Simple Metallic Pipe Detector

Here is a simple circuit diagram project of metallic pipe detector circuit. This circuit uses a 15-kHz oscillator coil.

Simple Metallic Pipe Detector Circuit Diagram:


When metal placed ixi the energy field is withdrawn, the oscillator voltage is rectified and compared to a reference. A drop in oscillator voltage therefore operates comparator IC2 and D4 (LED) extinguishes. L1= 500 turns enameled copper wire. 0.2 - 0.3mm diameter. on ferrite rod 200mm long and 10 mm diameter.

Metal Detector Using With TDA2822

This is electronic circuit project of metal detector using with TDA2822 and few NPN transistors. There is a small arrow connected from the Emitter of the T3 to the 10n Capacitor C4. That arrow is simply indicating signal flow as right to left in that particular wire, which is different from the remaining circuit's left to right.

Metal Detector Using With TDA2822 Circuit Diagram:


The most critical component is the coil L1. The text says 15 turns and the schematic says 20 turns. I suppose either will work, but VC1 will be different. I would try 15 turns first. 2) VC1 is 0-22pF. A 0pF minimum is unnecessary, and it would be a difficult to find part. With a 15 turn coil, the nominal setting for VC1 is about 18pF, so a 5-15pF part in parallel with a 5 or 10pF fixed capacitor will be easier to find and easier to adjust. 3) The 4 inch coil and 5.5MHz operating frequency will give a very limited detection distance. Might be good for finding nails in the wall, behind the plaster. 4).

 The oscillator V+ should be regulated and isolated from the audio amplifier. Otherwise zero beat will interact with the audio, since the audio amplifier can draw a few hundred mA. 5) R2 value (330R) is wrong. It would prevent T1 from ever conducting. Maybe it's 330K. 6) C11 and C13 are basically in parallel. VR1/C11/C13 low pass frequency varies from infinity to 5kHz with the volume setting. 7) The power bypass capacitors C1 and C14 are unlikely to be effective at the 5.5MHz operating frequency. The detection oscillator will tend to lock on the ceramic filter's frequency. The circuit needs a few 0.1uF (100n) caps to filter the oscillator V+.

Electronic Bell with Two 555 Timers

Here is a very simple Electronic Circuit Diagram of Bell circuit uses two 555 timers. The frequency is controlled by the capacitors that must be preserved almost identical in value to each other for best results. 

Electronic Bell with Two 555 Timers Circuit Diagram:

555 timers

Fine tuning is done with R1 and R2. The decay time is controlled by R3.

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.