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Circuit Solutions Notebook
Last Updated On:  Wednesday June 02, 2021

Latest Technical Challenge           Previous Circuits Solutions

Solutions in Progress

The following are rough ideas that came from website visitors, from my own needs or purely from my imagination.
  1. 60Hz Distortion Meter:   Design a simple circuit, which can display the total harmonic distortion of the sine wave on a standard power line.
  2. 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. 
  3. 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.
  4. 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.
  5. 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. 
  6. 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.
  7. 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.
  8. DC Motor Brake  Design a simple circuit that would automatically apply an electrical brake to the motor, when DC power is removed.
  9. 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.
  10. Earth Ground Signal Monitor:  Could two metal probes stuck in the ground detect footsteps or some other interesting signals?
  11. 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.   
  12. Electrodeless Conductivity Monitor:   Devise a method to monitor the conductivity of a water based fluid without exposed electrodes.
  13. Electrodeless PH Meter:   Is it possible to design a system, which measures the PH of a fluid, without any exposed electrodes?
  14. 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?
  15. 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.
  16. Fanny Detector For a Computerized Musical Chair Game:  Design a low power circuit, which can detect the fanny of people setting in the chairs.
  17. 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 footsteps. 
  18. Freeze AlarmDevise a low power system that will sound an alarm inside a house, when the outside temperature is below freezing.
  19. Freezer Under Temperature Alarm:   Design a low power circuit which will sound an alarm, when the inside temperature of a freezer is above freezing.
  20. Geophone Footstep Alarm: Can a battery powered circuit using surplus geophones be designed that can detect human traffic up to 100 feet away?
  21. 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?
  22. 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.
  23. Hidden Behind Wall Capacitance Switch:   Design a capacitance activated switch, which can be activated by a hand behind a wall.
  24. Human Detection Using Big Mirror:  Can a full-length dressing mirror be used to detect a human moving by?
  25. Human Motion Detection Using Electric Field Changes: Can changes in the earth’s natural electric field be used to detect human motion? 
  26. 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.
  27. 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.
  28. Long Range Driveway Announciator:  Can a laser pointer be used to detect a vehicle entering a driveway, from 1000 feet away?
  29. Long Range Light Beam Intrusion Alarm:   Devise a method to detect human traffic moving through a light beam several miles long.
  30. Long Range Opacity Monitor: Can a system be designed to monitor the clarity of air over a distance of one mile?
  31. 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?
  32. MHD Flow Meter:   Would it be possible to use magneto hydrodynamic methods to measure the flow of seawater through a pipe? 
  33. 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.
  34. 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.
  35. Multi-LED Night Light:  Design a night light, using up to 30 white LEDs.
  36. Office Cubical Entry Indicator:   Design a simple battery powered device that would activate a beeper, whenever someone entered an office cubical.
  37. 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. 
  38. 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.
  39. Optical Fiber Coupled Scope Probe:   Design a system, which can link an oscilloscope to an isolated probe some 100 feet away.
  40. 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 ceilings.
  41. Optical Through the Air Ethernet:   Devise a system that can link two buildings, separated by 1000 feet, with Ethernet communications, using optical methods.
  42. 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.
  43. 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.
  44. Plastic Water Pipe Tracer:   How do you find out the location of sprinkler pipes buried underground?
  45. 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.
  46. 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.
  47. Power Line Noise Indicator:   Design a simple device that indicates the amount of high frequency noise that is on a power line.
  48. 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.
  49. Precision Medical Syringe Volume Monitor:   Devise a method to accurately measure the volume of water based fluid inside a 10cc syringe.
  50. Rain Detector:  Design a rain detector, which is not activated by the fluid but actually detects the falling water drops.
  51. 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?
  52. 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.
  53. 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.
  54. 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.
  55. Short Range Opacity Monitor:   Design a device that monitors how clear the air is over a distance of 10 feet.
  56. Simple Portable Radiation Detector:  Devise a small and simple battery powered device that could detect gamma radiation.
  57. Simple Vehicle Speed Trap:   Can a couple cheap visible red laser pointers be used to measure the speed of vehicle?
  58. 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.
  59. 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.
  60. Snow Depth Alarm  Design a system that would alert a snowplow driver when the snow depth has exceeded four inches.
  61. 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?
  62. Solar Insolation Monitor Design a circuit, which will monitor the sunlight intensity in watts per square foot.
  63. Time to Dust Indicator:   Design a battery powered device, which will alert when it is time to remove dust from the surfaces.
  64. Toilet Flush Counter:   Design a simple system, which can count the number of times a home toilet is flushed each day, week or month.
  65. 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?  
  66. 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.
  67. 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 voltages.

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