Simple Liquid Level Monitor

This monitor uses a common 7 41 amp configured as a comparator and a low cost nontransistor as an output driver. With no liquid detected, a voltage of about 2. 92 V is present in the op amp`s inverting input at pin 2. The 100-KO resistors establish a reference voltage of +2. 5 V at the noninverting input at pin 3 of the op amp. Under those conditions, the op amp`s output is -3.56 V, which keeps the 2N2222 transistor turned off and the voltage across its 1-KO output load resistor at 0 V.

Simple Liquid Level Monitor Circuit Diagram:

Liquid Level Monitor

When liquid reaches the probes, the 3.3-MO and 22-KO resistor circuit conductively connects to ground. When enough current, about 1.4 p.A, flows through the liquid, the small 30 m V drop developed across the 22-KO resistor drives the op amp to deliver an output voltage of about 4.42 V. This voltage then drives a 2N2222 transistor into saturation, which generates a voltage drop of about 3.86 V across its 1-KO output load resistor.

Voltage Regulator with Pass Transistor Using LM317T

The LM317T output current can be increased by using an additional power transistor to share a portion of the total current. The amount of current sharing is established with a resistor placed in series with the 317 input and a resistor placed in series with the emitter of the pass transistor.

Voltage Regulator with Pass Transistor Circuit Diagram:

Transistor Circuit Diagram

In the figure below, the pass transistor will start conducting when the LM317 current reaches about 1 amp, due to the voltage drop across the 0.7 ohm resistor. Current limiting occurs at about 2 amps for the LM317 which will drop about 1.4 volts across the 0.7 ohm resistor and produce a 700 millivolt drop across the 0.3 ohm emitter resistor. Thus the total current is limited to about 2+ (.7/.3) = 4.3 amps. The input voltage will need to be about 5.5 volts greater than the output at full load and heat dissipation at full load would be about 23 watts, so a fairly large heat sink may be needed for both the regulator and pass transistor.

 The filter capacitor size can be approximated from C=IT/E where I is the current, T is the half cycle time (8.33 mS at 60 Hertz), and E is the fall in voltage that will occur during one half cycle. To keep the ripple voltage below 1 volt at 4.3 amps, a 36,000 uF or greater filter capacitor is needed. The power transformer should be large enough so that the peak input voltage to the regulator remains 5.5 volts above the output at full load, or 17.5 volts for a 12 volt output. This allows for a 3 volt drop across the regulator, plus a 1.5 volt drop across the series resistor (0.7 ohm), and 1 volt of ripple produced by the filter capacitor. A larger filter capacitor will reduce the input requirements, but not much.

Generating a Delayed Pulse Using The 555 Timer

The circuit below illustrates generating a single positive pulse which is delayed relative to the trigger input time. The circuit is similar to the one above but employs two stages so that both the pulse width and delay can be controlled.

Generating a Delayed Pulse Circuit Diagram:

Pulse Circuit Diagram

When the button is depressed, the output of the first stage will move up and remain near the supply voltage until the delay time has elapsed, which in this case is about 1 second. The second 555 stage will not respond to the rising voltage since it requires a negative, falling voltage at pin 2, and so the second stage output remains low and the relay remains de-energized.

At the end of the delay time, the output of the first stage returns to a low level, and the falling voltage causes the second stage to begin it's output cycle which is also about 1 second as shown. This same circuit can be built using the dual 555 timer which is a 556, however the pin numbers will be different.

12V DC to 24V DC Voltage Booster

Here is a simple circuit for boosting 12 V DC to 24 V DC .The circuit is designed straight forward and uses few components.With few modifications the circuit can be used to boost any voltages.

The transistor Q1 and Q2 (D1616)  essentially drives the primary of the transformer.The diodes rectifies the output of transformer to obtain a 24V DC at the output load(here a fan).The capacitors filter away noise and harmonics away from the output.

Simple Voltage Booster Circuit Diagram :

Booster Circuit Diagram 


  • The component values are not very specific here.We can use any NPN power transistors like D1616,2N 3055,C2236,SL 100 etc for Q1 and Q2.
  • The transformer can be any center tapped 5A transformer with a  7:1 winding ratio.
  • The diodes can be 1N 914 ones.
  • In fact you can easily assemble the circuit from the components in your electronics junk box.
  • By experimenting on the tranformer winding you can get different boost ratios.
  • For high current (around 5A)  games use 2N 3055 transistor or more powerful Darlington pairs for Q1 and Q2.

Battery-Powered Night Lamp

This circuit is usable as a Night Lamp when a wall mains socket is not available to plug-in an ever running small neon lamp device. In order to ensure minimum battery consumption, one 1.5V cell is used, and a simple voltage doubler drives a pulsating ultra-bright LED: current drawing is less than 500µA. An optional Photo resistor will switch-off the circuit in daylight or when room lamps illuminate, allowing further current economy. 
This device will run for about 3 months continuously on an ordinary AA sized cell or for around 6 months on an alkaline type cell but, adding the Photo resistor circuitry, running time will be doubled or, very likely, triplicated.
Battery-Powered Night Lamp Circuit Diagram:

Lamp Circuit Diagram

Circuit Operation:
IC1 generates a square wave at about 4Hz frequency. C2 & D2 form a voltage doubler, necessary to raise the battery voltage to a peak value able to drive the LED.

  • IC1 must be a CMos type: only these devices can safely operate at 1.5V supply or less.
  • If you are not needing Photo resistor operation, omit R3 & R4 and connect pin 4 of IC1 to positive supply.
  • Ordinary LEDs can be used, but light intensity will be poor.
  • An ordinary 1N4148 type diode can be used instead of the 1N5819 Schottky-barrier type diode, but LED intensity will be reduced due to the higher voltage drop.
  • Any Schottky-barrier type diode can be used in place of the 1N5819, e.g. the BAT46, rated @ 100V 150mA.
Parts List:

R1,R2___________1M   1/4W Resistors
R3_____________47K   1/4W Resistor (optional: see Notes)
R4____________Photo resistor (any type, optional: see Notes)

C1____________100nF  63V Polyester Capacitor
C2____________220µF  25V Electrolytic Capacitor

D1______________LED  Red 10mm. Ultra-bright (see Notes)
D2___________1N5819  40V 1A Schottky-barrier Diode (see Notes)

IC1____________7555 or TS555CN CMos Timer IC

B1_____________1.5V Battery (AA or AAA cell etc.)

Simple Charger for All Battery Types

Here is a Very Simple Electronic Circuit Diagram Project of  Simple Charger for All Battery Types. Note that the stability is observed when the load current and will change slightly of the supply voltage. Likewise, the fact is usually overlooked, but if you want a perfect stability – stabilize the power supply. Calculation of the current is very simple – the current in amperes is equal to 1.2 divided by the resistance R1 in Ohms.

Simple Charger for All Battery Types Circuit Diagram:

Circuit Diagram

 To display the current used transistor (germanium necessarily because of the low voltage opening) that allows you to visually observe the currents to 50 mA. Diode D1 and F2 fuse protects the charger from the battery reverse. Capacitance C1 is selected from the formula: 1 amp should 2000uF.

The advantages of the proposed device: short-circuit protected it does not matter the number of elements in rechargeable battery and type – can be charged and sealed acid and lithium 12.6 3.6 and 7.2 V alkaline Switch current should be included exactly as shown on the chart – in order to remain in any manipulation of the resistor R1. The use of alternating low-impedance resistor is undesirable because of instability of sliding contact with load currents over 0.2 A.

High Voltage Generator

This high voltage generator was designed  with the aim of testing the electrical break-down protection used on the railways. These  protection measures are used to ensure that  any external metal parts will never be at a  high voltage. If that were about to happen,  a very large current would flow (in the order  of kilo-amps), which causes the protection  to operate, creating a short circuit to ground effectively earthing the metal parts. This hap-pens when, for example, a lightning strike hits  the overhead line (or their supports) on the  railways.

This generator generates a high voltage of  1,000 V, but with an output current that is limited to few milliamps. This permits the electrical breakdown protection to be tested with-out it going into a short circuit state. The circuit uses common parts throughout: a  TL494 pulse-width modulator, several FETs or  bipolar switching transistors, a simple 1.4 VA  mains transformer and a discrete voltage multiplier. P1 is used to set the maximum current  and P2 sets the output voltage.

High Voltage Generator Circuit Diagram:
Generator Circuit Diagram
The use of a voltage multiplier has the advantage that the working voltage of the smoothing capacitors can be lower, which makes them easier to obtain. The TL494 was chosen  because it can still operate at a voltage of  about 7 V, which means it can keep on working even when the batteries are nearly empty.  The power is provided by six C-type batteries, which keeps the total weight at a reason-able level.
The 2x4 V secondary of AC power transformer  (Tr1) is used back to front. It does mean that  the 4 V winding has double the rated voltage  across it, but that is acceptable because the  frequency is a lot higher (several kilo-Hertz)  than the 50 Hz (60 Hz) the transformer is  designed for. The final version also includes a display of the  output voltage so that the breakdown volt-age can be read.
From a historical perspective there follows a  bit of background information. In the past a different system was worked  out. Every high-voltage support post has a  protection system, and it isn’t clear when  the protection had operated and went into  a short-circuit state due to a large current  discharge.
Since very large currents were involved, a certain Mr. Van Ark figured out a solution for this.  He used a glass tube filled with a liquid containing a red pigment and a metal ball. When  a large current discharge occurred the metal  ball shot up due to the strong magnetic field,  which caused the pigment to mix with the liquid. This could be seen for a good 24 hours after the event. After a thunder storm it was  easy to see where a discharge current took  place: one only had to walk past the tubes  and have a good look at them.
Unfortunately, things didn’t work out as  expected. Since it often took a very long  time before a discharge occurred, the pigment settled down too much. When a dis-charge finally did occur the pigment no  longer mixed with the liquid and nothing was  visible. This system was therefore sidelined,  but it found its place in the (railway) history  books as the ‘balls of Van Ark’.link