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Generate true random numbers on microcontroller

Sometimes there is really a problem of how to generate truly random numbers using your microcontroller. Usually, a computer processor or any other MCU can generate a Pseudo-Random Number (PRN). These numbers are generated by algorithms, so-called Pseudo-Random Number Generators (PRNG). Everything that a pure algorithm produces is predictable at some level. Many PRNG algorithms generate random numbers, but there is always a defined number of iterations when a random number sequence will repeat itself. Sometimes it may be acceptable. One popular way to generate pseudo-random numbers is using Timers. The universal algorithm is the concept of the Linear Feedback Shift Register (LFSR). LSFR is an n -bit register initiated with a non-zero seed value and is clocked by shifting values to the left and loading a new bit into bit0. The new bit is calculated by XORing the bits of selected taps of LSFR. This method is used in rand() functions.

Neural networks and artificial intelligence in robotics

When talking about artificial intelligence(AI), many people think that neural nets should be as intelligent as the human brain. Some people don’t even imagine how widely they are used in their life. Let’s narrow us to something more simple and understandable. The most exciting usage of AI is robotics. Today isn’t tough to build a simple robot with a few sensors and a couple of motors. But the harder part is to make it react to the real-world as you expect it to be. When programming the robot brain, there is checking sensor states and reacting to particular circumstances like hitting the wall, line on the ground, etc. But more sensors robot has more complex reactions may be. Programming of more complex systems may be painful without using simple neural networks.

AVR-DDS signal generator in-line ASM explained

I have got a couple of questions (in fact, not the first ones) for the AVR DDS generator I have built: “that’s all the asm code that I don’t understand. Could you explain it? Is it possible to do it with inline asm (only in C)?” I decided to explain this part more deeply because it took me to figure this all out. First of all, what we have to do, it is to implement simple DDS algorithm. In a few words, Direct Digital Synthesis(DDS) is known as a Numerically Controlled Oscillator. Simple rule: NCO-based DDS is a point(memory location)-skipping technique (and a constant interpolation of the stored signal) and runs at continuous update(clock)-rate. As the DDS output frequency is increased, the number of samples per waveform cycle decreases. Practically speaking, let’s have some math. We have a clock generator connected to MCU. In my case, F_CPU=16000000Hz. This is our Clock In.

Alternatives of MAX232 in low budget projects

Sometimes when you work on low-budget projects or don’t want to go shopping for max232 or similar IC, you can save your time and money by using other TTL to RS232 converter. We usually used to use a MAX232 chip like this: Max232 IC is a specialized circuit that makes standard voltages as required by RS232 standards. This IC provides the best noise rejection and very reliable against discharges and short circuits. If your project is more advanced and has to reliable you must use specialized RS232 to TTL converter IC’s. As I said Specialized is more expensive than other solutions.

Easy H-Bridge on MOSFET IRF7105 transistors

I think I don’t have to explain what is H-Bridge circuit. Well, it is mainly used to drive DC motors that they could be run forward and backward. The circuit is often used in robotics. Usually, there is a need to build a small, powerful, and with good characteristics H-Bridge. One solution is to use IRF7105 p and n channel MOSFET pair coated in the SO8 SMD case.

More about microcontroller oscillators

The choice of the microcontroller oscillator depends on many factors. Before choosing one, you should consider Cost, accuracy, and environmental parameters. Clock sources can be grouped into two major groups: mechanical resonance(crystals and ceramic resonators) and RC (resistor, capacitor) oscillators. The most popular form of mechanical resonant generators in microcontrollers is Pierce oscillators: Ceramic and crystal-based generators provide very high accuracy and low-temperature coefficient. But they have a slower startup comparing to RC generators. But the RC generator’s precision suffers from temperature variations and supply voltage. Nominal frequency can variate from 5% to 50%:

Connect Nokia 3310 LCD to LPT port

I found this circuit really simple and interesting. It is effortless to drive Nokia 3310 graphical LCD using a simple LPT cable and some PC software. First of all, connect graphical LCD to LPT port according to the following circuit: The graphical display needs about 3.3V of supply voltage, while LPT gives about 4.5 -5V. This is why diodes are used to reduce voltage by the fo犀利士 rmula: Continue reading

High capacity multimedia cards in embedded systems

Multimedia cards are popular around us. There are well known Compact Flash, CD, MMC Memory Stick. Usually, when you make a new design with external memory, you consider EEPROM or Flash ICs with some capacities with up to a few Mb. But why limit yourself? Because in some cases, it is smarter to add a multimedia card socket and use any capacity (even a few Gb) multimedia cards in your projects. Using removable storage cards you get few advantages: You can share data from your card with any device that has a reader; You can have any size of storage memory; Easier to get one than specific IC; Cost-effective; I really like Using multimedia cards because you can get huge amounts of storage of price small EEPROM or Flash IC. They are cheap because of mass production. They are available everywhere: digital cameras, Mobile phones, personal players, etc. Another advantage is that you can store data in a format that the PC understands. This way, it is easy to collect data for later analysis using PC software.

RS-485 interface for connecting multiple devices

RS-485 is an updated version of the RS-422 interface. It is designed to communicate between multiple devices connected to a single data line. Standard allows connecting 32 transceivers to the data line. This is achieved by using tri-stable drivers that are separately programmable. This allows only one device to work at a given time. Resistors used in the circuit are so-called termination resistors for matching the transmitter and receiver impedances to avoid reflections. The matching resistor depends on the cable used but is 120Ohm.

RS-422 interface basics

RS-422 is a standard for serial data transfer similar to RS-232, but it uses the difference between two lines (RS-232 uses a reference to ground). RS-422 uses twisted pair (difference pair) to represent the logic level. Such data transmission type is so-called balanced transmission as it is not referenced to ground. This is a noise-proof solution because the same noise affects both lines, which are differentiated out. This allows carrying data at much longer distances at higher data transfer rates. RS-422 can transmit data to up to 1200metters. The maximum transfer rate can be 10Mbits/s. 120Ohm resistor acts as a terminal resistor that removes reflections, that may occur during transmission over long distances. Voltage levels between twisted pair lines are 4V and between transmission lines is 12V. RS-422 can be compatible with the RS-232 interface by simply connecting the negative wire of the twisted pairs to the ground.