Friday, April 20, 2018

Analog Level by BCD Thumbwheel Switch

BCD Thumbwheel Switch is used to input-set data in digital form, this can be read by digital circuits, uC and uP systems and PLC-SCADA Interfaces.

Temperature Measurement and Control

In the early transition of analog to digital, before uP became acceptable, Digital systems without uP were made, it even had printers, RAM and displays. The uP systems were coming in, uC had not yet come and uP systems had to still win the confidence of the Prudent Industrial Design Engineer.
The drawbacks of uP based systems used in Computers, in those days were.
  • Power Consumption was very high, needed SMPS.
  • Many chips, a CPU had a Retinue of many chips.
  • Large Board, Double or Multi Sided due to Bus.
  • Fussy, Hangs on minor Power Glitches or Resets.
  • Needs Firmware Development and Tight Testing.
  • Investment in all these areas, Tools and Manpower.
These made Industrial Automation with uP a challenge. CMOS digital and mixed devices and custom application devices were more easy to implement and affordable.

Analog Level by BCD Thumbwheel Switch'

The coming of Low power CMOS uC changed everything and embedded systems became smaller and robust. These were packable in DIN standard and DIN Rail Mounting enclosures.

Coming back to inputting digital data. CMOS uC and Ni-Cd Battery backed up RAM with keyboards made thumb-wheels and other methods less attractive for digital data inputs. Then the Li-Ion Battery, Flash Memory in Combination with Application Specific uC and SOC have made inputting, retaining digital data very easy and affordable.

Thursday, April 19, 2018

AC-AC-SSR Solid State Relay

This is a AC Control Input AC Output SSR Solid State Relay. When a Process Controller has an AC output or a system generates an AC signal of above 100V AC to signal the load to turn on, this device can be used. A BTA40-600 and MOC3041 are used in this.

Fire Retardant SSR Enclosures

A high voltage plastic cap limits current to a bridge which generates a small DC from 230 V AC, this drives MOC3041. The rest is the same. It is better to use a DC control SSR where possible. This AC control SSR is used where only an AC control signal is available. The BTA series has the heatsink tab insulated from the Triac chip inside. The BTB needs electrical insulation to the heatsink.

ac-ac-ssr

Electrical Control Panel Wiring

These devices BTA40600 and MOC3041 make SSR's very simple. They have proved very reliable and rugged in the field, overrate your designs, use heat sinks and seal the SSR with thermally conductive epoxy. Alumina with ciba araldite without any other filler or dye is the best way to hermitically seal.

Wednesday, April 18, 2018

555 based Reset Generator

You must have read all the circuits and explanation on the other pages at delabs to understand this, as i cannot repeat the same thing as i have done it more than once already.

The circuit is a 555 monostable, The push-switch is to trigger and generate a reset pulse for uC. The diode is for OR' ing later. The High will go thru the diode but the Low of 555 cannot drink any current as diode blocks.

555 based Reset Generator

The bottom part of the Circuit is the CD4093 Schmitt nand based flipflop. This is my favorite because of studying designs in Elektor Electronics.

What is the Schmitt then ?, It is better to visit the links below to learn. It can make a sine or triangle or any shape waveform to square. It can help square a very messy waveform.

Digital Timers Counters and Clocks

Two nand gates are connected to form a flip-flop toggle switch. When 555 gives out a pulse, the pulse is delayed by a R-C which results in a ramp, the third nand-Schmitt gives out delayed low trigger to toggle nand-flipflop-switch. The Nand-toggle-switch is rest at any time with the lower pushbutton. The fourth nand output gate is not really required. But the 4093 is quad nand, so unused nand inputs should not float , pull-up or pull-down. So it has just been added in circuit so that he can fit some role, or else he will be bored.

Monday, March 26, 2018

InfraRed LED Flasher for Optical Switch

This circuit is used to detect objects by reflected infrared light. It can be built into a cylindrical enclosure just like an inductive proximity switch.

Part of - InfraRed Detector for Proximity Switch

This is also useful as a level detector for colored liquids like oil. This has some immunity to ambient sunlight as it detects ac pulses.

Infrared Optical Proximity Switch

IC 555 is used as an astable oscillator and it flashes the Infra red LED D1 at a high speed, The object close to this LED reflects the light along with the ambient light which may also be sunlight.


InfraRed LED Flasher for Optical Switch

IR Led's and Diodes

The types available are various and polarity hard to detect even photo IR transistors can be used. The IR Led can be tested in diode mode of a DMM (battery should be in good condition) it should give around 1.1V drop in proper polarity.

Se a Related circuit here Optical Obstacle Switch.

An IR detector diode or photo diode can be tested in the same way the drop will be 0.5V at 1 feet from a 60W lamp (no sunlight), closing the IR photo diode with your hand will be an over range on DMM this will happen on proper polarity. the photo diode shows around 10k ohm resistance in daylight and in Mega ohms when covered also the photo diode detects light on reverse bias and used like that.

Tuesday, March 20, 2018

Interface a uC to PC RS232 with MAX232A

This is the standard configuration on how to Interface a uC like 8051 to PC RS232 with MAX232A. The UART or Serial port was not present in 8049/8749 chips which were the ancestors of 8051/8031. Pages of code were needed to make a software UART in MCS-48. The 8051 integrated the hardware UART and short commands made it tick. The most important innovation which made uC popular was the C in 80C31. C is for CMOS. This made the chip work cooler and work on even batteries and small power supplies.

80C51, SBC, Firmware and Circuits

The 8749 and 8751 are the UV EPROM type of uC. With limited erase/write cycles. The FLASH revolution changed every thing, you could update firmware over a phone line modem. Even without Ethernet, the firmware could be updated by making every embedded device a node on the EPABX. Now TCP/IP and Wi-Fi makes it all very easy.

Interface a uC to PC RS232 with MAX232A

PAULMON2 Hardware Requirements

The 8752 processor must be programmed with a copy of PAULMON2. The only other chip required is a MAX232, to translate the +5v signals from the 8051 to the levels used for RS-232. Of course, a +5v power supply and a standard serial cable are required.

Saturday, March 17, 2018

Amp Hour Meter using LM331 and 74C926

LM331 is a Voltage-to-Frequency Converters and  74C926 is a 4 Digit Counter. The first part of the circuit converts the amplified DC analog value from a shunt to pulses. The Second counts the pulses and Displays it on a Seven segment LED display.

Amp Hour Meter using LM331 and 74C926

In Electroplating, the time taken will determine the plating thickness which is both related to cost and quality. More current also means more metal has been used so it has to be monitored to control and deliver cost effective electro plating quality.

Mixed and Interface Circuits

A high current with low voltage is applied on special electrodes. One of the electrodes will have the job to be plated. The Medium is an Electrolyte. This is a part of Electrochemistry, Battery, Cells, Electrolytic Capacitors all belong to this branch.

Saturday, February 24, 2018

Analog mV Switch for Digital Meters

Let us assume you have to Measure Amps and Volts in four independent circuits. This becomes a Multi Channel Voltmeter and Ammeter.

Analog-Multiplexer

This circuit uses a 4052 as a DC  Analog Multiplexer, the inputs to this Mux must be from Low Impedance Output OpAmps. The Resistors Shown are not needed once the Signal Conditioning Opamps are connected. The Restors can be 100K to keep the inputs from floating, that will not load an opamp. The resistors can attenuate signals if  sensors are directly connected.

Instrumentation and Measurement Circuits

The signals from sensors have to be amplified and corrected or scaled before reaching this Switched DVM. For Current a Shunt is the Sensor and for AC current a CT or current transformer is the sensor. Voltmeter has Attenuator as the 'Sensor'.

The 7107 DPM can be replaced by the Analog Inputs of the Arduino or Microcontrooler A/D Stage.

Wednesday, February 21, 2018

Ohmmeter - Simple Resistance Measurement

Measurement of resistor values in circuit configurations are required to be made often, as these might have changed in value due to various tolerance ranges, and hence could be the cause of faults. Likewise the resistance of components used in a circuit, may need to be known. In such cases the measurement of resistance is a must.

Simple Resistance Measurement

The circuit used for measurement of voltage can be modified to measure the value of the unknown resistance. The principle followed is the measurement of voltage drop across the resistance when a constant current flows through it. In the voltage measuring circuit, the unknown resistance is connected to the same input terminals and the switch SR is operated. Then a constant d.c. current from the collector of transistor T I is passed through resistor R16 to the unknown resistance which is grounded.

MeasureAll - Test and Measuring Instrument

The voltage drop across the unknown resistor is proportional to the value of the resistance as current is maintained constant. This d.c. voltage drop is measured after proper calibration.
For the constant current source a high gain, low leakage, pnp silicon transistor (T1) is required. The range selector switch Rs, which connects the positive voltage to the constant current source enables measurement of resistances in 5 decades i.e. 200 ohms, 2 kilo-ohms, 20 kilo-ohms, 200 kilo-ohms and 2 mega-ohms.

Resistance measurement with Current Source - del20015

According to the range of resistance being measured the switch Rs also selects the decimal point of the displays in the DPM. A resistor R limits the current to the decimal point of the LED displays. Transistor T I is biased by resistor R17 and variable present VR5. As this preset sets the value of current in transistor T1, it has to be adjusted for calibrating the resistance range. Once the calibration is over, the resistance value is directly read on the DPM.

(This is scanned-ocr from my earlier file, some mistakes corrected - delabs)

Tuesday, February 13, 2018

Thermocouple and Current Input Module

This input module converts J, K Thermocouple and 4-20 mA Inputs to 0-2V Full Scale. These can be used for any voltage/current inputs too. The RTD module can be modified more easily for Voltage inputs. The control output can be On-Off or 4-20 mA/Proportional with another card. The 4-20mA I/O STC1000I is not complete in documentation.

This is a Input Signal Conditioning Card for the Temperature controller. The voltage levels from sensors are either too low or need to be translated in level and span. Then for greater accuracy some linearization methods have to be used for a more precise reading. This also increases the cost. The circuits here do no cover the linearization see others in this and my related pages.

Input Module - J and K Thermocouple with 4-20 mA

Input Module - J and K Thermocouple with 4-20 mA

The step or segment linearization can be done by transistor, diode or CMOS switches to accomplish varying attenuation/gain for stages of the curve or voltage levels. In Microcontroller systems it can be done by lookup tables or math.

In some older digital systems without a MCU, the A to D drives the address of an Eprom Array to get a Digital Data for Display, as a linearized Reading. This Corrected Data was in turn made into analog using a D/A and then on to a Chart Recorder. This was a Logic only System of the early days. Microprocessor systems was expensive, power consuming and use to frighten people by getting lost in loops or a short nap.(they have fixed that, make sure you code properly).

Monday, January 22, 2018

555 multivibrator like power oscillator

This is dual 555 multivibrator like power oscillator. This is my contraption and conception but couple of decades old. It appears to have errors. It worked but the document fixing after design worked, not done. This can be used to make a small inverter, for powering 230V gadgets of low power. The transformer is used in step-up mode. It may make a sound if the laminations are not of good quality.

This circuit can be modified using 7555 and switching transistors like BD139 driving a Ferrite 100 kHz transformer to build a Fluorescent Lamp of 10W to 20W.

555 multivibrator like power oscillator

Fluorescent lamps can be fired and lit at high frequency at relatively lower voltages. Experiment both with frequency and pulse width to get nominal lighting at good efficiency. One of the reasons CFL lamps -230V and emergency lamps 12V fail, is failure of the switching devices. These have to be overrated thrice or more, the switching heat dissipation should not be underestimated, during low/high voltage and keep a aging allowance.

Power Electronic Circuits

Designing a working circuit is no big deal. But making a batch of reliable and robust power electronics products, which are idiot proof and abuse resistant is a challenge for engineering. Then they will need it at an affordable price too.

Analog Mux for Data Acquisition Systems

Here is a 4-20 mA In/Out Analog Mux with Cascade option. This is a simple circuit i designed to make a Automation System within a budget.\

Mixed Circuits Analog with Digital

Analog Mux using 4051

This takes 4-20mA from many Transmitters and gives out just one 4-20 mA output. The Mux is done with a digital byte or word. This is a slow scanner as process is slow, that way many analog inputs can be multiplexed and sent into one analog input of a D/A. In near real time systems a faster mux could be used or mux totally avoided. This was made in some numbers, so the pcb is better than others.


Wednesday, January 17, 2018

Insulation Tester pico amplifier

With these circuits you can make an insulation tester going upto two tera ohm, hence currents will be in pico amps, great care required in design. The rotary switches for voltages and ganged interlocked range switches must not be phenolic  but  industrial epoxy based molded switches.

 The parts list which is not in the circuit, is listed below, the circuit is 15 years old. but you may get some idea on high resistance measurement. Use 1% MFR for all Resistors and low leakage plastic caps for low values. These instruments i used to calibrate with Victoreen Resitors and a Electrometer from Princeton Research, I faintly remember.

Insulation Tester pico amplifier

Theory of Operation.

The Device Under Test DUT say a transformer is placed in a Metal tray connected to the Guard SK3 terminal. The metal tray has a 3mm glass sheet on which DUT is kept. For 2 Tera ohm make sure that Humidity and Dust do not affect measurements.

Electronic Product Design

Electronic Product Design
EDA, Analog, Digital, Mixed Signal. Power, RF, Instrumentation, Interface, T&M.

Circuits by Application

Analog Circuits

  1. Battery Level Indicator
  2. Simple Sample and Hold
  3. Sample and Hold Standby
  4. Voltmeter Attenuator
  5. Precision Current Source
  6. Opamp Supply Virtual Ground

SCR and Triac

  1. Solid State Relay
  2. Normally Closed AC SSR
  3. AC-AC-SSR
  4. DC-DC SSR
  5. 2N2646 based Pulser
  6. Drive SCR thyristor

Mains Power

  1. Flashing Neon Lamp
  2. Dimmer power control
  3. Edison Bulb Life Extend
  4. Mains Current LED
  5. Mains Voltage LED

Digital Circuits

  1. Simple Digital Counter
  2. Running Lights
  3. Frequency Divider
  4. Crystal Oscillator
  5. Simple High speed switch
  6. Differential TTL converter

Measureall DMM

  1. Ohmmeter Measure Resistance
  2. Precision Digital Attenuator
  3. Precision Amplifier

Mixed Circuits

  1. Monostable Multivibrator
  2. Digital to Analog
  3. LM311 Oscillator
  4. PLL using 4046
  5. VCO with LM331
  6. BCD Thumbwheel to Analog
  7. V to F Converter ICL8038
555 Circuits
  1. OR gate with two 555
  2. fixed frequency duty cycle
  3. Pulse width modulation
  4. Astable Multivibrator
  5. uC Reset Generator
  6. LM555 Voltage Doubler
  7. 555 Power Oscillator
Discrete Circuits
  1. Isolated dual supply
  2. Sound to light converter
  3. Water operated relay
  4. Telephone Indicator
  5. Passive volume control
  6. RS232 Opto-Isolation
  7. Voltage Level Indicator
  8. Relay Driver
  9. Constant Current LED
  10. Voltage Doubler
  11. FET Current Source
Opamp Circuits
  1. Three Opamp Differential
  2. Two Opamp Differential
  3. Buffer Opamps
  4. Differential Op-Amp
  5. Inverting Opamp
  6. Non Inverting Opamp
  7. Digital gain control
  8. Square Triangle Oscillator
  9. Dual Polarity Output Amps
  10. Ammeter Precision Rectifier
  11. Voltage / Current 4-20 mA
  12. Current Source for RTD
Power Electronics
  1. Dual Power Supply
  2. Single Power Supply
  3. Battery Backup Supply
  4. 5V 1A Supply LM2575
  5. 5V Power Supply L296
  6. Dual Power Supply
  7. Tubelight Electronic Choke
  8. Voltage Doublers Multipliers
  9. White LED Lamp on Ni-Cd

uC and uP

  1. PC RS232 with MAX232A
  2. Battery Backup SRAM
  3. watchdog uC uP systems
Instrumentation Circuits
  1. Mains monitor LM3914
  2. Simple Mains monitor
  3. single digit voltmeter
  4. High Resistance Meter
  5. Diode Thermometer
  6. Function Generator
  7. Diode Leakage Tester
  8. Analog LED Ohm Meter
  9. Millivolt Source Current Loop
Process Control
  1. AD590 - temperature
  2. Thermocouple Amplifier
  3. Linearizing Thermocouple
  4. Thermocouple Amplifier
  5. 0-1V to 4-20 mA
  6. 1-5V to 4-20 mA
  7. InfraRed - Optical Switch
  8. InfraRed Detector

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