|
Footstep Alarm for Human Traffic - This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps. At has an adjustable sensitivity . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006
Fridge-Door Open Alarm - It beeps if the fridge door is left open for too long or hasn't closed properly, to stop food from spoiling. There are lots of other uses as well. __ SiliconChip
Fridge-Door Open Alarm - It beeps if the fridge door is left open for too long or hasn't closed properly, to stop food from spoiling. There are lots of other uses as well. A refrigerator or freezer door that is left open or ajar may cause the food contents to spoil. In some cases, the internal temperature of the fridge or freezer will be maintained if the refrigeration system can cope with the open door __ Learning Electronics
Front Desk Service Beeper - This device functions like a lobby desk service request bell. A short beep is sounded whenever the large pushbutton on top of the device is pressed. Once pressed, the device will not make another beep until at least 2 minutes of time has elapsed . . . Hobby Circuit designed by Dave Johnson P.E.-September, 2005
Game Show Timers - Here is a really simple game show timer designed with the beginner in mind! The power source is an ordinary 12 volt lantern battery or battery pack made up of C or D cells. The lamps may be ordinary flashlight bulbs; the prototype uses 750 mA Krypton types (KPR112) with wires soldered directly onto the bulbs. The control devices __ Contact: Charles Wenzel of Wenzel Associates, Inc.
Generating-5 Volts from a 9 Volt Battery - This is a basic 555 squarewave oscillator used to produce a 1 Khz tone from an 8 ohm speaker. In the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). A small capacitor is used at the transistor __ Designed by Bill Bowden
Harvest Energy using a Piezoelectric Buzzer - 03/20/08 EDN-Design Ideas You can harvest small amounts of mechanical energy using a piezoelectric buzzer to charge a supercapacitor Design by Carlos Cossio, Santander, Spain
Hee HaW Siren - Build the circuit and listen. Change the resistors and capacitors to get all sorts of different results. __ 555-Timer
High Sound Output Beeper - I you need a real loud beeper, this circuit delivers about 110db (12 inches away) from a 9v battery using a single inexpensive C-MOS IC. An off-the-shelf piezoelectric beeping device is driven at resonance to insure maximum efficiency. By changing the control IC to a 74AC14, the same circuit can operate from 3v and 1.5v batteries. . . Circuit by Dave Johnson P.E.-June, 2000
Illuminated 16vAC Doorbell Lamp Replacement - A while back I noticed that the lamp inside the illuminated pushbutton switch for my doorbell burned out. I carefully removed the doorbell, opened the switch housing and then replaced the incandescent lamp inside with the circuit shown below. The circuit uses two small but very bright green LEDs from King Bright. The resistor sets the average LED current at about 3ma. The diode prevents reverse biasing the LEDs. The two lamps emit plenty of light and should last much longer than the incandescent lamp they replaced . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2006
Indicates when it is Time to Dust - I have used the circuit below for many different applications, which require ultra low power drain. It uses a single CA4013 flip/flop. One section forms a pulse generator. The generator produces 100uS pulses at a rate of about 1 per secondCircuit Solution by David A. Johnson P.E.-May, 2006
Inexpensive LED Drives Flash & Beep - 06/05/97 EDN-Design Ideas Sometimes, you need an alarm that is both audible and visible in an application that's stingy with space, power, and budget. The circuit in Figure 1a is compact, efficient, and inexpensive. The F336HD flashing LED (part no.276-036 at Radio Shack) is a useful device. It operates directly from 5V and produces a consistent pulse of light at approximately 1 Hz without a time-constant capacitor. Design by Dennis Eichenberg, Parma Heights, OH
Knocking rings Doorbell - In some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door. The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2009
Kojak Siren - Here is a very simple Kojak siren that is built with two 555 timer ICs and has 2 linear potentiometers that allows the control of sound speed and tone. IC2 produces a sound that can be adjusted with P2 and then drives a small speaker. The amplitude of the signal is modulated by IC1 with a low frequency signal. The modulation __ Designed by Popescu Marian
LED Array powered by 24 VA - C - 24vac is a popular voltage. It is often used in low voltage lighting systems and industrial controls. It is much less dangerous than 120vac/240vac line voltages. This hobby circuit below is one method to efficiently power a cluster of 7 white LEDs from 24vac. . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2009
LED Drives Flash-and-Beep - 06/05/97 EDN-Design Ideas Sometimes, you need an alarm that is both audible and visible in an application that's stingy with space, power, and budget. The circuit in Figure 1a is compact, efficient, and inexpensive. The F336HD flashing LED (part no.276-036 at Radio Shack) is a useful device. It operates directly from 5V and produces a consistent pulse of light at approximately 1 Hz without a time-constant capacitor. Design by Dennis Eichenberg, Parma Heights, OH
Light Activated Siren - This light activated siren could make an unknowing “victim” wet his pants when turning on the lights in a dark room. This thing is LOUD! Power into the module is 3W and produces a 123db sound level from its 50mm diameter diaphragm. It wavers between 2kHZ and 4kHZ. An LDR senses ambient light level and switches on __ Designed by Jim Keith
MEET WAILER-Siren Sound - Our WAILER has many applications; fill your party with wailing sounds! Mount the WAILER on your bicycle so you can make noise while you ride. No need for mechanical rings. Mount it as a front door bell. Or mount it in your room as an alarm. Place WAILER anywhere you’d like to draw attention, to make a neighbor yell, or cause your friends to laugh. The unique small design will allow you to mount it almost anywhere. Operate it with 6V (combination of four series D, AAA or AA size batteries), 9V battery, 12V car battery or via one of our batteries simulator kits. __ Contact: Kit from Elich Industrial Development, Corp
Microcontroller Drives Piezoelectric Buzzer At High Voltage - 03/01/12 EDN-Design Ideas Drive the buzzer directly from the μC’s I/O pins. Piezoelectric buzzers find wide use in embedded systems for audible-signal generation. You can drive a piezoelectric element directly from a microcontroller’s I/O pins, but the maximum voltage rating and loudness of a piezoelectric buzzer are typically several times larger than the voltage an I/O pin supplies. Using four enhancement-mode MOSFETs that connect in an H-bridge configuration, the microcontroller can drive the buzzer at a high alternating voltage. The gate terminals of the N-channel transistors in the lower arms of the bridge can connect directly to the microcontroller’s I/O pins. The voltage level on the I/O pins is insufficient for switching the P-channel transistors, however. Design by Mehmet Efe Ozbek, PhD, Atilim University, Ankara, Turkey
Microcontroller Drives Piezoelectric Buzzer At High Voltage through One Pin - 08/17/12 EDN-Design Ideas If you're short on I/O pins, this circuit might solve your problem. Design by Mehmet Efe Ozbek, PhD, Atilim University, Ankara, Turkey
Multi-Switch Doorbell with Indicators - Here’s the circuit of a multi-switch input musical doorbell (shown in Fig.1). The circuit is built around the popular and less expensive quad D-latch CD4042B (IC1).When switch S6 is pushed to __ Electronics Projects for You
Multi-Tone Configurable Alarm - Presented here is a multi-tone configurable alarm that can be activated by temperature and other physical parameters. Its output tone can be selected through different switch combinations. Such an alarm is __ Electronics Projects for You
Multitone Siren - This multitone siren is useful for burglar alarms, reverse horns, etc. It produces five different audio tones and is much more ear-catching than a single-tone siren. The circuit is built around popular __ Electronics Projects for You
Next-Generation-Star-Trek Doorbell - In the Star Trek “Next Generation” TV series, the doorbell outside the private quarters of a crew member makes a particular “beep-boop” sound. The 3v battery powered circuit below tries to simulate this sound. The circuit uses one 74HCT74 dual D flip/flop . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2001
Novel buzzer using a relay & transformer - This novel buzzer circuit uses a relay in series with a small audio transformer and speaker. When the switch is pressed, the relay will operate via the transformer primary and closed relay contact. As soon as the relay operates the normally closed contact will open, removing power from the relay, the contacts close and the sequence repeats, all very quickly __ Designed by Andy Collison |
