Design Notes 2005

• Most pots have a dielectric insulation between metal pot shaft and terminals of 1KV or more. Some commercial pots may have lesser breakdown voltage and that will be a product safety issue. So either way use Plastic Knobs or pots with plastic shafts.
• Design the product in such a way that neither the pot terminals or pot switch is used for mains voltage, instead use the pot switch or variable resistance for signaling and the mains can be switched with Relay or Thyristor.
• Unused high impedance inputs of opamps or gates or any IC should be pulled-up or down.
• High Impedance inputs which have to float can be made noise immune with a small cap to ground. Like a 102 CD.
• Revise your electronics basics and theory at Doug Gingrich's PHYS395 Course.
• If an opamp circuit with feedback oscillates, then a cap at the right place can stop it, it will dampen the oscillations, just like eddy current dampening in moving coil meters. One way is a cap across the feedback resistor another way a cap between inv- and non-inv+ inputs. A closed loop system may oscillate at border points. The value of cap depends on how fast (response time) the system has to be and the type of oscillations seen.
• Hysteresis is like on at 300 off at 304 like in heaters or air conditioners. If you on-off at sharp 300 there is a chatter or oscillation. This is called dead-band in temperature control. In above example 304-300=4 is the dead-band.
• Do not club Heatsinks unless the heatsink is very big or the clubbed components form a part of a current sharing set. If you club say two TO220 devices one dissipating 10W with a 2 Watt heating device, you may reduce reliability of the 2W device. Then clubbing parallel current sharing devices on one heatsink may be a good idea as it may reduce thermal runaway, also parallel power transistors should each have 0.1E in emitter path, this also can force load sharing on lazy devices.

Testing and Design Points

• MOSFET needs a turn on pulse and a turn off pulse as gate capacitance is huge.
• NTSC is like 320 x 240 pixels, which is TV, which is lower than your computer's 800 x 600.
• Do not use an oscilloscope to measure 230V directly, use a transformer, differential probe or attenuator.
• An oscilloscope 1M probe or a DMM 10M impedance can load circuits with nano-pico amps of bias.
• Red socket and probe for positive and black socket and probe for negative
• In schematic indicate pin numbers of every IC or map the correct part if manual place and route is used.

If the waveform on the scope droops then you may need to use a 10X attenuating probe or mode. this attenuator is at the tip of the probe hence better measurement possible, also very high frequency signals may be best transmitted over a 50 ohm impedance matched line to the Oscilloscope. The History of Oscilloscope, Learn more about Oscilloscope from the Innovator of the Scope as a Measuring Instrument here is XYZs of Oscilloscopes.

Is it oscillating ?.... We cannot say, it could also be DC, you need to see if a Clock is present. use a signal tracer or a DMM freq mode, or AC measurement. or build this solorb.com-elect-logprobe. When you do not have a scope you can build one for the PC.

• PC Oscilloscope
• Sound card oscilloscope and spectrum analyzer
• Oscilloscope and Spectrum Analyzer products from Pico
• PCS100 is a digital storage oscilloscope
• Digital Storage Oscilloscope Adapter Mk3
• Digital Oscilloscope

Polarity and Zero Cross
radio-flier.com-opamps.html see the last circuit it is a polarity indicator, which will tell you to swap the leads. VRS Zero Crossing detector circuit, Zero Crossing Detectors, Comparators, Discover Circuits - Zero Cross.

Analog Notes

LM335-336 -

LM335 is a temp sensor, LM335 . use it for temp for CJC. Temperature Sensors - RTDs and Thermocouples, - Chapter 6: Temperature Measurement, LM336-2.5 is an voltage Reference.

Current Loop

4-20 ma will drive DC drives, motors and steam valves. It is a current loop, for long distance transmission, current loop is not prone to noise and hum EMI RFi. As it is a power transmission no loss of data. also many equipments can be in one data loop. a single transmitter with 4-20mA out can driva a recorder, motor, controller and SCADA. all in a series loop.

Current loops, - Current loop - Wikipedia, the free encyclopedia, - 4-20 mA - Wikipedia, the free encyclopedia

Opamp Types

TL062 any equivalents ? -- LF353, TL072, fet input. 1 tera ohm input imp. OP07 costly 1 giga ohm. LF353 pin to pin replacement of TL062 72 and 82. LM358 will work but error as it is 1 meg. OP07 75uV offset. quad LM324 can work of batteries well. all work best with dual +/- 5 V or more. 7805 / 7905 is ok ? -- yes.

OpAmps, - 741 Op-Amp Tutorial, op-amps, Operational Amplifier
Analog Electronics: Basic Circuits of Operational Amplifiers

Persistence of Vision

When the frequency of flicker of a LED is higher than persistence of vision 20-30 mS, then it will not show, just like TV or movie. Say 70Hz you see a flicker in display. At 300 Hz you may not.

Persistence of vision - Wikipedia, the free encyclopedia
teachers.oregon.k12.wi.us-bdn-history.html

Product Development Fundamentals.

1. Product Design Sections :

a.	Electronic Engineering	Circuit Design, PCB Design, EDA.
b.	Mechanical Engineering	CAD, Tool and Die Design, Enclosure
c.	Software Engineering Firmware	PC ware, CASE, emulators

2. Methods of Product Design :

a.	Design Automation.	Design and Simulation with Computer.
b.	Computer Aided Design	Design on Computer, Breadboard test.
c.	Conventional Design.	Paper design with Breadboard test

3. Criteria of Product Design :

a	Ergonomics	User friendly Interface of controls, display, etc..
b	EMI / RFI Ext.	Immunity to external electrical disturbance.
c	EMI / RFI Int.	Reduction of Internal electrical noise generation.
d	Input Cost	Selecting Cost effective components and methods.
e	Product Safety	Eliminating shock hazard, fire hazard or stress.
f	Corrosion res.	Resistance to Chemical Fumes, brine, gases etc..
g	Reliability	Long Life reliability engineering, MTBF, stability.
h	Serviceability	Accessibility - Maintenance and repairs, Self test.
i	Vibration	Enclosure / Components to be vibration resistant .
j	Ease of Manfr.	Manufacture ease and provision for test and Calib..
k	PC Interface	RS232, GPIB, etc. for PC Control and recording.
l	Upgrade Ease	Options, Software change, Hardware upgrades.
m	Quality	Design, Components, Production methods.
n	Accuracy	Specifications of performance and its stability.
o	Misuse-Abuse	Rugged design both electrically and mechanically.

4. Criteria of Circuit Design :

a	Technologies	Time proven technology and Standard Parts.
b	Reliability	Component Selection and Design Methods.
c	Modular	Allow for incremental upgrades and Service.
d	Safety Margins	Overrating for Voltage, threshold, speed, etc..
e	Testability	Test Points, Isolating Jumpers, self test mode.
f	Isolation	High voltage isolation, User safety, grounding.
g	Thermal Limits	Dissipation Limit, Heatsinks, Shutdown, Size.
h	Protections	Fuses, Current Limit, Zeners, Varistors, Alarm.
i	Power economy	CMOS Designs, LCD Designs, SMPS, Portable.
j	Electrical Parts	Connector selection, Relays, Switches, PCB.
k	Precision	Accuracy, Resolution, Drift, Thermal stability.