Tag - Raspberry PI

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Friday, March 31 2017

Open Cycling Computer will be Pi Zero W based

Pi Zero W is the new brain of the Open Cycling Computer. PiTFT 2.8" capacitive dosn't work out-of-the-box, but required modification are very simple.

Modifications required in /boot/config.txt

1. Uncomment dtparam=spi=on

2. Add dtoverlay=pitft28-capacitive,rotate=90,speed=32000000,fps=20

Modifications required in /boot/cmdline.txt

1. Add after rootwait (the end of line) fbcon=map:10 fbcon=font:VGA8x8 logo.nologo

That's it! No other modifications are required.

P.S. 31-Mar-2017: Do not install adafruit kernel as it doesn't support bluetooth/wifi on Pi Zero W yet.

Sunday, February 8 2015

Bluetooth BLE, gatttool and (almost) all those numbers .... explained

It's a short guide to practical side of bluetooth LE using gatttool. How to read characteristics, turn on notifications and where to find more info about all those BLE numbers.

I was strugging for a while to read data from a BLE heart rate strap. It was working flawlessly with android apps, but I needed it to use it with raspberry pi and python. So, I had to dig a bit deeper under the surface of BLE. The results are below.

Prerequisites:

1. A computer with bluetooth v4.0 card or dongle

2. gatttool (part of bluez). Fedora users might have to compile bluez as there is no gatttool in bluez-5.23-1.fc21 bugreport: [1].

3. A BLE (bluetooth Low Energy, Bluetooth Smart) device - I use a Tacx heart rate belt [2]

An example command line session (red - important or info for later use, blue - value from previous steps, green - comment):

$ hciconfig
hci0:    Type: BR/EDR  Bus: USB
^^ hci0: that's our hci device
    BD Address: C4:85:08:06:9F:C7  ACL MTU: 310:10  SCO MTU: 64:8
    UP RUNNING PSCAN
    RX bytes:10243057 acl:34567 sco:0 events:5307 errors:0
    TX bytes:46612 acl:737 sco:0 commands:2685 errors:0

fedora-lan:/home/przemo
$ sudo hciconfig hci0 up
fedora-lan:/home/przemo
$ sudo hcitool -i hci0 lescan
LE Scan ...   <-- LE Scan was not showing anything, so Ctrl-C and hci0 reset
^Cfedora-lan:/home/przemo
$ sudo hciconfig hci0 reset
fedora-lan:/home/przemo
$ sudo hcitool -i hci0 lescan
LE Scan ...
D6:90:A8:08:F0:E4 Tacx HRB 04741
^^ D6:90:A8:08:F0:E4 that's BLE device address
D6:90:A8:08:F0:E4 (unknown)
D6:90:A8:08:F0:E4 Tacx HRB 04741
D6:90:A8:08:F0:E4 (unknown)

^Cfedora-lan:/home/przemo
$ sudo gatttool -i hci0 -b D6:90:A8:08:F0:E4 -t random -I
^^ if you can't connect try to use "-t random"
[D6:90:A8:08:F0:E4][LE]> connect
Attempting to connect to D6:90:A8:08:F0:E4
Connection successful

Reading velue of battery level characteristic
[D6:90:A8:08:F0:E4][LE]> primary
attr handle: 0x0001, end grp handle: 0x0007 uuid: 00001800-0000-1000-8000-00805f9b34fb
attr handle: 0x0008, end grp handle: 0x000b uuid: 00001801-0000-1000-8000-00805f9b34fb
attr handle: 0x000c, end grp handle: 0x0011 uuid: 0000180d-0000-1000-8000-00805f9b34fb
attr handle: 0x0012, end grp handle: 0x0015 uuid: 0000180f-0000-1000-8000-00805f9b34fb
^^^ 180f is "Battery Service", see link [3]
attr handle: 0x0016, end grp handle: 0xffff uuid: 0000180a-0000-1000-8000-00805f9b34fb
[D6:90:A8:08:F0:E4][LE]> characteristics 0x0012 0x0015
handle: 0x0013, char properties: 0x12, char value handle: 0x0014, uuid: 00002a19-0000-1000-8000-00805f9b34fb
^^ 2a19 is Battery Level, links [4] and [5]
char properties 0x12: supports NOTIFICATION 0x10 and READ 0x02 (0x10 | 0x02 = 0x12)

[D6:90:A8:08:F0:E4][LE]> char-read-hnd 0x0014
^^ Reading handle value
Characteristic value/descriptor: 64           
^^ value of battery level is 64, but it's hex, so 0x64 = 100. It's in %, link [4]
Reading heart rate
[D6:90:A8:08:F0:E4][LE]> primary
attr handle: 0x0001, end grp handle: 0x0007 uuid: 00001800-0000-1000-8000-00805f9b34fb
attr handle: 0x0008, end grp handle: 0x000b uuid: 00001801-0000-1000-8000-00805f9b34fb
attr handle: 0x000c, end grp handle: 0x0011 uuid: 0000180d-0000-1000-8000-00805f9b34fb
^^ 180d is "Heart Rate" service, link [3]
attr handle: 0x0012, end grp handle: 0x0015 uuid: 0000180f-0000-1000-8000-00805f9b34fb
attr handle: 0x0016, end grp handle: 0xffff uuid: 0000180a-0000-1000-8000-00805f9b34fb
[D6:90:A8:08:F0:E4][LE]> characteristics 0x000c 0x0011
handle: 0x000d, char properties: 0x10, char value handle: 0x000e, uuid: 00002a37-0000-1000-8000-00805f9b34fb
^^ 2a37 is Heart Rate characteristic, links [5] and [6]
char properties: 0x10: supports NOTIFICATION
handle: 0x0010, char properties: 0x02, char value handle: 0x0011, uuid: 00002a38-0000-1000-8000-00805f9b34fb
^^ 2a38 is Body Sensor Location, links [6] and [7]
char properties: 0x02: supports READ
[D6:90:A8:08:F0:E4][LE]> char-read-hnd 0x0011
^^ Reading Body Sensor Location
Characteristic value/descriptor: 01
^^ 0x01 it's "Chest", see link [7] for more options
We need more info to switch on NOTIFICATION of heart rate
[D6:90:A8:08:F0:E4][LE]> char-desc 0x000d 0x000f
^^ range of handles for heart rate: 0x000d is start of the range obtained with 'characteristics 0x000c 0x0011'
0x0010 is start of next characteristic minus 1: 0x0010 - 0x1 = 0x000f
handle: 0x000d, uuid: 00002803-0000-1000-8000-00805f9b34fb
handle: 0x000e, uuid: 00002a37-0000-1000-8000-00805f9b34fb
handle: 0x000f, uuid: 00002902-0000-1000-8000-00805f9b34fb
^^ 2902 it is Client Characteristic Configuration, link [8]
[D6:90:A8:08:F0:E4][LE]> char-write-cmd 0x000f 01
^^ 01 comes from link [8], NOTIFICATIONS enabled
Notification handle = 0x000e value: 00 3e        <-- heart rate, 0x003e is 63 BPM
Notification handle = 0x000e value: 00 3d        <-- heart rate, 0x003d is 62 BPM
Notification handle = 0x000e value: 00 3d        <-- heart rate, 0x003d is 62 BPM
Notification handle = 0x000e value: 00 3c        <-- heart rate, 0x003c is 61 BPM
[D6:90:A8:08:F0:E4][LE]> char-write-cmd 0x000f 00
^^ 00 comes from link [8], NOTIFICATIONS disabled
[D6:90:A8:08:F0:E4][LE]> disconnect              <-- end of connection
[D6:90:A8:08:F0:E4][LE]>
fedora-lan:/home/przemo/android

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1141909

[2] http://www.tacx.com/en/products/sensors/heart-rate-belt

[3] https://developer.bluetooth.org/gatt/services/Pages/ServicesHome.aspx

[4] https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.battery_level.xml

[5] https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicsHome.aspx

[6] https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.heart_rate_measurement.xml

[7] https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.body_sensor_location.xml

[8] https://developer.bluetooth.org/gatt/descriptors/Pages/DescriptorViewer.aspx?u=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml

Sunday, December 7 2014

Python library for Raspberry PI for Ultimate GPS based on MTK3339 with serial interface as sold by Adafruit

https://github.com/PrzemoF/mtk3339

Python library for Raspberry PI for Ultimate GPS based on MTK3339 with serial interface as sold by Adafruit. The library helps to set different chip parameters in a sane way. Currently supports minimum functional set of commands:

CMD_HOT_START - hot_start()

CMD_WARM_START - warm_start()

CMD_COLD_START - cold_start()

CMD_FULL_COLD_START - cold_reset()

SET_NMEA_UPDATERATE - set_nmea_update_rate()

SET_NMEA_BAUDRATE - set_baudrate()

API_SET_FIX_CTL - set_fix_update_rate()

API_SET_NMEA_OUTPUT - set_nmea_output()

SET_NAV_SPEED_TRESHOLD - set_nav_speed_threshold()

All functions are preforming basic range check to make sure values areaccepted by MTK3339 as there is no check if a call was successfull or not.

Example usage:

import mkt3339

gps = mt3339("/dev/ttyAMA0")

gps.set_fix_update_rate(800)

gps.set_nmea_update_rate(800)

gps.set_baudrate(115200)

gps.set_nmea_update_rate(1000)

gps.set_nav_speed_threshold(1.5)

gps.set_nmea_output(gll = 0, rmc = 1, vtg = 0, gga = 5, gsa = 5, gsv = 5)

That library is part of Open Cycling Computer project

Wednesday, October 15 2014

PiTFT capacitive calibration for vertical layout

PiTFT capacitive doesn't require calibration according to Adafruit, but for some reason I couldn't make it work properly with vertical layout and the default values suggsted here [1].

The default values are:

320 65536 0 -65536 0 15728640 65536

I needed to use the screen with Adafruit logo at the bottom [fbtft_device.rotate=90] and with the default /etc/pointercal values I had x axis swapped with y axis.

Explanation how the pointercal values works is here [2]. Some matrix math:

pointercal_equation.png

where:

x,y - the touchscreen coordinates returned by the kernel driver

a,b,c,d,e,f,s - pointercal values

u,v - the screen coordinates

The above equation converts to:

u = (x*a + y*b +1*c)/s

v = (x*d + y*e +1*f)/s

For the default values:

a = 320, b = 65536, c = 0 d = -65536, e = 0, f = 15728640, s = 65536

u = (x*320 + y*65536 + 0) / 65536

v = (x*(-65536) + y*0 + 15728640) / 65536

I wanted to flip x<->y, so

u = (x*(-65536) + y*0 + 15728640) / 65536

v = (x*320 + y*65536 + 0) / 65536

and now a = -65536, b = 0, c = 15728640 d = 320, e =65536 , f = 0,  s = 65536.

However when I tried to use those values in the pointercal file:

-65536 0 15728640 320 65536 0 65536

I found out that x axis is OK, but y axis is still flipped. To fix it we have to change sign of v and add a shift.

v = -(x*320 + y*65536 + 0) / 65536 +320

v = (x*(-320) + y*(-65536) +0)/65536 + 320

v= (x*(-320) + y*(-65536) +0)/65536 + 320*65536/65536

v= (x*(-320) + y*(-65536) +320*65536)/65536

v= (x*(-320) + y*(-65536) + 20971520)/65536

so d = -320, e = -65536 and f = 20971520

Proper pointercal values for vertical layout [fbtft_device.rotate=90] are:

-65536 0 15728640 -320 -65536 20971520 65536


Friday, August 22 2014

Bosch BMP183 with SPI by Adafruit in python on Raspberry PI

How to measure temperature and pressure with raspberry pi and BMP183

Requirements:

- raspberry Pi
- BMP183 with SPI by Adafruit
- 6 wire female-to-female cable or any other to connect 6 pins between RPI and BMP183

Results:

Temperature: 18.9 deg C

Pressure: 1013.39 hPa

RPI + BMP183: rpi_a_and_bmp183.jpg

Schematic (png): rasperry_pi_and_bmp183_sensor.png

That entry is the first part of Open Cycling Computer project

Schematic (QElectroTech): rasperry_pi_and_bmp183_sensor.qet

BMP183 at Adafruit

All files on github

BMP183 datasheet