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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.