This circuit uses a 555 timer IC to generate noise that modulates a transistor oscillator, producing a signal that can jam cell phone frequencies between 800 MHz and 2 GHz when a simple antenna is connected. The components can be built onto the 555 IC itself using surface mount parts. The jamming range is around 10-15 feet, enough for most purposes. The current drain is high so a battery only lasts about an hour.

1. Simple Cell Phone Jammer
Posted Feb 16, 2012 at 3:59 pm
Figure 1
A “Cell Jammer” is just way of saying “Dirty Transmitter” which happens to transmit within the Cellular
Phone Bands. Reality is, the dirtier the better.
The 555 timer [8 pin] IC simply makes a noise. It’s coupled via C4 [electrolytic] to modulate
the MRF transistor oscillator. With C1 set at roughly 1/3rd, you will be close to 900 MHz. By sweeping the
C1 trimmer capacitor, you can swing the output frequency from 800 MHz to 2 GHz with the transistor and
values shown.
You could replace the 555 chip with an electret microphone and listen to yourself talk on a scanner, so
the unit could easily couple as a UHF Bug.
Instead of a single Tapped Coil, I’ve used two molded inductors for ease of construction.Values for
C1,C2,L1,L2 are critical for the frequency range.
You might want to build the unit into a metal box, add an on/off switch in the batteries + line, and maybe
even add a LED. Connect an old 800 MHz cell phone antenna to C5.
Would you believe the whole thing can be built on top of the 555 IC itself when using surface mount
components, and the lot will fit onto a nine volt battery clip. Output is reasonably good, although the
current drain is a bit high, so a new 9 Volt battery will only run about an hour, [if you are lucky].
The “Cell Kill Distance” is around 10 – 15 feet, ample for most purposes.
Designer & Author: Special thanks to Laszlo Kirschner.

2. USB Charger for Mobile Phones
Dileep Chacko
All of us worry about our mobile phone draining out of charge while travelling. In such a
situation, this SMPS-based USB charger powered by just two AA-size batteries will come
handy. The advantage of SMPS is high efficiency and low cost. Of course, most mobile
phones can also be charged through the standard USB port available in desktop and laptop
computers.
A unit load is 100 mA in USB 2.0, and 150 mA in USB 3.0. An individual device may draw a
maximum of 5 units load (500 mA) from USB 2.0 and 6 units (900 mA) from USB 3.0.
This USB charger for mobile phones operates off a 2.4V or 3V battery. It is designed around
an average input-current-controlled buck-boost DC-DC converter LTC3127 (IC1) and some
discrete components. The circuit converts 3V or 2.4V input into 5V output.
Pins SW1 (pin 2) and SW2 (pin 11) are used to connect the inductor. SHDN (pin 4) shuts
down the output of LTC3127 when low. Pin 5 is used to change the mode of operation
between PWM and burst modes. If Mode pin is low the mode will be PWM; when it is high
the mode will change to burst mode. PROG (pin 6) is used to set the average input current
limit threshold. Vc (pin 9) is used to connect the compensation components, which impart

3. stability to this regulator.
The values of R1 and R2 decide the output voltage level as follows:
VOUT = 1.195×1 + R2R1
You can select appropriate values of R1 and R2 to get 5V output (VOUT).
car reverse horn:
Most mobile phones have a USB male connector for charging, so a female connector is
required for the charger side. Assemble the circuit on a small PCB and enclose in a suitable
cabinet. Use a USB female connector and solder the connections as shown in the figure. The
table gives the pin details of a USB connector. For powering the circuit, use an AA-size
battery pack having either two 1.5V alkaline batteries or two 1.2V (Ni-Cd or Li-ion)
batteries.
he circuit is connected via brake switch of the car/ three-wheeler.

4. When you reverse your vehicle, the circuit is connected to the battery of the car through the
brake switch. The AMV oscillates and produces an audio frequency, which is given to speaker
driver transistor T1 to generate a beeping tone. This tone can be altered by changing the values
of capacitors C2 through C4 in multivibrator circuit.
Assemble the circuit on a general-purpose PCB and enclose in a suitable box. Connect 12V DC
power supply to the circuit through the brake switch. When you reverse your car the circuit gets
12V required for its working. Place the cabinet in the vehicle such that it produces sound at the
rear while reversing the car.
aj Gorkhali
Door alarm:This circuit can be operated by any kind of switch. For example,
it can be used in a shop to warn that a customer is waiting, with a micro-switch attached to
the shop door. Or you can fix a suitable switch at the front gate to inform that visitors are
waiting.
The circuit is built around two ICs and some discrete components. One is CMOS 14-stage
ripple-carry binary counter/divider and oscillator CD4060 (IC1) and another is quad 2-input
NOR gate CD4001 (IC2).
The sounds are generated by an oscillator built around IC1. The frequency of the oscillator
is determined by the values of capacitor C1 (4.7n) and resistor R2 (4.7k) as follows:
Frequency (f) =1/(2.2 R2xC1)
With the values given in the circuit, the clock’s frequency is approximately 20 kHz. This
frequency is divided into four stages of binary division before we see it at Q4 output (pin 7)

5. of IC1. Four binary stages are equal to division by 16, so the signal at pin 7 of IC1 has a
frequency of 1.25 kHz. This is comfortably within the audio range and makes a suitable
basic frequency for the rest of the circuit’s operation.
To obtain a two-tone signal, you require a second frequency. This is picked up from output
Q6 at pin 4, which is approximately around 300 Hz. Further along the chain the frequencies
drop below the audio range. For example, at Q13 output of IC1, the frequency is
approximately 2.44 Hz. This is inaudible, but is useful enough for controlling the two-tone
effect. This frequency at Q13 is used here as a control signal.
The two audio signals from pins 7 and 4 are not fed to a pair of NOR gates in IC2 (gates N1
and N3) simultaneously. Gate N1 receives Q13 directly, while gate N3 receives Q13 after it
has been inverted by gate N4. Gate N4 has its two inputs wired together so it operates as
an inverter (or NOT) gate.
When the control signal Q13 is low, gate N1 passes the 1.25kHz signal and (since the
inverted control signal is high) output of gate N3 is held low. But when the control signal is
high, the 300Hz signal passes gate N3 and the output of gate N1 is low. The outputs of
gates N1 and N3 are fed to gate N2, which acts as a mixer.
In this way transistor T1 receives the two audio signals alternately. Transistor T1 drives the
loudspeaker LS1 and produces a two-tone sound. There is no volume control in this circuit.
Volume is plentiful with this value of R3 (2.2k), but you can increase the value of R3 to
produce a soft tone.
CASH BOX GUARD
T.K. HAREENDRAN
Most thefts happen after midnight when people enter the second phase of sleep
called 'paradoxical sleep.' Here is a smart security circuit for your cash box that
thwarts the theft attempt by activating an emergency beeper. The circuit can also
be used to trigger any external burglar alarm unit.
The cash box guard circuit (shown in Fig. 1) is built around IC CD4060 (IC1), which has an
inbuilt oscillator and divider. The basic oscillator is configured by a simple resistor-capacitor
(R-C) network. IC CD4060 divides this oscillator frequency into binary divisions, which are
available as outputs.
In light, reset pin 12 of IC1 remains low, which enables the oscillator built around IC1.
However, in the dark, it making all the outputs low. This also stops oscillations of the
internal oscillator.
Working of the circuit is simple. If the cash box is closed, the interior will be dark. Hence in
the dark, the light-dependent resistor (LDR1) resets IC1 and it stops oscillating and

6. counting. At the same time, pins 13 and 14 of IC1 go low. So neither the piezobuzzer (PZ1)
sounds, nor the relay (RL1) energises, indicating that the cash box is closed.
Fig. 1: Cash box guard circuit
If someone tries to open the door of the cash box, light-most probably from the
burglar's pen torch -falls on LDR1 fitted into the cash box. As a result, LDR1 conducts and
pin 12 of IC1 goes low. IC1 starts oscillating and counting. With the present timing R-C
components (at pins 9, 10 and 11), the output timing at pin 14 of IC1 is two-three seconds.
Hence pin 14 of IC1 goes high for two seconds after the door is opened and goes low for
another two seconds. So the piezobuzzer (PZ1) sounds for two seconds and then falls silent
for the following two seconds. This cycle repeats until the cash box is closed.
An optional relay is added for a remotely located audio/visual alert system. For that, a relay
driver circuit built around npn transistor BC548 (T2) is used. The relay is energised by the
output from pin 13 of IC1 for about four seconds after the door is opened and then de-
energised for the following four seconds. You can use this relay to activate another remotely
located audio/visual alert system.
After assembling the circuit on a small PCB, house it in a small tamper-proof box (refer Fig.
2) leaving a little window for LDR1 and a small opening for the piezobuzzer (PZ1). Now fit
the unit inside the cash box (refer Fig. 3) with LDR1 pointing towards the door of the cash
box.

7. Fig. 2: Assemble unit
EFY note. 1. The relay latching facility can be added to the circuit by replacing transistor T2
with a suitable silicon-controlled rectifier such as BT169.
2. By changing the value of resistor R1, you can adjust the light detection sensitivity of the
circuit.
3. If you want to use a 3-pin piezobuzzer device, remove buzzer-driver npn transistor T1
and connect trigger pin of the buzzer directly to pin 14 of IC1. Also connect the positive and
negative terminals of the buzzer to respective positive and negative points of the circuit.
4. Photo-transistor 2N5777 can be used in place of the 10mm LDR1.
5. The complete kit for this circuit is available with Kits'n'Spares.

8. Fig. 3: Unit fitted inside the cash box &
also connected to an external alarm