delabs Circuits

Saturday, April 11, 2015

Battery Level Indicator

This circuit uses a LM339, a quad comparator. LM339 can work on single or dual supplies, it has a open collector output that can drive 15mA, low power consumption. The circuit is an untested design but it should work. I did it as many searches were made in my webpages with these keywords.

Mains Voltage and Power Circuits - Similar circuits for Mains Voltage Monitoring.

There are many better circuits in the various circuit archives i have linked on the front page, you just have to look around. When you measure the open circuit voltage of a battery with a high impedance DMM (10M), the value may be a bit misleading. Apply a dummy load to bleed the battery a bit so that proper readings can be taken on Load. The load below is a 100 ohms wire-wound fusible ceramic resistor which will heat a bit when you test 12V batteries.
Battery Level Indicator

Theory of Operation.

R16 a 5W ceramic wire wound bleeder or dummy load. R15 is a part of an attenuator for obtaining ranges. D2 is a protection clamp diode. R10-D1 forms the 5V reference for comparators. Then an attenuator obtains 1.2, 1.4, 1.6, 1.8 V steps for each comparator. This circuit is similar to Audio Level meter or VU meter circuit.

Comparators in Interface Circuits

The comparator compares the battery sample voltage to the fixed reference step. If '+' pin is more positive than '-', or is '+' is more dominant, then output goes floating 'open collector', so No LED light . But if '-' is more dominant the output transistor of comparator goes low impedance or saturates or turns 'ON'. But only spec current can be switched, do not compare with electrical switch 'ON'. Also on a dual supply 0V is more dominant or positive compared with -12V, even though it appears -12V is a big number. The direction of current is what decides, all measurements are relative.


Thursday, April 09, 2015

Differential to TTL convertor using LM339

Some outputs are via Dual Differential Line Driver type DS8830. This device will interface with standard TTL systems.

Differential to TTL convertor using LM339

The differential outputs are balanced and are designed to drive long lengths of coaxial cable, strip line, or twisted pair transmission lines with characteristic impedances of 50 ohms to 500 ohms. Differential transmission is superior to single wire transmission in that it nullifies the effects of ground shifts and noise signals which appear as common mode voltages on the transmission line.

Mixed and Interface Circuits

If the signal voltage at the end of the line is found to be of insufficient magnitude then the following circuit may be used (at the recipient equipment end) to boost the levels.

Tuesday, April 07, 2015

Simple Digital Event Counter

The basic digital circuits are Flip Flop and Counter, both are here. This circuit can be cascaded to make even a 6 digit event counter, even a simple frequency counter can be made.

These are best done with microcontrollers today. Then what if you have to design your own microcontroller on a FPGA, so the basics have to be sound, hence you have to know what gates, flip flops and counters are.

Simple Digital Event Counter

See the seven segment display. Inc, Dec, and Set buttons are momentary acting and Clk Button is latching type. The Dip Switch in the also can be set.

a. - Set the DIP Switch as you like and then Press the Set button. The BCD value will be at the 4029 output, The Decimal value will be seen in the seven segment Display. Now try for different dip switch settings and see the BCD and Decimal output.

b. - Now Press The Inc and Dec pushbuttons. Set it to Increment up-count or Decrement which is down-count. This is a simple flip flop control.

Simple Digital Event Counter

c. - Now Click the Clk - clock or count button, the switch will latch, press it again to release. If you toggle it once the counter will get a single pulse and it will count it, see the BCD and decimal displays. Now you turn it on and leave it, the counter will keep counting one per second till you turn it off, the clock nand gate is wired to be an oscillator.

More here - Digital Timers, Counters and Clocks

The decimal point LED of display is given to Carry Out pin of 4029 so observe this at 9 and 0 or transitions.

Add 104 CD, 0.1uF ceramic disc cap to all the ICs across the supply pins. Also add a 104 CD cap across Inc switch and one across the Set switch for power on default settings.

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