Circuit Diagram

Voltage Comparator

Published:2012/11/29 0:32:00 Author:muriel | Keyword: Voltage Comparator

This circuit will provide an indication whenever the input voltage differs from two defined limits, V1 and V2. The limits are adjustable and the circuit made to trigger from the adjustable window .   (View)

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Sound Operated Switch

Published:2012/11/29 0:31:00 Author:muriel | Keyword: Sound Operated Switch

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Electronic Night Light

Published:2012/11/29 0:30:00 Author:muriel | Keyword: Electronic Night Light

This circuit for an electronic night light was submitted by Adam from Canada. I have provided the notes.   (View)

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Digital Combination Lock

Published:2012/11/29 0:29:00 Author:muriel | Keyword: Digital Combination Lock

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Electronic Doorbell with Counter

Published:2012/11/29 0:29:00 Author:muriel | Keyword: Electronic Doorbell, Counter

This circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a ding-dong chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors.   (View)

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Doorbell Warning Switch

Published:2012/11/29 0:28:00 Author:muriel | Keyword: Doorbell Warning Switch

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Switch De-Bouncer circuit

Published:2012/11/29 0:27:00 Author:muriel | Keyword: Switch De-Bouncer circuit

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DC Motor Control

Published:2012/11/29 0:26:00 Author:muriel | Keyword: DC Motor Control

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Light Detector Circuit

Published:2012/11/29 0:26:00 Author:muriel | Keyword: Light Detector Circuit

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Electronic Door Release

Published:2012/11/29 0:25:00 Author:muriel | Keyword: Electronic Door Release

The IC is a quad 2 input AND gate, a CMOS 4081. These gates only produce a HIGH output, when BOTH the inputs are HIGH. When the key wired to 'E' is pressed, current through R1 and D1 switchs Q5 on.The relay energises; and Q5 is 'latched on' by R8. Thus, the Alarm is set by pressing a single key,say one of the two non-numeric symbols.   (View)

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Dark Activated Switch

Published:2012/11/29 0:24:00 Author:muriel | Keyword: Dark Activated Switch

This circuit will activate a relay when light falls to a preset level. Light level can be adjusted with VR1 and the relay contacts may be used to operate an external light or buzzer.   (View)

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Frost Alarm

Published:2012/11/29 0:24:00 Author:muriel | Keyword: Frost Alarm

A simple thermistor triggered switch with adjustable threshold. It triggers with cold temperatures so may be used as a frost alarm or cold temperature switch.   (View)

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Building an Adjustable Constant Current Load

Published:2012/11/29 0:22:00 Author:muriel | Keyword: Adjustable, Constant Current Load

Constant current dummy load designs built around the venerable LM324 quad OPAMP have become quite popular in the hobbyist community ever since David Jones at the eevblog popularized the concept in one of his excellent videos. The basic concept has been around for a long time though, and it's essentially an OPAMP based current source design. The current source portion of thecircuit below is very similar to Dave's design. It always bothered me though that the original design didn't use the four OPAMPs in the LM324, and that there was limited protection in the circuit. Therefore, I decided to use one of the two spare OPAMPs for thermal overload protection and another to activate a cooling fan. This approach should result in a more reliable design which is an important consideration for test equipment. Figure 1 shows the circuit schematic. The Current Source portion should be familiar to anyone that has seen similar designs on the web. The U2D OPAMP is a voltage follower that ensures the voltage at the 0.1 Ohm resistor follows the voltage applied to its non-inverting input. Therefore the current at the output through the 0.1 Oh resistor is I = Vi / (0.1) = 10 x Vi. I decided to use a 0.1 Ohm resistor (instead of the common 1 Ohm design)to allow larger currents. The smaller resistor value reduces the power dissipated in the resistor for a given output current. Furthermore, the source-to-ground voltage is also reduced thus ensuring that VGS is kept well above the MOSFET's threshold voltage for all practical operation conditions. I used two 50N06 N-channel MOSFETs in parallel to reduce the total Ron and improve reliability. In this design, the maximum current should be about 7A and it is limited by the 5W resistor I used; not by the MOSFETs. Larger currents can be achieved with a resistor capable of 10 or 20 W dissipation (which I didn't have handy). The input voltage should not exceed 60V (maximum VDS for these MOSFETs). As an added protection measure, I added a power MOV from the input to ground to protect the MOSFETs against high-voltage transients.   (View)

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Constant Current Electronic Power Supply

Published:2012/11/29 0:21:00 Author:muriel | Keyword: Constant Current, Electronic Power Supply

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Solar Battery Charger

Published:2012/11/29 0:20:00 Author:muriel | Keyword: Solar Battery, Charger

A solar battery charger that uses a shunt regulator to prevent overcharging. Circuit uses a 12V solar battery, but can be adapted for other voltages.   (View)

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Under Voltage Circuit

Published:2012/11/29 0:19:00 Author:muriel | Keyword: Under Voltage Circuit

This under voltage circuit may be used as an add-on to an existing power supply or standalone. The circuit draws power from an existing power supply, which may be up to 36 Vdc. Once voltage drops below a preset level the output swings high. A CA3140 MOSFET op-amp is used as a comparator, the output can drive loads of up to 10mA so can drive a low current LED directly. Additional buffering is required for higher loads.   (View)

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EMI Mains Filter

Published:2012/11/29 0:18:00 Author:muriel | Keyword: EMI , Mains Filter

Modern society reliance on electrically driven appliances, creates Electro-Magnetic Interference (EMI) which manifests as electrosmog , a gathering phenomenon to which susceptible people are becoming unusually allergic as recently reported in the press. This is prevalent from power lines, transmitters, electrical and electronic devices, plus data hash from computers in industry, shops, the home and is unavoidably all around us.   (View)

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Radio Friendly Power Supply

Published:2012/11/26 1:08:00 Author:muriel | Keyword: Radio Friendly , Power Supply

Power supplies should not create any unwanted interference across the radio spectrum. Switch mode power supplies are one of the strongest sources of interference, and harmonics can be heard throughout long, medium and short wave bands. This power supply, is extremely noise free, and therefore radio friendly. In addition, it has a very high rejection of line frequency and is suitable for powering receivers and small power transmitters.   (View)

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1.5 to 37 Volt 30 Amp Power Supply

Published:2012/11/26 1:07:00 Author:muriel | Keyword: 1.5 to 37 Volt , 30 Amp, Power Supply

A modification to the 12V 30 Amp power supply. This version uses an LM317 to provide a variable 1.5 to 37 Volt regulated output with currents up to 30 Amps. Max has built his power supply into an old computer case and can be seen on YouTube under Project Icarus.   (View)

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Power Zener Circuit

Published:2012/11/26 1:06:00 Author:muriel | Keyword: Power Zener Circuit

In this circuit a zener diode is amplified by a set of power transistors. The transistors substantially increase the current and power to the load.   (View)

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