Op Amp Cell Phone RF Signal Detector
Revision 10-16-2012
Youtube Video: http://youtu.be/kXJJauAWrzc
Online CircuitLab Circuit Schematic: https://www.circuitlab.com/circuit/uq4jyh/my-lm358-cell-phone-rf-detector/
This beginner electronics circuit is a quick fun
breadboard circuit that uses an operational amplifier (Op-Amp) to sense
the presence of an activated cell phone from a distance of several
meters. The simple circuit can detect any activity of a
mobile phone such as incoming or outgoing voice, voicemail,
texting, and data. I can imagine someone using such a circuit
device on an airplane to scan you or your area if they suspect you
are using your phone while it is not in airplane-mode. Or perhaps
your teacher suspects you are texting while in class. Sometimes my
imagination and I don't get along.
If a cell phone signal is detected the circuit will blink a LED
and or a sound buzzer. Keep in mind that the phone must be
transmitting and the only time a phone is transmitting is when it
is receiving or sending voice, text, internet or data.
Sensitivity can be adjusted on the circuit by adjusting the
potentiometer. This circuit is made very simple using the least
amount of components. The components used are very inexpensive and
readily available.
R5 Potentiometer (POT):
Adjust the POT until the LED is off with only an occasional flicker. R5 can be substituted
with fixed resistors.
Antenna: Experiment
with the antenna length. You can search
the internet on antenna design, tutorials, and calculators to find the best
length or shapes taking into account the frequency involved and chip-breadboard
layout.
When I get a chance I'll build one that is more receptive to higher frequencies of 4G carriers. The circuit above was tested on a slower 3G T-Mobile service.
Example Circuit 1
Example Circuit 2
This circuit works as good as circuit
1.
ENJOY!
Where to buy parts
You may be able to purchase the whole kit from Electronix Express http://www.elexp.com/ . Try emailing their sales department and include the parts list below. The parts list below uses all Electronix Express part numbers for easier purchases.
Other great distributors
http://www.digikey.com
http://www.jameco.com
Distributor Electronix Express - Parts List
Electronix Express - LM358 Cell Phone Detector Custom Kit
Item
|
Reference Designator
|
Part Description
|
Quantity Used
|
Electronix
Express
Part Number
|
1.
|
U1
|
LM358AN, Dual OpAmp Single Supply 8-Pin Dip, Thru-Hole,
|
Qty 1
|
10358
|
2.
|
R1, R2, R3
|
6.8M Resistor, Carbon, 6.8M Ohm, 1/4 Watt, 5%,
Thru-Hole, Bulk,
|
Qty 3
|
130056.8M
|
3.
|
R4
|
1K Resistor, Carbon, 1K Ohm, 1/4 Watt, 5%, Thru-Hole,
Bulk,
|
Qty 1
|
130051K
|
4.
|
C1, C2, C3
|
0.1uF Capacitor, Ceramic, 0.1uF 50 Volt, Z5U, 20%
Radial, Bulk,
|
Qty 3
|
14MN050.1U
|
5.
|
R5
|
500K Ohm Resistor Potentiometer Trimmer, 0.5Watt, 10%,
1 single turn, 2.5mm pin spacing, Thru-Hole, Bulk,
|
Qty 1
|
18STC500K
|
6.
|
D1
|
LED Green Color T-1 3/4, Thru-Hole, Bulk,
|
Qty 1
|
08L53GD
|
7.
|
9V
|
9 V Snap Connector Clip, 4 Inch Length 26 AWG Lead Wire
|
Qty 1
|
2801BSNAP
|
8.
|
9V
|
9 Volt Battery,
|
Qty 1
|
2800RG9
|
9.
|
|
Breadboard 170 Tie Point
|
Qty 1
|
03MB101
|
10.
|
|
22 AGW Hook Up Jumper Wire Kit
|
Qty 1
|
2700MJW70
|
11.
|
|
Wire Cutter Stripper, 26-16AWG
|
Qty 1
|
060220
|
12.
|
|
Small DC Buzzer, Built in Driver Circuit
|
Qt1
|
26PZ06
|
End of Parts List
My Generic Parts List
Use this parts list for purchasing from any distributor. It is the same parts but uses generic part numbers.
http://www.digikey.com
http://www.jameco.com
Op Amp Cell
Phone RF Signal Detector Revision 10-16-2012
|
|
My cost
|
Schematic
Reference Designator
|
Part
|
Description
|
Quantity Used
in Circuit
|
Cost Each
|
Cost Total
|
Note
|
U1
|
LM358AN
|
Dual OpAmp Single Supply 8-Pin Dip,
Thru-Hole
|
1
|
$0.19
|
$0.19
|
|
R1, R2, R3
|
6.8M Resistor
|
Resistor, Carbon, 6.8M Ohm, 1/4 Watt, 5%,
Thru-Hole, Bulk.
|
3
|
$0.03
|
$0.09
|
This value may be substituted with what you
have available, such as 1M – 10M.
|
R4
|
1K Resistor
|
Resistor, Carbon, 1K Ohm, 1/4 Watt, 5%,
Thru-Hole, Bulk.
|
1
|
$0.03
|
$0.03
|
This value may be substituted with what you
have available, such as 330 – 5K.
|
C1, C2, C3
|
0.1uF Capacitor
|
Capacitor, Monolithic Ceramic, 0.1uF 50
Volt, Z5U, 20% Radial, Bulk
|
3
|
$0.06
|
$0.18
|
This value may be substituted with what you
have available.
|
R5
|
500K Resistor Potentiometer Trimmer - Thumb
and screwdriver adjustment
|
3352 - 3/8 ” Trimming Potentiometer 500K
Ohm, 0.5Watt, 10%, Thru-Hole, Bulk,
Single-Turn, Cermet, Thumb and screwdriver adjustment
|
1
|
$0.90
|
$0.90
|
This value may be substituted with what you
have available, such as 10K – 1M. Or inexpensive resistor could replace this.
|
D1
|
LED Any Color
|
LED T-1 3/4, Thru-Hole, Bulk
|
1
|
$0.05
|
$0.05
|
Any color or size.
|
--
|
9 V, Snap Connector
|
9 V Battery Snap Clip, 4 Inch Length 26 AWG
Lead Wire
|
1
|
$0.30
|
$0.30
|
|
--
|
9 Volt Battery
|
9 Volt Battery
|
1
|
$1.00
|
$1.00
|
|
--
|
Breadboard
|
170 Tie Point Breadboard
|
1
|
$0.95
|
$0.95
|
|
--
|
22 AGW Wire
|
Hook Up Jumper Wire, 22AWG, Solid, Red
Hook Up Jumper Wire, 22AWG, Solid, Black
Hook Up Jumper Wire, 22AWG, Solid, Yellow
|
Pre-stocked
|
|
0
|
You can purchase 25’ spools of different
colored wire for a few dollars each or purchase “jumper wire kits”
|
--
|
Wire Cutter Stripper
|
Wire Cutter Stripper, 26-16AWG
|
Pre-stocked
|
|
0
|
|
--
|
Miniature Potentiometer Trimmer Tool
|
Miniature Potentiometer Trimmer Tool -
Screwdriver
|
|
|
0
|
$0.40 Used to adjust trimmer if using a
non-thumb adjustable trimmer.
|
--
|
Optional Buzzer
|
|
|
|
0
|
I used a 14 year old buzzer I found lying
around. I’ll purchase a buzzer online and provide a part number in the
future.
|
Total Cost
|
$3.69
|
|