Electronic Designs, Digital, Analog, Power and Electrical Circuits.
Schematics of delabs

Friday, December 28, 2018
Test Circuit for Logic Analyzer software
The speed at which the logic state changes say like 10 M Hz while probing even a PIC or 89C51, is too fast for this circuit. For that, the incoming data has to be spooled or stored in RAM at real time, by the external Hardware itself.
Test Circuit for Logic Analyzer software - del20006
As this is a Parallel Port Interface, an Embedded High Speed Digital RAM Storage of Multiple Logic input Channels with Signal Conditioning in the front end, could do the job. This is the minimum, if you want to program the rest of the instrument on Computer Software.
Thursday, December 27, 2018
Simple Printer Port Interface
So i made some example circuits and VB programs for students. A demo Milli Volt source, Digital Voltmeter and Logic Analyzer examples for learning, are on these pages. I have tried to derive power from PC itself in this circuit, Care should be taken not to short circuit or apply any voltages above 5V to PC Port Pins
There are protection in all chips these days, but you may stress the limits, so design and use opto couplers to be on the safer side.
Simple Printer Port Interface
74HCT373 is the only chip used to interface the real world with the PC Parallel port. The Inputs to this chip are protected with Resistors and Zeners. 3 outputs of PC are also monitored using LEDs. This gives you a IO interface for experimenting. Below is a Preset counter simulation that you can use with this circuit for testing. Schmitt Triggers and Signal Conditioning may be required for Noisy and Non-Sandard Inputs.
Wednesday, December 26, 2018
Milli Volt Source for Printer Port
This circuit is a R-2R, Digital to Analog Converter. You can replace the R2R with a D-A Chip for better performance. This circuit is just to understand the Concept, for learning and Experimenting.
The MFR resistors are 1%, hence the precision of this Conversion is not very good. It is ok for servo applications or closed loop conversion along with the ICL7135. That can be tried with software.
Milli Volt Source for Printer Port - del20004
The eight outputs from printer port are latched to U1 and U2 by controlling U3B using software. Place data at output then instruct U3B to latch the data. Then we have a digital byte at output of U1-U2 which is set by software. This is converted to analog with a R-2R Resistor Ladder DAC. U4 buffers the Ladder output and U6 gives a Negative polarity output of same analog value.
Thursday, November 29, 2018
Millivolt Source with Digital Potentiometer

Description. - In this Circuit, digital potentiometer, connect pushbutton switches to fast and slow with one end to +7.5V, when you hold the button down the analog voltage will ramp up-down, fast or slow, this will enable you to make a digitally controlled millivolt source or power supply.
Digital Potentiometer - del50003
Here is a Millivolt Source i built for Calibration in the early days. It uses only CMOS Digital and Mixed Chips from Intersil and CD40xx Series.
Wednesday, November 28, 2018
Optical obstacle switch with LM567

Description - The 555 monostable has a 1 second period, If pin 2 gets low trigger pulses of a frequency more than 1 Hz, the output pin 3 will remain high, if the trigger pulses came in 10 second delays then output will go on and off, so also the relay and the electrical load on relay contacts. Like an integrator, it will not operate relay very fast. Even in a fridge stabilizer they put something like this else the compressor motor is damaged on frequent black-brown outs.
Optical obstacle switch - del50006
Now for the LM567 part, The clock at pin 5 flashes the IR Transmitter LED LD1 at a frequency set by C7-R5. The IR Photo Sensitive Diode or Transistor LD2 conducts when light is got from the IR LED. As the lights is in pulses, so also the impedance of LD2 goes low and high at same frequency. This develops an AC waveform across R3 over a DC representing Ambient light.
Tuesday, November 27, 2018
Solid-State Stabilizer Step up 110V AC
It also uses the LM324 quad opamp from National Semiconductor which is low power and single supply. As the MOC3041 switches the Triac at zero crossover there is no inter-winding short of transformer on crossover hopefully, the control circuit is designed in such a way that more than one triac will not be turned on at a time, i would like you to give feedback.
Solid-State Stabilizer Step up 110V AC
The triac will switch at zero cross over because of MOC3041, hence no problem of an interwinding short, but then control circuit may fail or malfunction, so use fuse as shown . Also a snubber made of a 47E resistor and 0.02uF 630V pl cap in series must be placed across each triac.
Use heatsinks for all parts that heat, air circulation. Use Presets with series resistor as required so that you can test or calibrate. This Stabilizer should not be used with Inductive loads like motors or solenoids it may be ok for lighting and small electronics.
Tuesday, October 30, 2018
Stabilizer Step up 110V AC to 230V AC 500VA
There is an overload, under voltage and over voltage trip circuit.U2A and U2B are two comparators which controls relays K2 and K3 Respectively. One Boosts the voltage (Step-up) when mains supply is low. The other Bucks the voltage (Step-down) when mains voltage goes beyond a limit.
Stabilizer Step up 230V AC 500VA
U2C and U2D work like a window comparator to trip the unit above and below certain preset limits. This circuit is clubbed with a Mains control relay K1 which can be Turned ON-OFF with two pushbuttons.Put a 0.1uF 1KV pl cap across all relay contacts to avoid sparking.
Relay current paths should be large and direct to supply, or when relay operates ground will lift and cause malfunction.All mains wiring and connections should be designed for high voltage and current, They should be isolated visually from control circuits by 10 mm or more. If input voltage is 230V put the two 110V windings in series in proper polarity
Thursday, October 25, 2018
Mini RTD Pt-100 Transmitter
The customer wanted a two wire system, this needs low power opamps which were ten times the price. If this transmitter works at 3mA it could have been two wire. Those parts were in short supply and the budget of customer was low. So i made it with regular opamps but three wire. The customer was satisfied as he got a cost effective solution. But now the situation of markets and products are different.
RTD Three Wire Transmitter
These are the circuits and boards of a Mini Temperature Transmitter for a Platinum hundred ohms temperature Sensor. Has a 4-20mA sink output. Current Loop can be used for multiple instruments.
ICL7135 is a simple solution. It has a serial output that can be used to Drive IR Leds. Remotely sense these flashes in a Micro-controller and you have a reading. You may be able to use optic-fibers too. Where volatile liquids are present so that the risks of sparks can be eliminated.
Friday, October 05, 2018
RTD 3-W Mains Power 4-20 mA Transmitter
We can classify Transmitters as shown below. The Measured Parameter Temperature, Flow or Events Has to reach an Intelligent Data Storage and Analysis System. It may just be an Human Operator who jots the data on a Notepad and Turns a Few Dials based on his Experience or an embedded controller. It could even be a Computer Network or a Web Application used,
RTD PT100 Transmitter and Multiplexer PCB
- Analog Transmitters - Like 4-20mA Loop.
- Electrically Isolated Analog Transmitters.
- Transmitters that need to be Intrinsically Safe.
- Digital Transmitters and Optical Interface.
- Wireless Transmitters and TCP-IP.
Process Control Instruments and Custom Solutions has been my core Strength. The RTD Pt-100 Transmitter with 4-20 mA output shown here was used in numbers with a 4-20 mA Analog Multiplexer. This was in turn monitored/controlled by a PLC SCADA System to monitor many points in a large Industrial Plant. The external multiplexer makes unlimited channels possible with a Standard Analog Input and Digital Output Module.
Friday, July 27, 2018
Voltmeter Attenuator Rectifier
Voltage measurement attenuator amp

Specifications :-
D.C. Voltage
Ranges : +/- 200 mV, 2V, 20V, 200V, 2000V.
Input impedance: 10 mega ohms.
Circuit protection: + 2000V D.C. all ranges.
Over range: 100% to 1999.
Accuracy: +/- 0.5%.
A.C. Voltage
Note: Average responding Ranges calibrated for sine wave.
Ranges: 200 mV, 2V, 200V, 2000V
Input impedance 10 mega ohms.
Circuit protection : 750V r.m.s., all ranges.
Over range: 100% to 1999.
Description :-
As our DPM is capable of measuring only 200 mv full scale deflection, the input voltage in the case of exceeding the range needs scaling down. This is achieved by an attenuator chain.
Wednesday, July 18, 2018
Ammeter and Precision Rectifier
Current Shunt Amplifier digital control
It is found convenient to measure current rather than voltage for knowing power output and determining efficiency. It may be required to measure leakages in circuits at certain times. Hence the measurement of current constitutes a priority.

Measurement of DC Current -
The circuit diagram for the measurement of current (d.c. and a.c. modes) is shown aside. For measurement of current switch SI is operated. The switch S-ad is kept in d.c. mode. This enables the current to pass through a shunt circuit consisting of resistors R26, R27, R28, R29 and R 30. The current ranges are provided in 5 decades i.e. 200 micro-amps, 2 milli-amps, 20 milli-amps, 200 milli-amps and 2 amps. An additional current range that can be read upto 20 Amps is also provided. However, for measuring this high current the green terminal provided on the meter should be used. When a current to be measured is fed to the input terminals of the instrument appropriately, a voltage proportional to the current through the shunt resistor is fed into the DPM which measures the d.c. voltage which in turn indicates the d.c. current being fed.
Test and Measurement Instruments
Measurement of AC Current -
In case of a.c. measurement, the switch S-ad is kept in a.c. mode. The a.c. current path is similar to the d.c. current path in the shunt resistor. However the voltage tapped across the shunt resistor is fed into IC2 which is a buffer. The output of IC2 is fed to IC3 through capacitors C10 and C11. This IC is an operational amplifier acting as a precision rectifier. The output of IC3 is fed to the input of the DPM for measuring the a.c. current being fed to the input terminals. It can be seen that the current measurement is similar to the voltage measurement except that the attenuator chain is replaced by the shunt resistor circuit.
(This is scanned-ocr from my earlier file, some mistakes corrected - delabs)
Friday, July 13, 2018
Multi Output Instrument Power Supply
List Of Components For Power Supply.
1. Transformers - X1-6-0-6 (500 ma), X2-12-0-12 (500ma)
2. Semiconductors - IC6-7805, IC7-7808, IC8-7908, D1 to D10-IN4007, D11 and D12 - 12v, 1W, Zener
3. Resistors. - R1 and R2 - 100E 1/2 W CFR
4. Capacitors. - C 40v , C5 and C8 - 1000 Mfd , C1 - 2200 Mfd, C5 and C7 - 0.1 Mfd, C9 to C12 - 100Mfd
5. Miscellaneous - F1-250ma, N1-Neon, 3-Pin Mains Chord.

POWER SUPPLIES:
The required D.C. power supply is usually obtained by means of a transformer. It is also possible to have transformerless power supplies. Though the elimination of the transformer makes the circuit compact, economical and simple, also facilitating quick assembly and built in short circuit protection, certain drawbacks creep in. These power supplies are useful only for low current applications.
Special safety precautions ? are to be followed while using them. Physical contact should be strictly avoided, since the output terminals are not isolated from A.C. mains supply.
Workbench Power Supply
This obviously necessitates the use of a transformer. By suitable modification it is possible to obtain multiple/ fractional dual voltages from a transformer. Different not-so obvious voltage values can also be obtained from the transformer by rectification circuits. The output so obtained from a transformer secondary is unregulated. For good load regulation, the internal impedance of any power supply should be as low as possible. The regulation can be improved either by resistor zener method or series regulator method.
Monday, June 25, 2018
Constant Current Source LED Drive
LED Voltage Level Indicator
BC547 is like 100mA-40V-200b, Limit collector current to 60mA, use it at less than 25V and depending on the individual transistor you may get a DC current amplification of 200 times. That is 1uA of base-emitter current could give a whooping 200uA of collector-emitter current.

Still Thinking we do not have the Lower-NPN we calculate the resistor. Vcc - ( 2 LEDs * 1.7) - Vce = Vr that is the voltage across the resistor. You know ohms law and the current needs to be 15mA for a bright and long lasting LED. Lastly 1.7 the forward drop of a green LED and 0.6 a saturated or Turrned-On NPN Vce.
Mains Voltage Current LED Indicators
Now you use the Lower-NPN, The above calculations do not hold anymore. Let us think a small current is flowing in the LED. Then the voltage across R is less than 0.7V, that means base-emitter diode of the Lower-NPN will not get to conduct. The Collector does not draw any current away. Now think that more current flows in LED, the voltage across R builds up above 0.7V the Lower-NPN is biased. The collector of Lower-NPN starts drinking current from the base of the Upper-NPN. So The Upper-NPN starts losing its bias. This lowers the LED current and contains, regulates or controls the LED current as shown in the formula.
Saturday, June 23, 2018
High Resistance LED Meter
High Resistance Insulation Materials
A negative voltage is derived by shifting gnd with two diodes, i feel this did not work very well. Two pins of CD4028 pins are also used to boost the reference to get two extra ranges as 4051 has a 100E on resistance.

The 555 clock makes 4029 counter count. But the clock can be clamped to gnd by a TL062 window comparator. The clock is frozen when the input value to comparator pin 5-2 is within a lower limit and upper limit "window" pin 3-6.
Insulation Tester
The 4029 counter BCD is decoded to decimal by 4028 which drives the LEDs, keep LED drive within 3mA or chip will be loaded. Use high efficiency extra-bright LEDs.
The 4029 BCD also controls a shunt resistor array with CMOS switches 4051. The voltage across shunt is a sample of leakage current. This is compared in the window comparator to freeze the Clock and LED display to give a reading of the leakage current or Insulation Resistance.
Friday, June 15, 2018
2N2646 based Voltage controlled SCR Pulser
2N2646 is a unijunction transistor(UJT) in a TO-18 metal package. The control voltage or voltage proportional to error is fed to R56-Q3, The UJT drives a pulse transformer which provides isolation from the Load which the SCR bridge is controlling.

This phase angle control gives a near Linear closed loop control for a SCR bridge which may be used in Electroplating or a Preregulator of a big power supply.
High Energy Circuits
MOSFET and IGBT based systems are now more in use than Thyristor - Triac - SCR based designs in power electronics. Thyristors are more robust than many power devices.
Friday, May 18, 2018
Precision Amplifier with Digital uC Control

This circuit DACT0009 is similar to DACT0008 but gains of upto 100 can be realized in this configuration, this is useful for signal conditioning of low mV outputs of transducers. The gain selection resistors R3 to R6 can be selected by the user and can be anywhere from 1K to 1M and can also be trimpots for obtaining gains as required by user, the resistor values shown are for decade gains e.g. for an auto ranging DPM.
Precision Amplifier with Digital Control
R1 and C1 reduce ripple in input and also snubs transients, ZD1 and ZD2 Zeners clamp input to +/- 4.7V the input current is limited by R1 lastly C1 and C2 are decoupling capacitors. The OpAmp U3 is used to increase the input impedance so that very low mV inputs are not loaded on measurement, the user can terminate the inputs with a resistor of his choice like 10M or 1M to avoid floating of the inputs when no measurement is being made.
Thursday, May 17, 2018
InfraRed Detector for Proximity Switch
Circuit Operation
Part of - InfraRed LED Flasher for Optical Switch
The infra red diode D2 detector gets the reflected light from LED and some ambient light, The forward voltage drop of D2 will vary with the amount of light falling on it. Ambient light causes a DC component and the pulsing light from D1 causes an AC component.

The capacitor C6 blocks DC and only transfers AC pulses if any to opamp amplifier U3A whose gain is set by R18, D9 rectifies the pulses to DC and this DC voltage is used by opamp comparator U3B which drives Q1 through Q2 for an open collector output for relays. LED D7 turns on when relay Output is high.
R14 and R13 can be replaced with potentiometer for threshold adjustment if required.
Testing
Connect 12v DC supply to +V and GND Ports, Connect a relay coil Between OUT and GND Ports, you can use the relay contacts as you require to turn on a lamp, heater, fan or motor.
If all connections are ok and ICs are working you should see a +5V at U3 pin8 VCC and around -4 to -5 at U3 pin4 VDD.
See also - Mixed and Interface Circuits

Construction
The Optic switch can be used for both reflecting detection (retro reflective) or obstacle detection. The mechanical construction will decide this, for obstacle detection the diodes D1 and D2 could be put in two different tubes and can be kept far apart 2mts+ and both should be exactly opposite each other, any obstacle like a passing person will be detected.
To make a retro reflective proximity switch this circuit is ideal, it can be housed in a cylindrical 30mm by 70mm metal unit with m30 threads and nuts for mounting, both D1 and D2 have to be fitted in the front of this tube on a plastic plug optically insulated from each other yet beside each other.
Tuesday, May 15, 2018
Voltage Doubler with Diodes

If you feed a Low Impedance Square wave, like output of 555, which has adequate Source-Sink Punch. to Input A, then it is quite possible you get double the voltage at B on No load.
Mains Voltage Current LED Indicators
There are many designs you can do with just resistors, capacitors, diodes and LEDs. Zeners and Inductors will add to the fun. The Transistor or Zener can make the circuit smart.
Friday, April 20, 2018
Analog Level by BCD Thumbwheel Switch
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.

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
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.

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
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.

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.
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.
This was built for a Varnish Impregnation Unit. It could be Epoxy or
some liquid used in Coil-Capacitor Vacuum Impregnation Process.
This
was fixed behind a Glass Window, when the liquid reaches this level,
the circuit senses it and works like a limit detector. Hence the name
Optical Proximity Switch. It is fairy simple in design. It worked after a
few trials.
This was a custom design. We always should cost
custom designs more, there is more time and materials used up. Only when
some quantities are made, you can make it break even.
Costing
should also involve a R&D component, this is needed to build the
in-house lab. Many good firms today, owe their present performance to
the research effort and investment done by their predecessors.
Tuesday, March 20, 2018
Interface a uC to PC RS232 with MAX232A
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.

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.
Friday, March 16, 2018
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.
Friday, February 23, 2018
Analog mV Switch for Digital Meters
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

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 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
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 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.
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
Mixed Circuits Analog with Digital

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
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.
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.