delabs Circuits

Thursday, April 20, 2017

Insulation Tester power supply

With these circuits you can make an insulation tester going upto one tera ohm (2 Tera ohm max). hence currents will be in pico amps, great care required in design. Also 1000 Volts DC is generated which can cause injury. take great care. the above circuit is for the advanced instrumentation hobbyist only, do not try it at home.

Insulation Tester or Teraohm Meter with Polarization Index 

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.

IC7, IC9 - NE555 - Timer IC
IC8 - LM723 - Voltage Regulator

The above list is from my memory, hence it may be wrong, i have forgotten this circuit, this circuit was scanned by a hp photosmart and resized and optimized by irfanview. also note the technology may be obsolete, but basic idea is still the same today.

Insulation Tester power supply

Theory of Operation.

 IC7 555 as an Astable chops the DC with T2 NPN transistor. TR2 was a Russian U Core High-Freq Transformer. The secondary was insulated with mylar, layer to layer and impregnated in Mica-Lacquer or varnish. The 723  Chip along with T1 is The closed loop regulator which changes the DC which is chopped.

The high voltage is attenuated and that is the feedback to 723 chip which by comparing to a reference, controls the output. The diodes and caps are in series to withstand 1000V and above.

Sunday, April 09, 2017

Opamp Supply on Buffered Virtual Ground

When a Inverting Opamp Configuration is at a steady state, we say the Inverting Input is at a Virtual Ground. That means it is at 0V w.r.t to the dual power supply ground, but it cannot drive or draw any current. It is at a high impedance, but still at 0V. When you buffer this 0 V, you get a low signal ground for a opamp supply.

Analog Buffer and Inverter Switching with logic - del20016

Opamp Supply on Buffered Virtual Ground

This gnd. can sink and source in a couple of mA. You can use it with low power opamp circuits for portable battery operated devices. This creates a virtual +/- 6 V dual supply from a 12V battery. This may be needed in cases where some instrumentation opamps need the negative supply or your design demands a measurement around zero.

You may get a more loadable ground using a Power Opamp, i have not tried. The above circuit gnd cannot be used as a return path for LED's or Relays. You can drive these, between VCC-VDD, but translate levels to drive them.

Friday, April 07, 2017

Relay Driver - Electromagnetic

This circuit is a standard way of driving Small Power Relays from Control Signals generated by Logic or Opamp Circuits.

C2 and R5 form a snubber which improves the life of the metal contacts, the contacts can erode due to sparking when switching inductive or even big loads. reduces EMI_RFI.

Basics of Electronics

The Electromagnetic Solenoid Coil is rated by Volts and Ohms. If you choose 12V ensure a stable 12V is provided, more voltage will heat coil, less voltage will cause sparking or will drop out the magnetic holding. A high coil resistance is better as the heat will be less and power consumption of your design is low.

Basic Relay or Solenoid Driver

Q2 is any 500mA-50V-NPN device. For a relay drawing 100mA-12V use a 200mA-50V device or better. D1 is a freewheeling diode, inductive kickback diode or snubber or something that stops the coil from zapping the Q2. Q1 and Q2 form a Darlington pair to amplify the low current drive of some CMOS gates.

Infrared Optical Proximity Switch

R2 and R1 is to hold the bases to ground and avoid floating or else they will pick up noise and relay will chatter..... the contacts will spark ....... the motor or heater will fail to work well......... and your product will get rejected ........... the payments will be held up ...... the customer may even ........................... stop that right now !

R3 and C1 is a dampener for the signal so that quick relay operations can be avoided, this is important if your relay is driving a three phase contactor which runs a huge Motor. C1 can be increased if required. When huge loads are switched on-off in a factory, lots of spikes and drop outs will reset timer and logic circuits, this will turn on off above relay ... leading to the load switched by this circuit going on-off. This may even lead to a Oscillation with the spikes as feedback which can cause great trouble during the troubleshooting process. R4 limits current.

Wednesday, March 15, 2017

Millivolt Milliamp Source - Field Calibration Current Loop

This is easy to rig millivolt source for field calibration or troubleshooting of 4-20 mA current loops. Here a Darlington pair is used for current amplification which reduces the Ib error as gain is very high.

EE Design Library - Electronic Product Design Resource.

Millivolt Source - Field Callibration Current Loop

A rotary switch selects, 4-12-20 mA Preset points. A Bourns multi-turn wirewound Pot can also be used with a digital dial. Enclose in a dust proof handheld box. Read more on process calibration.

A mA source terminated with a 10 Ohm or 100 Ohm can turn it into a mV Source. The Resistor should be above 1W and has good temperature stability. Use MFR 1 % many in parallel to get a Instrument shunt if you do not get any.

Thursday, March 09, 2017

Analog and Digital Voltmeter using ICL7107

This Circuit  is a DPM or digital panel meter. It has a analog bar graph display and a 3-1/2 digit digital display. ICL7107 is used in the 200mV configuration.

U4A opamp LF353 amplifies the 200mV Full scale input to the level required for the LM3914 display circuit. D13-D14 are clamping protection diodes. Adjust P1 trimpot for a reading of 1000 counts when a 100.0 mV signal is fed at Vin. Adjust R8 trimpot to get the 5th led  to just turn on at 100mV input.

Analog and Digital Voltmeter using ICL7107

A combination of digital and analog display is helpful for quick decision making. Analog indicates even from a distance the process dimension.

Human Brain understands analog better. The digital is required to note down and record values for determining a setpoint or performance of a system.


Sometimes a analog recorder with a ink-pen plot against time is a very good way of process analysis. Many systems are better studied using graphs not tables and lists of numbers. A Computer based data-logger gives greater power to this methods. You can measure and plot graphs of various types and at different points and for much longer periods.

This is a part of my Build a DMM or Digital Multi Meter

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