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Wednesday, September 18, 2019

Three Opamp Differential Instrumentation

This is the best Instrumentation OpAmp, Great CMRR, ensure supply has no ripple and keep analog and digital grounds separate. Ri can be replaced with a trimpot and resistor to alter gain. Connect a preset ends to pins 1 and 8 and preset wiper to VCC for Offset Null when high gains are configured.

3 Op-Amp Differential Instrumentation Amp

The Input zeners and diodes form a protective clamp for all voltages above VCC-VDD. If supply is changed to +12 -12 change zeners to 12V zeners. Use similar Zeners at output to protect Output from being zapped by overvoltages or high energy - voltage*frequency transients. Add plastic capacitors across Rf for damping AC operation or ripple. Also avoid floating inputs by providing a bias.

3 Op-Amp Differential Instrumentation Amp

There is also listed  below all the Interactive Tutorials using Virtual Electronic Components. Instrumentation Differential Amplifier using Three Op-Amps, Slide the Potentiometers and vary the mV Source, See Output DVM. This is close to the Ideal Instrumentation Amp, High Z and Excellent CMRR.

Vout = (Vp - Vn) * (2Rf+Ri)/Ri

More at Analog Op-Amp Circuits

Buffer or Unity Gain Op-Amp

If output impedance of a point is a high value then connecting another circuit at that point will load it resulting in malfunction or error. Buffers are used as interface between circuits. Low impedance of an output means it can source sink lot of current, when you need 2 opamps use LF353 or TL072 which are dual opamps.

Buffer or Unity Gain Op-Amp 

There is an Interactive Tutor in the above linked page. it has Virtual Meters and Pots, shows how a Unity Gain Buffer Operational Amplifier works. When no gain is required and you need to match impedance this can be use. Front end amps, Sensor amps. Polarity Inversion in Analog Computing or Signal Conditioning.

Buffer or Unity Gain Op-Amp

Vout = -(Vin) for inverting

Vout = Vin for non-inverting

A non-inv FET input is the best buffer, for inverting buffer use high R values Using very high R values like 2.2M or higher requires a glass epoxy PCB and guard rings around pin 2, 3 to prevent leakage currents on the PCB reaching the PINs. Also moisture and dust has to be prevented by using RTV coating or Varnish. Use 78L05 79L05 for the dual supply required by this circuit.

More at Analog Op-Amp Circuits

    Differential Amplifier - Op-Amp Circuits

    This amplifies the difference between two inputs Vp and Vn the low impedance of this configuration is a drawback, but can be used in analog computing. Optimum VCC VDD can be +12/-12. AC signals common to Vp and Vn are canceled by this configuration.

    Differential Amplifier - OpAmp Circuits

    Use a capacitor like 10nF plastic from pin 2 to 3 or across R2 to make circuit stable. For AC applications use LF351 TLO71 as they have good slew rate and also are FET inputs. For AC applications use a capacitor (1uF) in series with Ri to block DC Components. The Inputs have asymmetrical input impedance this affects CMRR, also use 1% tolerance MFR resistors for Rf and Ri.

    Differential Amplifier - Op-Amp Circuits

    Vout = (Vp - Vn) * (Rf/Ri)

    Differential Amplifier is used in Analog Computation for the Minus Operation or Subtraction. It also has a better noise rejection and CMRR, but this one amp differential circuit has low impedance as the resistors network load the signal source. It is good only for an intermediate stage

    More at Analog Op-Amp Circuits

    Monday, August 26, 2019

    Two Op-Amp Differential Amplifier

    The Input Impedance of this module is very high and is symmetric. This circuit can be used for strain gauges and for four wire measurements. If inputs are in mV use OP07. The merit is that it uses only 2 OpAmps yet has high differential Input Impedance.

    Dual Differential Amp - Interactive Simulation

    Above page has the Interactive Tutorials using Virtual Electronic Components of this example.

    Differential Amplifier using only Two Op-Amps, Interactive Tutorial Gadget. Instrumentation Amplifier. This is used in the front end of Signal Conditioners for Load, Strain and Pressure Measurement. High Z and Gain, Easy to configure Zero and Span.

    Two Op-Amp Differential Amplifier

    Vout = (Vp - Vn) * (Rf+Ri)/Ri

    The Outputs of Opamps are low impedance but still have limits they cannot drive more than a few mA of Current into the Load. If low ohmic value loads are to be applied use external transistors as amplifiers. If inputs Vn-Vp are floating Outputs may be random or Oscillating, it is good to have a bias network of 10M resistors to a potential even zero or COM this enables Vout when input floats.

    More at Analog Op-Amp Circuits

    Non-Inverting Amplifier - Op-Amp Circuits

    The input impedance of this module is very high, if U1 is OP07 it is in mega ohms, use CA3140 or LF356 fet input opamps to get 1 tera ohm input impedance, but for high gains OP07 is better as it is ultra low offset, this is a good amplifier for sensor outputs, as in a DC Circuit.

    Non-Inverting Opamp Interactive Simulation

    Non-Inverting Amplifier - Op-Amp Circuits

    Vout = Vin * (Rf + Ri) / Ri

    The zener diodes protect the opamp inputs, R1 limits current during high voltage inputs and R1 and C1 form a filter to remove ac components C1 should be a plastic type as ceramic and electrolytic caps are leaky. A large C1 will slow the response time, the sum of Ri + Rf should be greater than 5k so that output is not loaded. also do not connect output to voltages more than vcc/vdd it will blow Opamp.

    More at Analog Op-Amp Circuits

    Inverting Amplifier - Op-Amp Circuits

    Input Impedance of this module is Ri as pin 2 is at virtual ground, the opamp with feedback tries to maintain pin 2 and 3 at same potential pin 3 is at 0V hence pin 2 is at virtual ground. Clamping diodes protect OpAmp, Rf + Ri is between 5kE and 1ME as an opamp may be able to drive around say 5mA max.

    Inverting Opamp - Interactive Simulation

    Current into node pin 2 = Vin/Ri if Vin is +ve it raises potential at pin 2, in order to bring it to 0V the OpAmp sucks away the current by turning its output negative the current leaving pin 2 node is also Vin/Ri. Then Vout is given by Vin/Ri * Rf as per V=IR ohms law. Most OpAmps output swings around 1v less than VCC/VDD for full swing use CA3130 this is a FET input OpAmp, and has low bias currents in pico amps.
    Inverting Amplifier - Op-Amp Circuits

    Vout = Vin * (-1) * (Rf/Ri)

    This is used as a small signal amplifier. Used after the buffer stage. Multiple stages cascaded for higher gains. An Interactive Tutorial with Simulated Meters and Potentiometers, demonstrating how an Inverting Operational Amplifier functions in page below.

    More at Analog Op-Amp Circuits

    Friday, July 26, 2019

    Universal Signal Conditioning Circuit

    Here is a practical application of the dual differential amp. This circuit is for DC or slow moving DC like Strain Gauge and transducer signals.

    The RC and Zeners are for protection and clamping. Why and how has been described in other posts here. The high impedance op-amp input cannot face the real world unprotected.

    Universal Signal Conditioning Circuit

    OP07 is always the selection due to the low offset. When the sensor generates data in mV, you cannot afford any error introduced in this front end, right. Here OP290 is used for better performance. This dual opamp is better for building a two wire 4-20mA transmitter. But Op07 is fine for a three wire transmitter which consumes more power.

    Observe the Power supply decoupling caps, this is a rule and every chip needs a power cushion. The front end zeners and caps have to be low leakage in many applications, ensure you have such parts or test them.

    Opamp Instrumentation Circuits

    There are two trimpots, bourns multiturn PCB trimpots. One for Offsett-Null or Zero and other for Span or Gain. You have to tweak them in a alternating sequence as they are interdependent to some extent.

    Now your weak transducer with a voice in mV and uV; can meet an A/D "Eye to Eye" and let the whole world know what is the Weight, Temperature, Humidity, Pressure or Moisture Content in the Harsh Real World full of uncertainties.

    Thursday, July 25, 2019

    Linearizing Circuit with Opamps

    The thermocouples and some other sensors have an output that is non-linear. That means the mV generated by them are not in direct proportion to the parameter measured. In signal conditioning Linearization can be done with cmos fet switches or even comparators and diodes.

    Linearizing Circuit with Opamps

    In Embedded Systems Linearization is done with Look-Up tables on ROM and also using Math and Formulae for each segment.

    The above circuit used diodes and opamps to change the gain for each segment of the curve to make it a straight line within an acuuracy of 1% or 2 %.

    LM346 has programmable gain and 4 opamps in one package. The LF442 is a dual low power operational amplifier and superior for DC application in comparison  to LM358.

    The about configuration increases or decreases the gain of the block. You can use each opamp and the dip-switch to change the gain. The resistor selection is important for obtaining the right gain.

    Wednesday, July 24, 2019

    Auto ranging 4-1/2 Digit Digital Voltmeter

    Auto Ranging for ICL7107 had to be done with window comparators. In ICL7135 Digital Outputs are available for autoranging. Here in this circuit is a close approximation of what i may have designed once.

    Auto ranging 4-1/2 Digit Digital Voltmeter

    The below Details from Datasheet - These pins are used in this circuit to Autorange the DPM with some peripheral CMOS Logic.

    Auto ranging 4-1/2 Digit Digital Voltmeter

    "OVERRANGE (Pin 27) - This pin goes positive when the input signal exceeds the range (20,000) of the converter. The output F/F is set at the end of BUSY and is reset to zero at the beginning of reference integrate in the next measurement cycle.

    UNDERRANGE (Pin 28) - This pin goes positive when the reading is 9% of range or less. The output F/F is set at the end of BUSY (if the new reading is 1800 or less) and is reset at the beginning of signal integrate of the next reading."

    ICL7135 4 and Half A to D converter with BCD Output

    The Range is Defined by QB and QC of 4029, there are four ranges. The two bit Code from this can control the decadic range of an Attenuator or Amplifier.

    The Overrange and Underrange are in a OR formation with R26-27. Clock from either will Inc/Dec 4029. The Underrange Pulses are used by D2 -C8 to form a Steady Logic signal on Up/Down Control of 4029. This works in a closed loop manner, to Change the Range to match input Signal. When there are no Pulses from Either UR or OR, then that range is held.

    Friday, June 28, 2019

    16 Channel Analog Multiplexer

    This circuit is built around the chip CD4067, now called 74HC4067, it works like a single pole 16 throw rotary switch that can be controlled digitally. Clamping protection diodes are built in. Use resistors to enable this protection.

    16 Channel Analog Multiplexer

    Pan and Zoom the Circuit for detailed Study here - Sixteen Channel Multiplexer

    The ON Resistance of this chip is around 100 ohms and OFF resistance may be in Giga ohms. Use  74HC4067 for CMOS periphery. 74HCT4067 for a TTL environment.

    16 Analog channels are controlled by a Digital User Interface circuit made of 4093 and 4029. Up/Down and Auto/Man are four Push-buttons. A LED Display to show the Channel Number that is selected.

    Mixed and Interface Circuits

    The output of the Mux goes to OP07 whose high input impedance and low offset enables an accurate low impedance output that can go to the A/D Convertor, PLC Unit or DPM - Digital Panel Meter or voltmeter.

    Wednesday, June 26, 2019

    Synchronized Sample and Hold Analog Mux

    This circuit has two analog mux 4051 operating in synchrony to store an analog value in a low leakage tantalum capacitor. This makes an Analog Memory possible and overall system accuracy of around 2%, which was more than adequate for this process.

    Mixed Circuits Analog with Digital

    The analog value from a temperature transmitter is available for a short duration when it is collected from a rotating system with copper brushes and contacts on the shaft.

    Synchronized Sample and Hold Analog Mux

    Pan and Zoom the Circuit for detailed Study here - Synchronized Analog Mux 

    The CA3140 with one tera ohm input impedance ensures the accuracy of the analog memory. The scanning by 4029 counter frequently refreshes and updates the analog data.

    The 4-20mA signals are converted to voltage by a 50 ohm shunt 1% MFR of 1Watt rating. The clock and reset signals are coming from 12V proximity switches. This is filtered and tamed by a simple transistor circuit. That way the 5V Logic circuit is safe from the 12V external inputs.

    Since both the 4051 operate in tandem the analog value in the tantalum capacitor does not discharge through the 50 ohm shunt current receiver.  The CMOS switches offer very high OFF resistance, that makes this circuit workable if properly adapted.

    Digital Control for 8 Channel Analog Mux

    A single Voltmeter or Digital Panel Meter DPM can monitor 8 Analog inputs from sensors or potentiometers using a Mux chip and creating simple digital controls for that.

    The Pushbutton Logically Interlocked Controls are Auto and Manual. For Manual Setting Up and Down push-buttons select the channel. In the Auto mode the 4029 counter gets pulses from a 4093 Schmitt Nand Gate wired as an Oscillator. This circuit shown for six channels.

    Industrial Process Control Circuits

    Four pushbuttons on the front panel control the scanner.  One 4051 is used to multiplex 8 trimpots that hold the Analog Alarm Settings. The channel number in BCD is  translated to a LED channel Display with a 4511 chip.

    Digital Control for 8 Channel Analog Mux

    Pan and Zoom the Circuit for detailed Study here - Digital Control for Mux

    The 6 or 8 LEDs decoded by the 4017 are placed just above each Trimpot. Select the channel and tweak the trimpot of the LED that is turned on. The output of U7 OP07 can be measured with a digital voltmeter to monitor the trimpot setting value.

    Digital Timers, Counters and Clocks

    This way all the channel alarm settings can be trimmed or tweaked by watching the voltmeter while turning it. Carbon or metal film presets should not be used for this. Something like Bourns ten turn trimpot. If changes made are more than ten times a month, you would rather use a bourns ten turn potentiometer.

    Monday, May 27, 2019

    LM331 A to D with Mux Input Switch

    This is the full circuit of a V/F convertor interface for 80C31 SBC. The Mux is configured for selecting between two inputs. It uses analog switch 4066. LF353 along with LM331 form the VCO, you can further study such configuration in the Application Notes of TI/NS.

    LM331 A to D with Mux Input Switch

    This design is built above an application note.  Two Pt-100 RTDs are switched to the A/D using the FET Switches.  Here a 1mA Precision current source is shown at the bottom for RTD and a 50mA Current source is shown above for special uses as an example.

    Mixed Circuits Analog with Digital

    The Output Fout is a Frequency which is directly proportional to the measured voltage Vin. The pulses can be isolated using opto-couplers to avoid ground loops or electric hazard. An additional protection and scaling circuit at the input may be required for some sensors.

    delabs designs - delabs notes

    Sunday, May 26, 2019

    Tacho Counter usong ICL8038

    This circuit is alternative approach to same solution show in earlier post. Here i have put the complete circuit in PNG format. 8038 is a marvelous chip, a custom monolithic analog computation unit, a device popular around the 80s, it was far ahead of its times indeed.

    Now its availability and application are much reduced. Intersil made Popular Analog ASICs, the word ASIC itself came much later. They were also early in making low power cmos, this was at a period when microprocessor system consumed a lot of power and microcontrollers had just started coming in.

    Tacho Counter for Speed and Quantity Measurement

    This was a small circuit made for driving an Impact counter. The heart being ICL8038. It must have been a Motor driving a Conveyor, the motor has a feedback attachment called Tachogenerator.

    Tacho Counter usong ICL8038

    Only part of the circuit is shown here. See the image of product here Tacho Counter. The configuration is derived from the Application Notes of Intersil. The Voltage from Tachogenerator is Measured on a DPM-DVM and also fed to this circuit after attenuation and filtering.

    Function Generator using ICL8038.

    The square pulses of 8038 is used to derive a Logic pulse train for a CD4040. The CD4040 works of 0 and 12V. The above circuit is on +12 and -12. That is the reason R10-R15-Q1 are used. The pulses are 0-12V pulses. The Zero is Virtual like the Virtual Ground in low current power supplies.

     delabs designs - delabs notes

    Friday, May 24, 2019

    Tacho Generator - VCO using Opamps

    The opamp section of VCO was published earlier for better readability. The full Orcad Schematic in PNG format is here. Many an instance, analog solutions are not only cost effective but very reliable if properly manufactured. They are also as Real-Time as real time can be. Hence never give up on analog for small solutions. It can never be substituted in the front end where the device has close encounters with Real World Parameters.

    Even if you have a miniature IoT device, there is a analog front end to it and it gets integrated into the chip too. The designers should always understand how to ensure that the analog front end is robust by using proper protection, filtering or isolation when necessary.

    Tacho Counter for Speed and Quantity Measurement

    The pulses can be used to advance digital counter or mechanical counter using a solenoid driver transistor circuit. The Voltage Vin can be further scaled and fed to a Digital Panel meter to read the rate.


    This is a Voltage to pulse converter using opamps for measuring speed or rate from a Tacho Motor mechanical coupled to a Conveyor System.

    See the complete circuit in my site to study other sections. The motor DC out is filtered and scaled. Then the clean safe dc is fed to this VCO based on a generic application note design. 

    VCO - Voltage Controlled Oscillator using Opamps. LM339 is a quad  Comparator.

    The complete PDF circuit and other such circuits at my Mixed Circuits Analog with Digital

    delabs designs - delabs notes

    Tuesday, April 30, 2019

    Fluid or Water Level Indicator

    The Reed Relay based Float Switches are used in Automobiles and even corrosive and volatile fluids. This can also be used to indicate level of water or operate pumps.

    The reeds are hermetically sealed in glass, Like the Incandescent bulb. The signal switched by reed also should be a few mA or even uA. This makes is safe in Volatile fluids, where sparking can cause fires.

    Fluid or Water Level Indicator

    This is a way by which you can monitor the level of fluids like water in a tank. Based on data from the sensor you can control things like solenoids or motors as required or even turn on a buzzer, hooter or annunciator in a control panel.

    Water Level Indicator with Reed Relays

    Then you need to assemble a small circuit within the long plastic pipe. Many reed relays with a chain of resistors in series has to be inserted in the pipe. The resistor and the glass reed relays should be in different levels of the pipe where you need an alarm or indication. Seal the pipe hermetically at both ends with epoxy resin after taking out a shielded cable of just 2 wires + 1 ground shield.

    Monday, April 15, 2019

    Analog to Digital with a V-F LM331

    A Low cost A/D with a Potential of 5KV Isolation from Computing elements by use of Normal/Special Opto-Couplers. This can give better resolution and accuracy than a 8 bit A/D. may be close to 10 bit A/D. Added advantage is that you can optically isolate the inputs.

    Analog to Digital with a V-F LM331

    Suppose your temperature sensor touches a heating element OR your speed sensor is subjected to a shock from a defective motor with earth line broken. Such situations happen in the field, even at home or lab. Sometimes it is carelessness, other times it is wear-tear. Many times it is breakdowns, accidents etc. So do not let the High voltage to get at your Microcontroller Board.

    More about Embedded Micro here - Hyper Embedded

    Monday, April 01, 2019

    Regulated Power Supply 24V with 2A

    Here is a simple to build regulated power supply. The two diodes are to boost the 24V to 25V DC. It uses regulator 7824 and TIP2955 PNP Transistor to boost current.

    24V and 25V Power Supply with 2A Current

    1. choose a transformer with a close match of what is available.

    2."100V 3A" at the bridge is the minimum diode rating also(or use 4 x 1N5408). "100V 3A" is also minimum bridge rating use a close match.

    3.to make a bridge with 4 diodes refer my other circuits, there are many.

    4. 22V AC leads to around 30V unrectified DC which is good, if the 30V becomes more, the heatsink needs to be very big.

    5. the ground of regulator is lifted by (0.7*2) by 2 diodes to provide 1 V above 24V, as 25V regulator does not exist. the power supply 'neg' can be grounded or earthed,

    6. the supply is a+25 V from ground or negative, but things are only relative.

    7.if you need a dual supply 3 terminal , that is ground +25 and -25 then for -25 one more circuit using 7924 and tip3055(npn) has to be made.

    8. use any high current pnp transistor (5A) you have put a heatsink with heatsink compound.

    delabs

    Tuesday, February 26, 2019

    Controlled Oven for stable Reference

    This is a continuation of the previous two circuits. This circuit controls the temperature in a miniature oven that holds a stable dual voltage reference.

    Controlled Oven for stable Reference

    In colder seasons or locations this will maintain the temperature at a higher level. A mini fan in the equipment ensures external heat does not reach the oven, fan keeps the larger chassis cool.

    Temperature Measurement and Control

    This circuit may fail if the equipment is in very hot open locations, big heaters, hot machines or direct sunlight falls on equipment OR the Lab is not cooled to near normal ambient temperatures.

    High Stability Reference Mirror

    LM399 is a Precision Reference chip. From this a dual polarity mirrored reference is derived using OP07 op-amps. This assembly is mounted in a miniature oven to ensure temperature stability. 

    High Stability Reference Mirror

    The oven used Two Steel Boxes one mounted in another with Glass Wool In-between to reduce heater losses.  Steel was used to ensure excellent EMI-RFI Shielding. Both the outer and internal shell was earthed.

    Instrumentation and Measurement Circuits

    Regulated and Filtered Supply to this assembly further ensures consistent performance over the years and in various environments and seasons.

    Sunday, February 24, 2019

    Differential amplifier for HV Power Supply

    This is part of a precision High Voltage but Low current Power Supply for Testing leakage currents in passive devices. This Supply is a module for a  Automatic Test system in component inspection.

    Differential amplifier for HV Power Supply

    HV Precision Power Supply Circuits

    Insulation of Transformers and the Isolation of plastic capacitors are best analyzed by applying a High Voltage and measuring the leakage currents.

    These currents are in the order of nano-amps and pico-amps; values close to the bias-currents and leakage currents of devices. Some offsets and corrections can be done in software for the ATE systems.

    Monday, January 28, 2019

    SSR Solid State Relay DC Control

    This is the newer version of NO - Normally Open DC Control SSR. It has a Constant current source that is more stable and robust.

    You could use it to control AC powered Electricals like Heaters, Motors and Fans. It can also be used to Switch ON and OFF any Equipment, Control Panel or System.

    SSR Solid State Relay NO New

    You have to choose the correct current rating and heatsink needs of Triac. This is the older version below. It has a shunt current control. This new circuit above has a regulated current source.

    DC-AC Solid State Relay or SSR - del30008

    This is a basic output Module in control systems. It is faster than Electromagnetic relays but has some heating in the triac. Some designs with mosfets are also available. SSR with a IGBT - Insulated Gate Bipolar Transistors also can be made for large powers.

    Thursday, January 24, 2019

    Generic LM317 Switching Supply

    This was a common way LM317 was used to get a stable power for small devices. It is still useful for learning and some blocks of the circuit are still used today in modern industrial systems.

    Generic LM317 Switching Supply

    Before the SMPS took over as the default DC source in most systems; designers would use switchers to reduce thermal losses in Linear Supplies.

    Linear Supplies have practically no noise or EMI_RFI (generation) issues . It is clean but not green. The efficiency is low. Transformer loss, heat loss in devices. The Product Safety is very high; but you need to use a Toroidal or Split-Bobbin Transformer for better isolation.

    Power Electronic Circuits

    The cost of these supplies are high as more copper is used, the space and weight is also considerable. Reliability and long term stability is excellent in these systems.

    Dual Supply +5 and -5 using 555

    In this circuit the 12 DC, two wire is converted to three wire +5 and 0 and -5 dual supply useful for op-amps or other interface circuits. You could use 7805 and 7905 low current TO92 package.

    Dual Supply +5 and -5 using 555

    Regulated supply is essential for precision analog circuits.  This also could be used for signal conditioners that are built into the sensors. They are called voltage or current transmitters.

    Negative supply also ensures total off or high-z in cmos analog switching. If you have crosstalk or leakage error in the Analog Mux; use a dual supply FET switches to turn total off and total on.

    Instrumentation and Measurement Circuits

    Datel (ge) mux chips had low on and off, but were expensive. Some cmos switches can improve with dual supply, but care to be taken that the negative voltage does not reach the ADC or uC stages.