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AVR controlled signal generator design considerations

A signal generator is a second must-have tool after oscilloscope while working with electronics designs. I don’t have any signal generators, so I decided to make one. This is gone be a simple AVR-controlled signal generator. I’ve chosen the Atmega8 microcontroller as this is the simplest one of Atmega’s series microcontrollers. It has 8kB flash memory. This is an initial post of the project. I have only designed a schematic and PCB board. I’ll be adding project progress in further posts. A little bit about AVR controlled signal generator. This is going to be a stand-alone generator coated in a 100x60x35mm metal box, the one I’ve found in my drawer. It will be powered by a 9V battery (through a 7805 voltage regulator). Controlling will be done with a series of buttons on the box side. And the information will be viewed on the 2×16 LCD screen on top of the box.

Atman AVR kick start

Atman AVR is an integrated c/C++ compiler IDE for Atmel AVR microcontrollers. AtmanAvr C development environment includes ProjectWizard, CodeWizard, Workspace, Output, Text editor, Binary editor, Debugger. The compiler itself is a GCC compiler for AVR. The only thing that makes it commercial is the integrated environment: ProjectWizard – lets you customize a project through series dialogs, and then it generates initial code automatically; CodeWizard – helps in programming routine tasks like creating new modules, adding functions navigating; Advanced workspace where you can find File View, Class View, and I/O View, and many more. If you would like to try this IDE, you may download AtmanAvr C IDE from the manufacturer’s site https://www.atmanecl.com. Bellow is an Atman AVR kick start guide with some screenshots: Create new project File->New: In the Project Name enter the name of your project. Also, select where your project will be located. From tab Projects select one type of projects:

Tradeoff between DC motors and stepper motors

This is a small comparison made between three types of motors: DC motors and stepper motors. Let’s see what their cons and pros are: Stepper motors don’t require feedback to determine position. The microcontroller determines the position by sending pulses to stepper motor; When the load is too high to the stepper motor, then it may stall, and there is no way to report this to the microcontroller; DC motors with feedback can report stalls on high loads or other conditions; Stepper motor has no brushes – there is no EMI; Stepper motor may produce full torque – this enables them to hold the rotor in the desired position; DC motors deliver more torque at higher speeds than stepper motors; Stepper motors can produce low speed without loss of torque. Dc motors lose torque at low speed because of low current;

I2C EPROM programmer

Sometimes you need to program I2C EEPROM chips and don want to invest any bucks in it. Then you should consider the I2C EPROM programmer originally designed by Claudio Lanconelli. This is very easy to build and use circuit but it supports 24C01, 24C02, 24C04, 24C08, 24C16 24C32, 24C64, 24C65, 24C128, 24C256, 24C512 I²C Bus EEPROM, auto-detects 24XX EEPROM capacity For the I2C EPROM programmer, you need to download PonyProg programmer software from www.lancos.com. Choose “Easy I2CBus” from the Options – Setup menu and the parallel checkbox on WindowsNT/2000. You have to select “AVR ISP I/O.”

Serial Peripheral Interface – SPI Bus overview

Serial Peripheral Interface is a simple interface that enables communicating microcontroller and peripheral chips or intercommunicating between two or more microcontrollers. Serial Peripheral Interface Bus, sometimes called four-wire interface, may be used to interface such chips or devices like LCD, sensors, memories, ADC, RTC. The range of usage is huge. SPI Bus uses the synchronous protocol, where transmitting and receiving is guided by a clock signal generated by the master microcontroller. SPI interface allows connecting several SPI devices while master selects each of them with CS (Chip Select) signal – (Underline means that active is LOW). SPI bus consists of four signal wires: Master Out Slave In (MOSI), Master In Slave Out (MISO), Serial Clock (SCLK or SCK) Chip Select (CS) for the peripheral. Some microcontrollers have a dedicated chip select for SPI interfacing called Slave Select (SS). The master generates a MOSI signal – the recipient is Slave. MOSI may also be labeled as SI or SDI. Slaves generate MISO signals. In some chips, you might find labels SO or SDO. SCLK or SCK are generated by master to synchronize data transfers. CS (SS) signal is also generated by master to select slave chip or device. Data transfer is…

7805 voltage regulator for your design

This is the most common voltage regulator that is still used in embedded designs. The LM7805 voltage regulator is a linear regulator made by several manufacturers like Fairchild or ST Microelectronics. They can come in several types of packages. For output current up to 1A, there may be two types of packages: TO-220 (vertical) and D-PAK (horizontal). With a proper heat sink, these LM78xx types can handle even more than 1A current. They also have Thermal overload protection, Short circuit protection.

Using VMLAB as virtual oscilloscope

VMLAB is one of the well-known simulators. This is a software simulator of AVR and ST62 microcontrollers. The simulation is far away from real-time, but All timings are tied to real-world values. VMLAB is designed to work as a project. This is a special language (script like), where the circuit is described – where are connections between hardware and microcontroller defined. You may find few prebuilt examples in folders C:\VMLAB\AVR_demo and C:\VMLAB\ WinAVRdemo (If your installation is in C:\VMLAB\ folder). VMLAB is rich in its hardware support: Resistor, Grounded capacitor, Interactive switch/key, LED, Pulsed voltage source, Sine wave voltage source, Slider dependent voltage source (interactive), Non-return-to-zero (NRZ) generator (interactive), Operational amplifier, Comparator, 2 inputs NAND gate, 8 bits D to A converter, RS232 based TTY (interactive), LCD module, I2C monitor (interactive), Interactive keypad 4×4 Multiprocess-dedicated: External Input, External Output. So you can do a wide range of simulations. VMLAB also has a powerful scope where you can watch voltages on pins or even some internal microcontroller resistor values like ACO, TIMOVF signals. Let’s make simple project using VMLAB tool. Start VMLAB And create new project by selecting Project-New. Select project properties like project location, c file name, microcontroller type, software…

Frequency response of discrete system

In the previous post, we discussed the impulse response. Impulse response h(n) is a digital system response in the time domain. But there is another characterization of the discrete system – frequency response H(ejω). Frequency response can be calculated form impulse response by formula: This means frequency response is the systems transfer coefficient to every frequency value. Frequency response is a complex function. So this can be evaluated as:

Digital system equation

Back to the DSP thread. Let’s talk about the digital system equation. Every digital system can be described using this equation. The output of the digital filter generally consists of previous inputs and previous outputs. y(n-k) is considered as previous outputs; x(n-p) – previous inputs; ak and bp – coefficients; This equation is convenient to define the discrete systems and extract various characteristics. Number N defines a discrete filter tap (Tap – A FIR “tap” is simply a coefficient/delay pair). Lets say we have digital filter made of one tap. y(n)=a·y(n-1)+b·x(n) First we calculate filter response function – h(n): Response function is calculated from system reaction to discrete impulse ´(n). So assume that x(n)= ´(n) and y(n)=h(n). Initial conditions: y(-1)=h(-1)=0. Then: h(n)=0 when n<0; h(0)=a·h(-1)+b·´(n)=b; h(1)=a·h(0)+b·´(1)=ab; ……. h(n)= ban where n>0 Lets say we have a=0.7; b=1; Then we get discrete system characteristics: This equation in example describes IIR (Infinite Impulse Response) discrete systems because there is a feedback element a·y(n-1). There is another type of discrete filter – FIR (Finite Impulse Response) Finite response filter equation is much simpler: As you may notice from the equation – the IIR filter has an infinite number of response impulses while the…

AVR microcontroller interrupts using WINAVR

I can’t imagine a microcontroller without interruptions. Without interrupts, you would have to make loops to check if one or another event occurred. Polling has many disadvantages like programs have to make loops, which takes valuable microcontroller resources. These resources may be used for other data processing tasks. This is why the microcontroller comes with built-in interrupt support. Instead of checking events, the microcontroller can interrupt normal program flow and jump to interrupt the service subroutine. During an interrupt, the microcontroller stops the task at the current point, saves necessary information to stack, and gives resources to interrupt the subroutine. When interrupt subroutine finishes, and then normal program flow continues. In assembler your program would start with interrupt table: After the table goes the main program (RESET) and other interrupt subroutines where the program jumps after the interrupt occurs.