Voltage references in embedded design

Embedded systems that are dealing with DAC require good voltage references. Despite all voltage references having their nominal values, specific tolerances indicate how much values can vary from the nominal value. References, as a rule, are semiconductors that characteristics are affected by temperature. For instance, if we decide to use a 2.5V voltage reference then (Zener) diode LM336A-2.5 may be a good choice for this. These diodes have a low-temperature coefficient. It can guarantee that voltage will be in the range between 2.44 and 2.54 at 25ºC. This precise Zener diode has a third lead that can be used to adjust break down voltage. In the following figure, you may see a diode with a potentiometer where breakdown voltage can be adjusted in the range of ±120mV:

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Yet Another Simple AVR ISP cable

Probably this programmer cable can be found on every AVR fan website. It is straightforward and easy to build. You need a few passive components that can be packed inside the LPT connector. From my perspective, I wouldn’t recommend using this one ISP programmer if you are more serious about microcontroller projects because it has poor computer port protection. It connects directly to the LPT port without precautions. I recommend using a similar ISP circuit with buffer IC between LPT and target board. But let’s don’t pretend like we are brilliant. The whole beauty is in its simplicity. This thing does its job perfectly as long as the target board power supply is OK.

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USB bootloaders for AVR microcontrollers

Probably the most proper microcontroller programming method is using a bootloader program. Because you don’t need any special programming adapters or special knowledge – you need to connect a standard cable from your PC to the target board and run a special program on the PC which communicates with the MCU bootloader program. The idea is simple: If the microcontroller is preconfigured, then after reset, it starts running not from the start memory location, which is usually at 0x0000 address, but at some specific location, where usually bootloader lies.

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AVR DDS signal generator V2.0

Finally, the second version of the improved AVR DDS signal generator is here. THE first AVR DDS V1.0 generator was only an attempt to run the DDS algorithm without any analog amplitude control. In this DDS generator version, I still wanted to keep things as simple as possible using a minimum count of widely available components in the updated circuit. Also, I kept a single-sided PCB approach. AVR DDS specification AVR DDS signal generator V2.0 is a firmware-based DDS signal generator that uses a slightly modified Jesper’s mini DDS algorithm adapted to AVR-GCC C code as in-line ASM. The AVR DDS signal generator has two outputs – one for DDS signal and another for high speed [1, 8MHz] square signal – which may be used to bring back to life microcontrollers with wrong fuse settings for other purposes where a high-speed square signal may be needed. A high-speed (HS) signal is output directly from the Atmega16 OC1A(PD5) pin. The DDS output is used for all complex signals generated via the R2R resistor network and is adjusted via LM358N offset and amplitude regulating circuits. Two potentiometers can control offset and amplitude. The offset can be controlled in range +5V..-5V while magnitude…

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Embedded Systems: microprocessors and microcontrollers

An embedded system is a type of computer that can perform a few specialized tasks. This design is contrary to the normal computer designed to perform many operations that are unrelated to each other in many cases. Embedded systems are present in many of the devices used today and act as their control units. The main issue with embedded systems is their optimality in terms of cost, space and power consumption, etc., as there is no focus on increasing the functionality of the device. The term embedded system can thus, be used to refer to devices that perform certain specific functions and cannot be used to perform others by loading applications on them. Typical features of embedded systems Many of the embedded systems have several hardware restraints as they have to process real-time inputs and be safe to use. Others may not have some of these constraints, and thus, a reduction in the cost of the hardware used is possible. The term embedded system does not refer to isolated devices but rather, they are a part of the device they control or perform some other task in. The software that is used in embedded systems is usually termed firmware. The…

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Encoding and modulation of digital signals

We know that digital signals are stored as binary numbers in memory cells. Let’s see how these digital signals can be transferred, in other words – how they can be encoded into electrical signal shape. When the signal has to be sent, it has to be modulated. Pulse Code Modulation (PCM) Probably the simplest and the most common modulation method is pulse code modulation (PCM). In CPM, coding information is modulated as voltage levels. If the supply voltage is 5V, then binary”1″ is represented as +5V while 0 as 0V level. Only two voltage levels are used to modulate the signal. The signal can be sent in parallel (bus mode) or serial mode. In parallel mode whole (let’s say 8 bit) signal can be sent at once via 8 wires, while in serial mode, data has to be sampled in time. This transmission method is most popular in embedded systems. For instance, ADC sends converted data to DSP using CPM. CPM method is OK, but it has several drawbacks like the number of wires required for parallel buses. Still, probably the most dangerous problem is that transmission may experience skew problems when each data wire may have different time delays…

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DSP processors and their characteristics

The processing of the various signals is carried out through implements that are together called DSP hardware. This includes the hardware that is used for transmission of signals, multiple devices that are used to enhance or filter the signals, analog to digital and digital to analog converters, and other processing equipment such as computers. Among the hardware mentioned above, digital signal processors are the ones in which the actual processing occurs. Usually, the digital signal processors today have the following characteristics: They are equipped to handle real-time processing, i.e., they can give the optimal performance even when streaming data is being fed into them. The memories that are used to store programs are different from the ones used to store data. They do not provide hardware that supports multitasking. It can be used as a direct memory access device in supporting or host environments. They take analog signals as input, convert them into the digital form, process the signals, and then, Specific them back into the analogous form. They make use of the Direct Memory Access technique. The digital signal processors usually have architecture so as to optimise the following features:

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Printed Circuit Board (PCB) Technologies

The term circuit technology usually refers to the various techniques used in the manufacture of electrical circuits. A large number of devices that are used today make use of printed circuit boards (PCBs). These devices provide mechanical support for the various components present within the given device and the components’ electrical connections. The electrical connections present on the PCB are made out of copper sheets laminated on a non-conducting material. Initially, a large copper sheet is laminated on the board, and then the sections that are not required are removed. Various techniques are used for the removal of unwanted copper. Some of them are: Silk Screen Printing: In this technique, an etching-resistant ink is applied to those required areas, and the remaining part is etched off. Photoengraving: Here, a photomask of the circuit required is prepared using the desired software, and then it is applied to the blank PCB. After this, the portions that are not required are etched off. PCB Milling: In this technique, a mechanical milling system that can work on 2 or 3 dimensions is used to remove the copper. The milling system is controlled by software. In some other techniques, only the required copper is added…

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Biosignal Properties

The term Biosignal refers to all the signals generated in the human body or any other living organism. More specifically, it represents all those signals from living organisms that are monitored to obtain certain usage information. Primarily, the term refers to electrical signals in nature, but some non-electric signals are monitored. Typically, the changes in potential difference across a certain tissue in the body are measured in the case of bio-electric signals. Let us have a look at a few of the properties of biosignals generated by the human body that are analyzed to obtain information: Electroencephalography In the case of Electroencephalography, the activity of the human brain is monitored. Usually, at a synapse (junctions between the nervous system cells), the flow of ions occurs. This results in the formation of various signals that are used by the body to transfer information. The voltage variations caused by these signals are recorded, and thus, the brain’s activity is measured. Magnetoencephalography In Magnetoencephalography, the magnetic fields produced by the variations of electric currents that form the brain activity are monitored. For this, devices such as SQUID (Superconducting Quantum Interface Devices) are used to have high sensitivity. Many difficulties are faced one tries…

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Digital Signal Processing – Applications

Digital signal processing is the technique used to analyze various digital signals and obtain information from the same. It is also used to transfer information from one place to another and involves conversion between analog and digital signals. It finds its application in various areas ranging from broadcasting to medicine. Let us have a look at some of the applications of the same. Biomedical Applications DSP is used extensively in the field of biomedicine. In it, the various signals generated by the different organs in the human body are measured to find information regarding the health of the same. For example, in the case of electrocardiograms, the electric signals generated by the heart are measured. Similarly, the activity of the brain is monitored by electroencephalograms. Automatic Control These days, many gadgets are available that can perform their tasks automatically. These devices contain various components that can take inputs depending on the surrounding conditions. These are conveyed to the device’s control unit, where they are processed, and the necessary action is taken. For example, a device like a thermostat increases its resistance in proportion to temperature. This can be used to stem the current in a machine whenever the temperature rises.

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