Circuit Solutions Notebook
Last Updated On:
Wednesday June 02, 2021
Latest Technical Challenge
Previous Circuits Solutions
Solutions in Progress
following are rough ideas that came from website visitors, from my own needs or purely from my
- 60Hz Distortion Meter:
Design a simple circuit, which can display
the total harmonic distortion of the sine wave on a standard power line.
- Automatic Convenience Store 911 Caller:
Would it be possible to monitor a store clerk’s heart rate and automatically call 911 when
the heart rate suddenly jumped? The sudden rate change would be triggered by a robbery or
some very stressful situation.
- Battery Amp-hour Tester:
Design a circuit, which can measure a
battery’s amp-hour rating, using either a constant resistance or a constant current load.
Equip the circuit with an automatic voltage cut-off.
- Battery Free Roadside Barrier Flasher:
Design a system that would turn on a bright roadside barrier type flasher. Use super
bright white LEDs, a small solar panel and super capacitors.
- Battery Free Walkway Lights:
Design a walkway light that uses a super
capacitor instead of a battery to store energy from a small solar panel and use that energy
to light a LED or two at night.
- City Water Tower Ladder Alarm:
Devise a method to detect when a human is
climbing on the ladder of a water tower. The device must be free of false alarms due to
wind, snow, rain and birds.
- Communications Through Cement Walls:
Can an inductive method be used to send
data through a cement wall? This might be helpful for linking some sensors positioned
outside of a house to the inside, without wires and without conventional RF methods.
DC Motor Brake:
Design a simple circuit that would automatically apply an electrical brake
to the motor, when DC power is removed.
- DC to DC Converter for Single 0.5v Solar Cell:
Design a circuit, which can convert 0.5 volts from a single solar cell to say 6 volts.
- Earth Ground Signal Monitor:
Could two metal probes stuck in the ground
detect footsteps or some other interesting signals?
- Earthquake Alarm:
Can a battery powered circuit be designed
that it would sound an alarm when the building shakes? The device might give the owner a few
extra seconds to seek shelter.
- Electrodeless Conductivity Monitor:
Devise a method to monitor the conductivity of a water based fluid without exposed
- Electrodeless PH Meter:
Is it possible to design a system, which
measures the PH of a fluid, without any exposed electrodes?
- Electronic Delay Circuit for VOX Microphones:
Can an bucket brigade analog delay devices be used to prevent the clipped first syllable of
the first word spoken?
- Explosive Detection Using Optical Fluorescence Methods:
Explore methods of detecting explosives using newly discovered optical techniques, which
looks for the 705 nanometer signature of explosives, illuminated with green laser light.
- Fanny Detector For a Computerized Musical Chair Game:
Design a low power circuit, which can detect the fanny of people setting in the chairs.
- Footstep Monitor Using an Optical Fiber:
Devise a circuit, which uses a single
length of plastic or glass optical fiber to detect the vibrations associates with human
Freeze Alarm: Devise a low power system that will sound an alarm inside a house, when the outside
temperature is below freezing.
Freezer Under Temperature Alarm: Design a low power circuit which will sound an alarm, when the
inside temperature of a freezer is above freezing.
- Geophone Footstep Alarm:
Can a battery powered circuit using surplus geophones be designed that can detect human
traffic up to 100 feet away?
- Grocery Store LED Sale Flasher Without Batteries:
Could a small solar cell and a supper capacitor be used to keep a device
flashing, drawing energy from the lights within the store?
- Hallway Human Entry Announciator:
Design a circuit, which can be hidden inside a picture frame, which would activate a sound
maker, whenever a human would walk by the device.
- Hidden Behind Wall Capacitance Switch:
Design a capacitance activated switch, which can be activated by a hand behind a wall.
- Human Detection Using Big Mirror:
Can a full-length dressing mirror be used to detect a human moving by?
- Human Motion Detection Using Electric Field Changes:
Can changes in the earth’s natural
electric field be used to detect human motion?
- Is the Tube Filled with Clear Liquid or Not?:
Devise a circuit that can determine if a
one inch diameter piece of clear tubing has alcohol in it or not.
- Jeopardy Game Boxes:
Design a system for a Jeopardy style game to be used in classrooms, which does not require
any wires and is confined to only one classroom.
- Long Range Driveway Announciator:
Can a laser pointer be used to detect a
vehicle entering a driveway, from 1000 feet away?
- Long Range Light Beam Intrusion Alarm:
Devise a method to detect human traffic
moving through a light beam several miles long.
- Long Range Opacity Monitor:
Can a system be designed to monitor the
clarity of air over a distance of one mile?
- Long Range Optical Radar Using Nitrogen Sparks:
Can the small but very bright light from a simple spark gap be used to form a long range
optical radar system?
- MHD Flow Meter:
Would it be possible to use magneto
hydrodynamic methods to measure the flow of seawater through a pipe?
Miniature Lighthouse Light Simulator: Design a circuit for HO trains models, which flashes an LED in a
manner that duplicates the light from a lighthouse.
- Miniature Low Power AC to DC Power Supply: Design a
miniature circuit, which can convert 120vac to +5 volts at a current of 100 milliamps, with
full 5KV isolation.
Multi-LED Night Light:
Design a night light, using up to 30 white LEDs.
- Office Cubical Entry Indicator:
Design a simple battery powered device
that would activate a beeper, whenever someone entered an office cubical.
- Open Radio Transmitter Tower Lamp Indicator:
Design a simple circuit that will light and LED light when the circuit does not detect the
current to the tower lamp.
- Optical Fiber Coupled DVM Probe:
Devise a system that can use an optical fiber to link a probe to a standard DVM over a
distance of 100 feet.
- Optical Fiber Coupled Scope Probe:
Design a system, which can link an
oscilloscope to an isolated probe some 100 feet away.
- Optical ID Badge Transmitter:
Could an optical method be used to detect
and ID the location of people within a building? Perhaps detectors would be located on the
- Optical Through the Air Ethernet:
Devise a system that can link two
buildings, separated by 1000 feet, with Ethernet communications, using optical methods.
- Phone Booth Occupancy Light Switch:
Devise a circuit, which can turn on the
light inside a phone booth, whenever a human is inside the booth.
- Pigeon Scaring Device, Electronic Scarecrow:
Devise a battery powered system that could be mounted on top of a roof, which would detect
and shoo away pigeons.
- Plastic Water Pipe Tracer:
How do you find out the location of sprinkler pipes buried underground?
- Portable Solar Power Vest and Hat:
Devise a vest studded with solar cells and a broad brim hat, which can supply power to
portable tools or camcorders.
- Portable Traffic Counter:
Devise a simple method to count the number of vehicles passing a point on a road. The
system must be unobtrusive and easy to install.
- Power Line Noise Indicator:
Design a simple device that indicates the amount of high frequency noise that is on a power
- Precision 10 Amp AC Current Source:
Design a circuit, which can route a very
clean 60 hertz sine wave signal through a low resistance load, while maintaining an accurate
10 amps of current. The waveform needs to be very clean and free of harmonics.
- Precision Medical Syringe Volume Monitor:
Devise a method to accurately measure the
volume of water based fluid inside a 10cc syringe.
- Rain Detector: Design a rain detector, which is not activated by the fluid
but actually detects the falling water drops.
- Remote On/Off Control Using Xenon Flash Light Source:
Can a long range remote Controller be designed so light from a xenon flash can turn
something on and off?
- Sensitive Average Current Meter:
Design a circuit, which can measure the
average current drawn by a circuit, which may draw current in pulses of 50 milliamps for a
few milliseconds, every few seconds.
- Short Range Audio Link Using Magnetic Bubble Methods:
Experiment with some inductive approaches that can send audio information from a transmitter
to a receiver, over a range of six feet.
- Short Range Hand Wave Detector:
Design a battery powered circuit, which can turn something on or off, with the wave of a
hand over the device.
- Short Range Opacity Monitor:
Design a device that monitors how clear the air is over a distance of 10 feet.
- Simple Portable Radiation Detector:
Devise a small and simple battery powered device that could detect gamma radiation.
- Simple Vehicle Speed Trap:
Can a couple cheap visible red laser pointers be used to measure the speed of vehicle?
- Small Motor Speed and Torque Controller:
Design a circuit, which can control the speed and maximum torque of a small
DC motor. Use a method that does not require any special encoders on the motor.
- Snap Spring Powered RF Transmitter for Garage Door Opener:
Devise a way to use the energy in the compression of a spring, to supply power a low power
RF transmitter, which would operate a garage door opener. Such a device would then not
ever require a battery.
Snow Depth Alarm:
Design a system that would alert a snowplow driver when the snow depth has
exceeded four inches.
- Soil Moisture Monitor Using Electrodeless Techniques:
Is it possible to use some magnetic induction methods to measure the conductivity of the
soil underground and use that information to determine if the soil needs more water?
Solar Insolation Monitor:
Design a circuit, which will monitor the sunlight intensity in watts per square foot.
Time to Dust Indicator:
Design a battery powered device, which will alert when it is time to remove
dust from the surfaces.
- Toilet Flush Counter:
Design a simple system, which can count
the number of times a home toilet is flushed each day, week or month.
Ultra Low Power Human Finger Detector:
Could a slotted or reflective optical
sensors be used in an ultra low power circuit to detect a human finger?
Ultra Low Power Latching Relay Circuit: Design a circuit, which can latch and unlatch +5v latching
relay from a small 3 volt lithium cell battery.
Voltage Booster for Wall Mounted Power Adapter:
Design a circuit that will give a marginal
AC to DC linear power supply a voltage boost, so it can maintain regulation at low line