delabs Circuits

Wednesday, January 21, 2009

Digital and Embedded Systems Design

An Embedded Microcontroller or DSP system is made of Chips, Circuits and Firmware. The digital voltage levels, speed, bus width, fan out, power consumption are some factors that a designer has to keep in mind. As portable and wireless gadgets are becoming more popular, RF, Ethernet and Energy Efficient Design aspects should be studied. Power electronics and Analog Circuits knowledge is used around the system, all this is integrated to make an instrument, equipment or gadget.

Digital and Embedded Systems Design
  • 80C51 ports can sink more current but source very less, hence use a 10k pull up at all the ports or outputs.
  • Firmware must be developed in increments, tested in increments, backed up in increments, must be modular (include) reuse.
  • Tristate output, High Impedance and Floating all mean the same when it comes to IC Inputs-Outputs. It means the pin is insulated from rest of circuit in the IC. That means it will not influence the node or bus it is connected to. A DMM terminals are floating means that the hand held plastic DMM has no electrical conductive link to earth or ground.
  • You can use hyper terminal to upload code to single board computers 80C51 like in BINARY or ASCII. 
  • ASICs are for large volume production, or for products which have a long product life cycle.
  • Low volume production use FPGA or CPLD, or even flash based microcontrollers, so that all your inventory can be reused and recycled.
  • Cell phones or a LAN card ASIC is ideal as volumes are good in cell phones and for LAN cards the technology is matured. For either FPGA or ASIC's you get IP Modules or Code Libraries for many functions and applications.
  • Whatever the method keep design flexible and modular for reuse and to save cost. remember the hardware is difficult to alter, software can be altered even at customer site, flash has made this possible
  • In the future chips may be both analog and digital programmable with flash.
  • Some FPGA, CPLD, ASIC links, WinCUPL, Design and Reuse, fpga4fun.
  • Unused CMOS inputs should have a pull up or pull down resistor, it should not float, or it oscillates.
  • Have a decoupling capacitor 104 that is 0.1uF or 100nF across the supply of every IC very near the IC supply pins.
  • A watchdog timer should be used in every microcomputer circuit like 8051 so that the system resets on hanging.
  • The reset on a microcomputer should be applied till the supply to it is stabilized, this will enable a clean start.
  • Analog ground (opamps), digital ground (CMOS) and power ground (relays and LED) should be separate, (linked at root)
  • Pull up or pull down resistors in TTL can be 10K and in CMOS 100K and in battery operated systems 1M.
  • CMOS gates and Opamps have a output drive capability of ~ 10-20mA, so when you drive a load say an LED use a series resistor to limit the current to 5mA to 10mA.
  • When the number of digital chips you use in a project goes above 20 or 30 then it is better to use PLD or CPLD types from Altera, Xilinx or Lattice etc.
  • Try to use same family ICs in a circuit, like only LS or only HCT, if you mix up then you have to do a design review.
  • In a industrial environment many motors, DC drives and AC drives will be running, this will produce EMI, RFI, kickback spikes which cause microcontroller based equipment to hang. Use a watchdog timer for uC.
  • More EMI immunity by using opto couplers for all input and outputs, 4-20mA current signals for input and output and an isolated wide range SMPS.

Contents

Basic Electronics
Basics of Electronics
Product Production
Work Discipline
Testing Points
Learning Electronics
Electronics Theory

Production Notes
Prototype Fabrication
Electrical Circuits
Electromechanical


Library
Scots Guide Electronics
Engineering - Wikibooks
Design Lab - Jim Svoboda
DC Circuits UOG
Socratic Electronics
Blobz Guide Electric Circuits


Product Design
Product Development
Constant Current Source
Good Voltage Regulators
Insulation Resistance
Digital Insulation Tester
DN Schematic PCB 04
DN Product Design 07


Hobby Circuits
VU Meter Circuits
LED brightness control
555 Incredible Chip
Process Control
liquid level measurement
Thermocouples and RTD
Design ADC Interface uC
Thermocouple Amplifier
IA Instrumentation 02
Temperature on DMM
Optical Proximity Switch
Analog Mux - Data Acquisition


Test Measurement
Instrumentation Automation
NI Test and Measurement
DMM Digital Multi Meter
Oscilloscope in T&M
IA Automation 01
Build Instruments
Tektronix T&M Equipment
Educators Corner – Agilent


Power Electronics
UPS Background
Transformer Connections
DN Power Electronics 03
DN Power Electronics 02
Half Bridge Convertor SG3525


Embedded
Interfacing Microcontrollers
Embedded Process Control
80C31 8052 Microcontroller
Microprocessors and uC
Embedded Systems Design

Components
Good Voltage Regulators
Relays and Contactors
Potentiometers Trimpots
Prototype Boards Types
Types of Capacitors
Types of Switches
Resistors How they Work
Coils Transformers SMPS
Mains Transformers Types
DN Components Selection 05

Tutor Gadgets
Count-Up Timer
Digital Logic Gates
Electronics Tutors

History
Teaching Instruments
Charles Proteus Steinmetz
Muntzing a Circuit Design
Teralab Electronics projects
Historical Instruments


Tables, Charts, Videos
Binary and Hex
Resistor Color Code
Ohms Law
Giga, Tera, Pico, Nano
High Resistance Materials

Analog
School - Analog Design
DN Analog Basics 06
DN Op-Amps 01
TI Semiconductors