Still struggling with various PCB making technologies and cannot do it right, you should try Photo Etching method which is becoming more and more common among radio amateurs. All materials needed are easily accessed. Probably the hardest part is to obtain UV light source. But you can find tons of sources on the internet how to build one.
Finally second and improved AVR DDS signal generator is here. First AVR DDS V1.0 generator was only an attempt of running DDS algorithm without any amplitude control. This time I still wanted to keep things simple like minimum count of widely accessible components circuit, single sided PCB that comes together with good functionality.
AVR DDS signal generator V2.0 is a firmware based DDS signal generator which uses slightly modified Jesper’s DDS algorithm adapted to AVR-GCC C program as in-line ASM. Signal generator has two outputs - one for DDS signal and another for high speed [1..8MHz] square signal - which may be used for reliving microcontrollers with wrong fuse settings or for other purposes as well. High speed (HS) signal is direct output from Atmega16 OC1A(PD5) pin. DDS output is used for all other signals that are generated via R2R resistor network and is adjusted via LM358N offset and amplitude regulating circuits. Offset and amplitude can be regulated by two potentiometers. Offset can be regulated in range +5V..-5V while amplitude in range 0..10V. DDS frequency range is from 0 to 65534Hz that is more than enough for testing audio circuits and other tasks.
Main AVR DDS V2.0 signal generator features:
An embedded system is a type of computer that can perform a few specialised tasks. This design is contrary to the normal computer that is designed to perform a number of operations that are in many cases unrelated to each other. Embedded systems are present in many of the devices that are used today and act as their control units. The main issue with embedded systems is their optimality in the 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.
Here are a few characteristic features of embedded systems:
It seems that ATMEL do not want to limit the AVR branch with 20MIPS AVR microcontrollers. Recently they introduced new AVR microcontroller family - XMEGA - which is still based on AVR core but has a higher performance along with low power feature. AVR microcontrollers are really optimal where high performance is needed with relatively low code size. Probably XMEGA microcontrollers will fill the gap between standard AVRs and AVR32 microcontrollers.
XMEGA microcontrollers are featured with:
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 in to electrical signal shape. When signal has to be sent it has to be modulated.
Probably simplest and most common modulation method is pulse code modulation (PCM).
In CPM coding information is modulated as voltage levels. If supply voltage is 5V, then binary”1″ is represented as +5V while 0 as 0V level. Only two voltage levels are used to modulate signal. 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. Read the rest of this entry »
The processing of the various signals is carried out through implements that are together called as DSP hardware. This includes the hardware that is used for transmission of signals, various devices that are used to enhance or filter the signals, analogue to digital and digital to analogue converters and other processing equipment such as computers.
Among the hardware mentioned above, digital signal processors are the ones in which the actual processing takes place. 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 analogue signals as input, convert them into the digital form, process the signals and then, convert them back into the analogous form.
They make use of Direct Memory Access technique.
The term circuit technology usually refers to the various techniques that 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 a mechanical support for the various components present within the given device and also, the electrical connections between the components.
The electrical connections present on the PCB are made out of copper sheets that are 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 removal of unwanted copper. Some of them are:
The term Biosignal refers to all the signals that are being generated in the human body or any other living organism or more specifically it is used to represent all those signals from living organisms that are monitored to obtain certain useful information. Primarily, the term refers to signals that are electrical in nature but, some non-electric signals are monitored as well.
Typically, the changes in potential difference across a certain tissue in the body are measured in case of bio-electric signals. Let us have a look at few of the properties of biosignals generated by the human body that are analysed to obtain information:
Digital signal processing is the technique used to analyse various digital signals and obtain information form the same. It is also used for transfer of information from one place to another and also involves conversion in between analogue 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 that are generated by the different organs in the human body are measured in order to find information regarding the health of the same. For example, in 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 control unit of the device where they are processed and the necessary action is taken. For example, a device like the thermostat increases its resistance in proportion to temperature. This can be used to stem the current in a machine whenever the temperature rises. Read the rest of this entry »
These are devices that are used in electronic circuits to make reconfiguration of the same possible. The logical gates that are normally used perform a fixed function however, the Programmable Logic Devices (PLD) does not perform any predefined task when they are manufactured and need to be programmed before they can be used.
Before the introduction of PLDs, ROM (Read Only Memories) was used. EPROM that was available could be programmed by using any standard hardware for that device and hence, did not require any other peripheral hardware. Another advantage of ROMs is that a particular binary code stored in it could be obtained on any of the n output lines that were available in it. Thus, they can be programmed in any way one wishes to. However, ROMs have some disadvantages when they are used as PLDs. They do not produce the outputs as quickly as other devices; they are not very dependable as far as asynchronous inputs are concerned, they require more amount of power etc.
The first PLD was the programmable logic array that was developed from ROAM (Read Only Associative Memory) by modification of one of its metal layers and had 17 inputs and 18 outputs. Read the rest of this entry »
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