Magnetojector (INS047E)

This is a different signal injector, as it does not need to connect to the analyzed circuit. What it does is to inject a signal into components that have coils and that is why they can pick up signals through a magnetic field. Simple to assemble, it can be very useful in the assembler's and electronic repairman’s workbench.

The circuit shown generates a signal which is applied to a coil, from which it can be radiated to a test circuit.

The signal creates a low frequency field that can be picked up by transducers and inductive components without connection such as pickup coils, recorder heads, microphones and others, as shown in Figure 1.

 

   Figure 1 - Applying the signal
Figure 1 - Applying the signal

 

 

 

How it works

The circuit consists of a simple audio oscillator with complementary transistors where the frequency is determined by the setting of P1 and the value of the capacitor C1.

The circuit load is not a loudspeaker, but a coil that can be wound on a nail or a screw with thin wire (28 to 32).

They are wound from 50 to 100 turns of the indicated wire.

The signal generated is rich in harmonics, which can excite both audio and RF circuits.

This allows tests on several circuits to be made, with direct pickup in cases of receivers or other more sensitive circuits.

Circuit power can be supplied with 2 or 4 small batteries.

 

Assembly

In Figure 2, we give the complete diagram of the injector.

 

   Figure 2 - Circuit diagram of the magnetojector
Figure 2 - Circuit diagram of the magnetojector

 

 

As it is a very simple assembly, even an assembly on a terminal strip, as shown in Figure 3, is possible.

 

   Figure 3 - Terminal strip assembly
Figure 3 - Terminal strip assembly

 

 

For a more elaborate assembly we have a printed circuit board which is shown in Figure 4.

 

   Figure 4 - Printed Circuit Board
Figure 4 - Printed Circuit Board

 

 

Observe the positions of the transistors in the assembly.

 

In Figure 5, we have details of the construction of the transducer.

 

 

Figure 5 - The transducer
Figure 5 - The transducer

 

 

The resistors are 1/8 W and the capacitor can be ceramic or polyester.

A power supply for the circuit.

 

   Figure 6 - A power source for the injector
Figure 6 - A power source for the injector

 

 

To test, simply connect and approach the injection coil of an AM radio tuned out of station.

 

Q1 - BC548 - NPN general purpose transistor

Q2 - BC558 - general purpose PNP transistor

S1 - Single switch

B1 - 3 or 6 V - 2 or 4 small battery cells

P1 - 100k ohms - potentiometer

X1 - injection coil - see text

R1 - 10 k ohms - resistor - brown, black, orange

R2 - 1 k ohms - resistor - brown, black, red

C1 - 100 nF - polyester or ceramic

 

Miscellaneous:

Printed circuit board or terminal bridge, battery holder, mounting box, wires, welding, etc.