| |
Circuits of the Week
Last Updated on:
04/27/2008 06:17 AM
(Dec 2007 - July 2007)
(June 2007 - Jan 2007)
(Dec 2006 - July
2006)
(June 2006 - Jan 2006)
(Dec 2005 - May 2005) |
| Dec 31, 2006 |
Check Engine Beeper
When wired into a car’s indicator light panel, this circuit will turn on a loud beeper when the “check engine” light turns on. |
| Dec 24, 2006 |
40KHz Limiting Amp
This circuit has a gain of X20 at 40KHz. The amplifier output level is limited to 2.5v peak to peak. Limiting action begins with a 50v peak to peak input.
Merry Christmas |
| Dec 17, 2006 |
Audio Signal Detector Switch
This circuit will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal. It could be used to turn on a relay, routing the signal to were it is needed.
Happy Birthday, Dave |
| Dec 10, 2006 |
Precision 40KHz Triangle Generator
This circuit generates a precision 40KHz triangle waveform. |
| Dec 3, 2006 |
Thermocouple Temperature Activates Relay
Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F. |
| Nov 26, 2006 |
Medium Power 40KHz Ultrasound Transducer Driver
This crystal controlled circuit drives a 40KHz piezoelectric transducer with a 30v peak to peak signal. |
| Nov 22, 2006 |
Dark Activated 12v Power Supply Switch
Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down. |
| Nov 12, 2006 |
Modulated Light Monitor
This battery powered circuit will work from DC to 500KHz. It is designed to connect to an oscilloscope to monitor the light level changes and modulated signals. |
| Nov 5, 2006 |
AC Line Powered LED Pilot Light
This simple circuit can be used to light a LED indicator lamp, powered from the 120vac line. I have included component values for 240vac lines as well. |
| Oct 29, 2006 |
Home Made Geophone Detects Foot Stomp
A home made geophone is made from a strong magnet, a coil of wire and a rubber band. The circuit is sensitive enough to detect the vibrations of a nearby foot stomp. It could be used as an
earthquake detector. (added 7/06) |
| Oct 22, 2006 |
12v Light/Dark Lamp Switch
At night, this circuit will route current to a 12v lamp, turning it on. |
| Oct 15, 2006 |
12v Lamp Current Indicator
This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp. |
| Oct 8, 2006 |
Pushbutton Activated Service Request Beeper
A single press of a pushbutton switch turns on a beeper for one second but can’t be activated again for 60 seconds. |
| Oct 1, 2006 |
Solar PV cell Test Fixture
This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current. Using a PIN photo diode and a control circuit, the solar cells can be
tested under constant light level conditions. A halogen incandescent lamp is used as the light source. |
| Sept 24, 2006 |
Reflected Infrared Light Switch
Infrared light reflected off a finger is used to activate this switch circuit. |
| Sept 17, 2006 |
2.45GHz RF Signal Detector
This passive RF indicator is made from a few simple parts. A 100uA moving coil meter is used to display the relative intensity of the RF signal. This circuit can be used with some cell
phones and many cordless telephones. |
| Sept 10, 2006 |
Incandescent Lamp Inrush Current Limiter
This circuit limits the large inrush current often associated with large incandescent lamps. With the components shown the current is limited to 1 amp, but it could be scaled to any desired
current. |
| Sept 3, 2006 |
12v Light/Dark Lamp Switch
At night, this circuit will route current to a 12v lamp, turning it on. |
| Aug 27, 2006 |
Piezoelectric Vibration Sensor Activates Switch
An inexpensive piezoelectric wafer is used to detect vibration and when the vibration is sufficient a switch is activated. |
| Aug 20, 2006 |
Piezoelectric Triggered Switch
Two different switch circuits are shown. One sources current and the second sinks current. Both switches are connected to a piezoelectric wafer. When the wafer is tapped, the
switches are activated. |
| Aug 13, 2006 |
Low Voltage Latching Relay Driver
Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source. By using a latching relay, power can be
controlled to a load with a tiny battery. |
| Aug 6, 2006 |
Electrodeless Water Level Monitor
This system operates much like a classic float switch but without any moving parts. The illustration shows how a system using two copper coils sealed inside a plastic pipe, can detect the level
of water outside the pipe. Whenever the water level is lower than the upper coil, no signal is coupled between the coils. Once calibrated, this technique might also work on the outside
of a plastic water tank. |
| July 30, 2006 |
125KHz Wireless Smart Key Detector
This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip. (added 7/06) |
| July 23, 2006 |
Battery Charge Current Indicator
This circuit turns on a LED whenever it detects at least 25ma of battery charge current. (added 7/06) |
| July 16, 2006 |
40KHz Ultrasound Receiver
A X100 transistor amplifier is followed by a zero cross detector circuit, using a voltage comparator. The output is a TTL logic signal, corresponding to the received 40KHz signal. (added
7/06) |
| July 9, 2006 |
9v Battery Voltage Monitor
This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also contains a 1.18v reference
diode. In standby mode, the circuit draws only 4uA. (added 7/06) |
| July 2, 2006 |
0.5V Negative Supply
Although not very efficient, this simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps. It is ideal for supplying
a negative rail to low power “rail to rail” op amp circuits, which need to have a true zero volts output. |
| |
(Dec 2007 - July 2007)
(June 2007 - Jan 2007)
(Dec 2006 - July
2006)
(June 2006 - Jan 2006)
(Dec 2005 - May 2005) |
