a blog about computers and other funny things
Month: November 2018
This is a nice way to write with joysticks:
Unfortunately this idea is patented: U.S. Patent #7,729,542
http://depts.washington.edu/ewrite/
I think this patent is supposed to expire in 2027!
It should be nice if patents last for 10 years or less, it could help to make innovation more accessible for everybody.
I just created a driver for NuttX to use JLX1602G-390 display.
This display is based on Siatronix ST7032i the I2C version.
First you need to wire it connecting an external capacitor and a resistor as explained on this schematic:
I am using the STM32F4Discovery board with this display connecting pins PB6 to SCL and PB9 to SDA. These pins are configured to enable an internal pull-up resistor, but case your microcontroller doesn’t have it, you need to connect external pull-up 4k7 resistors to SCL and SDA pins.
After configuring the NuttX to use this display, you can execute the slcd command from NuttShell:
nsh> slcd Opening /dev/disp0 for read/write access Attributes: rows: 2 columns: 16 nbars: 0 max contrast: 0 max brightness: 1 Clear screen WRITING: 0000: 1b5b46 .[F Set brightness to 1 Print [Hello World NuttX] WRITING: 0000: 48656c6c6f20576f726c64204e757474 58 Hello World Nutt X Test complete nsh>
You can see the step-by-step video tutorial here:
Source of this schematic: https://bitbucket.org/ospringauf/mecanumrover/wiki/JLX1602G-390
After implementing the MLX90614 driver for NuttX I noticed that although the write command to change the device I2C address in the EEPROM was reporting success, after the power cycle the new address was not working. Worst: even the previous address was not working.
Basically the device appears damaged and didn’t respond to any I2C command.
Then doing my research I discovered a Melexis document about SMBus communication:
Click to access MLX90614_SMBus.pdf
In this document I noticed they are using the address 0x00 instead of the default 0x5a address. After modifying the driver to use the 0x00 address the device accepted the new command.
There are many discussing about this subject on Arduino and similar forum:
https://chrisramsay.co.uk/posts/2014/09/arduino-and-multiple-mlx90614-sensors/
http://forum.arduino.cc/index.php?topic=54170.msg539601#msg539601
https://forum.mikroe.com/viewtopic.php?f=178&t=67842
http://wiki.wiring.co/wiki/Connecting_Infrared_Thermometer_MLX90614_to_Wiring
Note that someone discovered that using a brute force CRC approach eventually will work and everybody decided to copy it. Too bad guys!
The MLX90614 uses CRC8-CCITT standard to check if data are correct, so any CRC8-CCITT implementation will work, for example this one: https://3dbrew.org/wiki/CRC-8-CCITT
Now on NuttX you can call the mlx90614 example application to change the device’s I2C address this way: (changing from default 0x5a to 0x3a)
nsh> mlx90614 0x3a Address 0x3a stored on your device! Please do a power cycle and update the I2C board address! nsh>
Alan C. Assis 