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Interfacing PC keyboard to AVR microcontroller

Properties: Interface AVR to standard PC AT keyboard; Only two I/O lines were used. One line is also connected to the external interrupt pin of AVR; No external components are needed for the interface; Included C source reads from keyboard interface and converts to serial In many situations, you need some human interface for your microcontroller project. In this example is interfacing AVR microcontroller to standard PC AT keyboard described. Physically interface looks as in picture bellow: In a keyboard interface, signal lines are an open collector with pull-up resistors.

Clockless CPU design

Clockless CPUs are so-called asynchronous CPUs where are not clock generator needed, which clocks every synchronous operation. Asynchronous processors give results, not after a defined number of clocks, but after it finishes operations. This is a key to effective energy usage, and asynchronous processors generate less noise than synchronous. Asynchronous processors have couple advantages against synchronous: Components can run at different speeds inside a clockless CPU, while clocked CPU components are tied to a clock generator. Clockless CPU operation stages don’t depend on clocks and can be finished faster than normal, and there is no time gap between stages as there is no need to wait for the next clock cycle. For instance, it can show the operation results rather than waiting for the next clock cycle like it is in a synchronous CPU.

Embedded RTOS System

RTOS ( Real-Time Operating system) is a programming environment that interfaces hardware and desired tasks. RTOS usually has a built-in set of services (interfaces and functions) that allow interaction between tasks and hardware. Because most low-level functions are performed by RTOS, the realization of programs becomes much easier. What is the difference between Embedded RTOS System and a regular OS (Operating System)? The main difference is that RTOS performs tasks according to reaction time on one or another event. Many microcontrollers have the ability to support one or another Real-Time Operating System.

Connect 6 LEDs using 3 microcontroller pins

Sometimes you need more than you have. I am talking about microcontroller pins. You have to connect 6 LEDs, but you have only 3 microcontroller pins available. To use another microcontroller isn’t always a solution using decoder circuitry isn’t necessary as well. There is a simple hint on how to do this: Connect diodes to the microcontroller as follows: Now, look – if you set one pin to “1” and second to “0” (leave third pin high state – as input pin), then only one led lights on. You can light two LEDs by setting the third pin as an output and state “1” or “0,” which depends on which LED you want to light.

Testing Your Embedded System

Every time you are making some circuit or more complex system, you always do some testing to ensure that your electronic creation is working properly and exposing it to publicity. Let’s say you are constructing some robots. Then a typical list of the testing task may be as follows: Stability tests using various working modes and critical supply voltages (like 4,75 and 5,25V); Start-up testing purpose is to check system readiness to accept commands after power-up; Checking correctness of executed commands; Checking correctness of sensors; Sometimes you will need to prepare good documentation where every node reliability is calculated. Also, testing methods of each node may be included in the documentation. Of course, many devices may work in a wider range of supply voltages, but there are always some electronic components that need more than 5% stability.

Microcontroller Brown-out detection

Mostly all microcontrollers have built-in Brown-out Detection (BOD) circuit, which monitors the supply voltage level during operation. BOD circuit is nothing more than the comparator, which compares supply voltage to a fixed trigger level. If the microcontroller doesn’t have an On-Chip Brown-Out detector, then there can be an external circuit used : In the image above, there is a discrete brown-out detector circuit. There are particular IC where additional delay circuitry and hysteresis used to normalize supply voltage may take some time in a real word. Such ICs are cheaper than one built from discrete components.

Radio Frequency Identification RFID

There are two types of RFID devices: Active and Passive. Active devices have a power source built-in, which supplies the transmitter. The transmitter is triggered by sending the signal to an RFID device. These devices have their own code and can transmit signals in desired time intervals. Active RFID devices are good in defining locations of objects or sending some information about a particular place (RFID-based location determination). Active RFID devices use high frequencies (455MHz, 2,45GHz, or 5,8GHz) – working range about 20 – 100 meters. The most common are passive RFID. They don’t need a power source. Passive RFID devices are low frequency(124 – 135kHz – low) and high(13,56MHz – 960KHz – high; 2,45GHz – UHF). The working principle of low and high-frequency devices differ. Simultaneously, low-frequency readers generate a magnetic field that induces a current in the RFID device antenna. The chip inside the RFID device modifies this magnetic field, which is reread by the reader. The working distance of such a device is about 35cm.

What is surface mounting?

Simply talking surface mounting is a soldering technology where the component is soldered directly to a series of solder pads called a footprint. It is different soldering technology from through-hole, where component leads are inserted into holes of the board. The footprint is a series of pads that conform to the lead layout of packages of surface mount devices (SMD). Surface mounting has several advantages over through-hole technology. First of all the board become much smaller. So smaller boards and more dense placement of elements reduce costs. Because of higher placement density, traces between components becomes shorter. It lowers parasitic inductance and capacitance.

Control memory sections using AVR GCC

If you are programming AVR microcontrollers in C, usually don’t think about how the compiled program is stored in microcontrollers’ flash memory. The compiler organizes data in the way it looks optimal. But sometimes, you are working with programs where you need to code chunks located in specific program memory locations. For instance, I faced this problem while developing an AVR controlled signal generator. I wanted to make an efficient and compiler independent main loop where the signal has to be read from flash memory and transferred to port. I managed to use the inline ASM function, which does the job: The linker produces ASM code like this:

How to measure signal period using microcontrollers

Measuring the signal period is a common problem in embedded systems. This can be measuring the time between two events or measuring signal frequency f=1/T and so on. Measuring the time interval or period is based on comparing event time t with discrete-time usually produced by a timer. This usually is done by filling the event time t with discrete-time intervals t. According to this, the discrete-time signal period has to be much shorter than event time: t<< t. Then counting these short time intervals, we can determine the event time.