Picbasic Pro software was used from micro Engineering Labs. In order to visualize the measured data a Python program was written, thanks to the excellent examples available on the "net". Pictures of the set-up are shown below.

At one hand one has the PC interface module (pcb implementation) and on the other hand the sensor module (breadboard implementation).

The schematics of the interface module are shown below:

The PICBASIC code for the 16F818 MCU's are attached to this document. The Python code enables strip-chart monitoring of the data and post data-acquisition digital filtering. Thanks to the Python matplotlib module the graphics are excellent (cursor readout, panning & zooming, saving of the displayed graphics). The Python code is compiled to a "Windows exe - file" using Python py2exe enabling stand-alone applications.

Screen grabs of data-acquisition measurements using a 5 byte payload at 2 Mbps, ACK and shockburst mode are shown below. The maximum sampling period T-sample is limited to 7 msec mainly due to 5 msec time needed for the serial communication to the PC. When the data-acquisition is started (start measuring button pressed) the sample period (T_sample) and the number of samples (samples) are transmitted to the sensor module. When these settings are received, the sensor module starts the data-acquisition and sends the sampled data to the PC interface module. The incoming data is monitored by means of the strip-chart. When the data-acquisition is finished (text label: daq ended), one can press the history button which generates two graphs: the digital filtered measured data and the spectrum of the data combined with the filter characterisitic of the selected digital filter. Different filter characteristics can be selected by means of the filter radio button and the appropriate cut-off frequencies f_low and f_high. The text control "cal (ms):2" takes into account the 2 ms latency of the sensor module code execution.