AVR GCC LCD library allows connecting pins in any order

Posted on December 17, 2011 | Leave a comment

Probably some of you are struggling in finding a proper LCD driver that would work on any circuit. Just wanted to point out that I found some time to improve my current LCD library so it would support a mixed pin connection case. Earlier you had to connect LCD in pretty strict way where pins had to be aligned and connected to single AVR port. Sometimes this can’t be done due to various reasons – you want to use those pins for other alternative functions or simply you want to trace your PCB better etc.

In this updated version of library there are two more modes added : LCD_4BIT_M and LCD_8BIT_M that allow controlling LCDs either in 4 or 8 bit mode but with any pin connection layout. So data pins and control pins can be connected to any pin number and any port. Couple examples should give some clue on how to start using it. If you used this library for some project you only need to modify header file while project source code can remain same. Download LCD library here.

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Modeling of analog part for DDS3 signal generator

Posted on December 12, 2011 | 3 Comments

When building AVR DDS2 signal generator there were lots of discussions about signal conditioning in analog part of device. First argument was that LM358 wasn’t the best choice for this purpose. Another one pointed to sine wave that weren’t smooth enough.

As you can see there are some dents on it. Other waveforms also are distorted especially when higher voltages are selected. This definitely asks for better analog part. Some people suggested to replace LM358 with OPA2134, but it seems to be quite expensive choice. In my opinion low noise general purpose op-amp can be great too. I’m gonna give a try to Texas Instruments TL074 low noise op-amp. It is low power, high slew rate (13V/us) IC – almost five times faster than LM358 and for same reasonable price. Continue reading →

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Posted in AVR controlled signal generator, Electronics

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FreeRTOS on STM32

Posted on December 5, 2011 | Leave a comment

High density line of STM32 microcontrollers have quite a bunch on features that can be used in user programs. The more features you add to source the more complicated program becomes and this way it starts to be difficult to keep up with all things. Using only main loop and interrupts becomes time consuming task to manage. If you don’t want to struggle in tuning things up manually you can use one of many real time operating systems (RTOS). They are great when you need lots of separate functions to run in parallel so no task would be missed. RTOS scheduler takes care of giving each task a decent time to perform. There are lots of great RTOS systems around. Many of them are free and opensource.

It happens so that I love using FreeRTOS which has quite long history and is flexible enough to fit multiple types of hardware. You can check out my recent demo on Atmega128. I encourage you to give a try to other RTOS systems like ChibiOS, BeRTOS, and many more. But lets stick with FreeRTOS. Simply speaking FreeRTOS is quite simple and easy to use. It has practically most of features you’d look for in RTOS. Some of key features would include preemptive, cooperative and hybrid scheduler, task and co-routine support, queues, semaphores and mutexes for task synchronisation and communication. Many demos, many ports to to get started with. Continue reading →

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Posted in ARM microcontrollers, Projects, STM32

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Driving Graphical LCD with STM32F103ZET6

Posted on November 19, 2011 | 2 Comments

STM32F103ZET6 board comes with 3.2 inch graphical LCD which features an ILI9320 controller. Equipped LCD is capable of displaying 252144 colors when driven in 18-bit mode. We are gonna drive it in 16-bit mode, so we are limiting it to 65K colors.

LCD driver is based on existing code found on internet which was originally developed for STM3210E board. Only minor modifications were needed like assigning right control pins. Continue reading →

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Posted in ARM microcontrollers, Projects, STM32

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Connecting STM32 USART to standard I/O streams in GCC

Posted on November 18, 2011 | Leave a comment

In many situations when working with STM32 microcontrollers you will want to output text strings. There is no need to write special functions that output specially formatted strings as it is hard to keep up with various cases. Simply speaking it is convenient to use standard I/O streams and its library functions that allows sending formatted data streams.

Arm GCC toolchain comes with newlib C library from Redhat and so it isn’t specially designed for embedded toolcain. In order to use stdio functions we have to take care of several syscals so called “stub functions”. These functions normally are provided by operating systems like you would write C programs in Windows or Linux. In our case we aren’t using any OS, os in order to avoid error messages while compiling we have to provide these function declarations where most of them are dummy implementations. It’s not something new pick one that you find on internet. I found on that was written for STM32 Discovery. Continue reading →

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Interrupt based button read on STM32F103ZET6 board

Posted on November 14, 2011 | Leave a comment

In previous example we implemented a simple demo program that reads buttons by constantly checking their status in main program loop. Obviously this isn’t efficient and convenient way to do that. Imagine your program has to do lots of tasks and in between you also need to check button status – mission becomes impossible unless you use interrupts. In this part we briefly introduce to STM32F10x interrupt system and write example code where LEDs and buttons are serviced within interrupts.

ARM Cortex-M3 microcontrollers have advanced interrupt system that is pretty easy manageable. All interrupts are controlled inside Nested Vectored Interrupt Controller (NVIC) which is close to Cortex core to ensure low latency and robust performance. Main features of NVIC include: Continue reading →

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Implementing buttons on STM32F103ZET6

Posted on November 7, 2011 | Leave a comment

Last time we have made a good starting point with setting up a project template for STM32F103ZET6 development board using GNU tools. Using same project template we can move forward and start programing other elements. This time a quick note about adding button library. This is really modest implementation which simply initializes port pins and then reads their status.

Development board is equipped with four user programmable buttons named WAKEUP, TAMPER, USER1 and USER2. We are not going to care about meaning of names just use them as general purpose buttons for now. Continue reading →

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Driving LEDs with LPC2148 microcontroller

Posted on November 5, 2011 | Leave a comment

Couple years ago I have purchased LPC2148 development board called BlueBoard form ngxtexhnologes. It is quite powerful board with ATM7TDMI series microcontroller which is considered an old guy comparing to Cortex ones. But still these are widely used and are powerful.

Development board has some handy features installed. 12MHz crustal allowing to run processor at full 60Mhz speed. Couple RS232 ports, VGA connector, PS/2 connector for keyboard or mouse, 20-pin JTAG, SD/MMC slot, USB B-type, 8 LEDs driven with serial-in parallel-out shift register, 2×16 LCD, buzzer, audio jack with amplifier, two programmable buttons and 256Kb of I2C interfaced EEPROM. Microcontroller itself has 512KB of internal flash and 32+8KB of RAM. All ports are accessible and any external hardware can be disconnected with jumpers. This is great board for prototyping and end application. Continue reading →

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LED blinky demo on STM32F103ZET6 development board

Posted on November 4, 2011 | Leave a comment

Found some time to play with STM32F103ZET6 development board and decided to set up a simple project for it. Probably the trickiest part of this is to set up a project environment that would serve as template for following developments. Obviously we choose GCC development tools. Many ARM developers chose CodeSourcery Lite edition toolchain. It has full command line functionality – this is what we usually need. If you want some alternative – you can choose Yagarto GNU ARM toolchain which is also great and free.

No matter which tool you select code will work on both. Lets stick to CodeSourcery. Just download it and install to your PC. As we said Lite version supports only command line tools – we need an interface for it. Eclipse IDE is one of favorite choices, so we will grab this one too. Yagarto website has a nice tutorial on how to setup Eclipse IDE in step-by-step manner. We wont go in to details with this. Continue reading →

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FreeRTOS on AVR with external RAM

Posted on August 31, 2011 | 1 Comment

AVR microcontrollers aren’t best choice to run FreeRTOS scheduler due to low RAM. Atmega128 has only 4K of RAM memory, so this limits FreeRTOS functionality to very basic. Anyway this can be solved by adding extra RAM connected to external memory interface. We have already implemented external memory block of 8K previously so now we can muck around.

Lets continue with our previous code having several simple tasks (button state reading, LCD output and LED flash), and add more to it. We are going to set up external RAM for storing heaps. This will allow to store large data buffers without worrying of heap and stack overlap. Continue reading →

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