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Avoid smoke with power protection circuit

When designing an electronic device, you want to make sure that it won’t go in smoke under unexpected circumstances. You never know what may go wrong during the device’s lifetime, primarily if it is powered from mains. The small circuit between your battery and device may protect it from mistakes like reverse power polarity. His lists start with a simple series diode, which is cheap but may help protect from reverse polarity. Like any other, it has a downside – voltage drop (0.7V) that may be a pain for low voltage devices.

AVR GCC LCD library allows connecting pins in any order

Probably some of you are struggling in finding a proper LCD driver that would work on any circuit. I just wanted to point out that I found some time to improve my current LCD library to support a mixed pin connection case. Earlier, you had to connect LCD in a pretty strict way where pins had to be aligned and attached to a single AVR port. Sometimes this can’t be done for various reasons – you want to use those pins for other alternative functions, or you want to trace your PCB better, etc. In this updated version of the 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 and any port. A couple of examples should give some clue on how to start using it. If you used this library for some project, you only need to modify the header file while the project source code can remain the same.

Modeling of analog part for DDS3 signal generator

When building an AVR DDS2 signal generator, there were many discussions about signal conditioning in the analog part of the device. The first argument was that LM358 wasn’t the best choice for this purpose. Another one pointed to the sine wave that wasn’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 asks for a better analog part. Some people suggested replacing LM358 with OPA2134, but it seems to be quite an expensive choice. In my opinion, low noise, a general-purpose op-amp can be great too. I’m going to 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 the same reasonable price.

Multivibrator – back to basics

Multivibrator circuit is one of the first projects you start learning electronics. It is a beautiful circuit widely used for educational purposes and even in end projects as waveform generators. Lots of hobbyists grab a microcontroller/Arduino to blink LEDs. But using basic circuits like multivibrator may be cheaper, faster, and even fun. [Ray] decided to go through multivibrator theory and explain its working in detail step by step. The circuit itself consists of two transistors, two capacitors, and four resistors. When powered, the circuit generates a square wave signal that can be used to flash LEDs or clock other circuits. You will get an intuition on what causes multivibrator to develop generate. Formulas allow calculating resistor and capacitor values for a particular frequency. If you are a starter in electronics, build one on a breadboard and do some experiments, why not start with Christmas lights.

Driving Graphical LCD with STM32F103ZET6

STM32F103ZET6 board comes with 3.2 inches graphical LCD which features an ILI9320 controller. Equipped LCD is capable of displaying 252144 colors when driven in 18-bit mode. We are going to run it in 16-bit mode, so we are limiting it to 65K colors. LCD driver is based on the existing code found on the internet, originally developed for the STM3210E board. Only minor modifications were needed, like assigning the proper control pins.

Connecting STM32 USART to standard I/O streams in GCC

In many situations, when working with STM32 microcontrollers, you will want to output text strings. There is no need to write specialized functions that output specially formatted strings as it is hard to keep up with various cases. It is convenient to use standard I/O streams and their library functions that allow sending formatted data streams. Arm GCC toolchain comes with the newlib C library from Redhat, so it isn’t specially designed for the embedded toolchain. To use stdio functions, we have to take care of several syscals so-called “stub functions.” These functions usually are provided by operating systems like you would write C programs in Windows or Linux. In our case, we aren’t using any OS, so 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 the internet. I noticed that it was written for STM32 Discovery. I named it newlib_stubs.c and placed it in the startup directory. Among system functions implementations like _write(), _fstat(), etc., there are also USARTs assigned to standard streams:

Interrupt based button read on STM32F103ZET6 board

In the previous example, we implemented a simple demo program that reads buttons by continually checking their status in the main program loop. This isn’t an efficient and convenient way to do that. Imagine your application 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 an advanced interrupt system that is pretty easily manageable. All interrupts are controlled inside Nested Vectored Interrupt Controller (NVIC), close to the Cortex core, to ensure low latency and robust performance. Main features of NVIC include:

Implementing buttons on STM32F103ZET6

Last time we have made a good starting point with setting up a project template for the STM32F103ZET6 development board using GNU tools. Using the same project template, we can move forward and start programming other elements. This time a quick note about adding a button library. This is a modest implementation that initializes port pins and then reads their status. The Development board is equipped with four user-programmable buttons named WAKEUP, TAMPER, USER1, and USER2. We will not care about the meaning of names; use them as general-purpose buttons for now.

Driving LEDs with LPC2148 microcontroller

The LPC2148 development board is a mighty board with an ATM7TDMI series microcontroller considered an old guy compared to Cortex ones. But still, these are widely used and are powerful. The Development board has some handy features installed. 12MHz crustal allowing to run the 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 a serial-in parallel-out shift register, 2×16 LCD, buzzer, audio jack with an amplifier, two programmable buttons, and 256Kb of I2C interfaced EEPROM. The 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 a great board for prototyping and end application.

LED blinky demo on STM32F103ZET6 development board

I found some time to play with the STM32F103ZET6 development board and decided to set up a simple project for it. The trickiest part of this is to set up a project environment that would serve as a template for the following developments. Many ARM developers chose the CodeSourcery Lite edition toolchain. It has full command line functionality – this is what we usually need. If you want some alternative – you can select gnu yagarto ARM toolchain, which is also great and free. No matter which tool you select, the code will work on both. Let’s stick to CodeSourcery. Just download it and install it on your PC. As we said Lite version supports only command-line tools – we need an interface for it. Eclipse IDE is one of the favorite choices, so that we will grab this one too. Yagarto website has an excellent tutorial on how to set up the Eclipse IDE in a step-by-step manner. We won’t go into details with this.