My most attracted circuit is Mobile bug published in Electronics for You few years back. More than 500 students selected the Mobile bug as their project in Electronics Engineering. Some intelligent students have modified the circuit very interestingly and some have constructed the circuit with professional touch. See how Erna Tamizi from Malaysia constructed the Mobile Bug with professional touch and recorded the Video to show its working.
Click this Link to get the design considerations and trouble shooting tips of Mobile bug
Steve Brown says an inspiring comment on my Mobile Bug circuit published in EFY………..
Congratulations on developing such a simple detector for mobile phone detection.
It has clearly created a lot of interest since you first published in 2008 and i am sure
you must be getting tired of responding to queries and questions about it.
Just wondered if you had carried out further work to make the design work at a lower
battery voltage e.g 3 – 5V (Li Po etc) and make it more band-limited to reduce pick-up
from DECT and WiFi LAN at around 2.4GHz. The limitation will probably be the CA3130
which is only guaranteed down to 5V but i know it will probably work down to 3 – 4V.
The NE555 can easily be replaced with an LMC555 which will operate down to 1.5V.
The design should also work for the CA3140 op-amp. Is there a low voltage equivalent
that can work equally as well as the 3130/3140?
I have read your extended explanation of how circuit works and was a little bit confused
by the need for the both 5-inch antenna AND the 0.22uF capacitor. I assume the 5-inch
anntenna collects the RF signal (tuned partly by the 22pF caps) and the 0.22uF acts as
a tuned resonator at GHz frequency?
Anyway, thanks once again for publishing your design and allowing people to experiment
with electronics. I am sure you have made one or two enterprising individuals quite wealthy developing this idea into a commercial bug-detector product….. Through e-mail.