Tuesday, August 16, 2016

Single Digit Voltmeter with LM311

I wanted to design a logic probe as a tutorial, but there were many good ones in the web so i have tried to design a single digit voltmeter. This circuit is a design, i am unable to test it now, later if i test it and find mistakes i will update this page. You can help me by pointing out the errors.

Single Digit Voltmeter with LM311
First bear it in mind that it is a single digit voltmeter which is 0-9 counts only on the positive side, that is it can measure +0 to +9V DC +/- 1V error. That may not be practical for the cost of the components above. It may be used as a toy logic probe. The reason for the circuit is not for usage, but to give design ideas. The methodology used is Gut Feel - Thumb Rule method.


Sunday, August 14, 2016

LED Voltage Level Indicator

This circuit is derived from a Siemens Application Note 1974. This circuit uses common components of today.

The circuit is here as it is of high educational value. I have not tested it. You can 'simulate and test' or 'wire it up and try' and let me know how it worked. The Circuit is also a simple analog to digital converter. You can use optos in place of LEDs.

Battery Level Indicator

T1 and T2 make a differential amplifier. T3, T4 and T5 driving the LEDs are comparators.  When input voltage is increased T1 is turned on which leads to more base current for T3 which Lights LED1. When input voltage is less T2 turns on as it gets a better base current from P3 which turns on LED2 via T4. When both LEDs are off T5 gets biased as no drop across R5 which lights the LED3 thru T5 hopefully.

LED Voltage Level Indicator

What you need to know is a small current Ib thru the base-emitter path in the direction of the emitter arrow will lead to a large Current Ic thru the emitter-collector path in direction of arrow. Ic = B * Ib where B - beta is the DC current gain, it could be 100-400

Fluid or Water Level with Reed Relays 

Beta is different in each transistor you buy and varies with the test conditions and even with temperature and age. The LED1 and LED2 will indicate above or below Limits set by P2 and P1. The Limit Threshold itself is set at P3 i think. LED3 will light when Hi LED and Lo LED both are off.

The applications of this circuit are FM tuning indicator, Stereo Balance Indicator (Wire T2 like T1 then we get two channel inputs) and battery level indicator.

Saturday, August 13, 2016

5V -1A Power Supply using LM2575

A Power Transistor which is having a drop of 4 Volts across it and passing 3 amps thru it, may dissipate around 12 Watts of Heat, This is the problem in Series Regulators. While a Saturated Transistor or Mosfet with 1 Volts across and 3 Amps Thru will be just 3 Watts. But then a fully on transistor or mosfet cannot be controlled or regulated, for that we turn it ON and OFF very fast so that the right amount of current or voltage is delivered.

Power Electronic Circuits  

5V -1A Power Supply using LM2575

The way this is done is PWM - Pulse Width Modulation. In this the mosfet or transistor is switched ON-OFF at say 100 kHz, but the ON duration is varied to control the output. The longer the duration of ON time more energy or punch is transferred. Switching losses will be present depending on how fast the rise and fall times of the pulses are.

The Pulsed AC or Chopped DC can be smoothed to the Average with Inductors and Capacitors. The reactive pulses of the Inductor has to be absorbed by a Schottky Rectifier 1N5817 -- 20V-1A fast switching diode with low switching losses.

This circuit is derived from an application note of LM2575, It is a Power Switching Regulator from National Semiconductor The details are here LM2575

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

Hobby DIY Electronics

delabs Circuits