Electronics Assistant

Electronics Assistant

Electronics Assistant is a Windows program that performs electronics-related calculations. It includes a resistor color code calculator, resistance, capacitance and power calculations and more. Details of calculations can be saved or printed. It provides all the functions found in the calculators section of this site and more in a stand-alone user friendly program.


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Resistor Color Code Generator

Resistor Color Code Generator



Screen Shot



Resistor Color Coder is free, and is very useful for determining the color codes or values of 4 and 5 band resistors. To select the mode, click on the 4 or 5 band resistor icon in the upper right corner of the screen. The left hand 3 or 4 bands determine resistor value, the righthand band resistor tolerance.



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Long duration timer circuit

Long duration timer circuit

Description

This timer circuit can be used to switch OFF a particular device after around 35 minutes. The circuit can be used to switch OFF devices like radio, TV, fan, pump etc after a preset time of 35 minutes. Such a circuit can surely save a lot of power.

The circuit is based on quad 2 input CMOS IC 4011 (U1).The resistor R1 and capacitor C1 produces the required long time delay. When push button switch S2 is pressed, capacitor C1 discharges and input of the four NAND gates are pulled to zero. The four shorted outputs of U1 go high and activate the transistor Q1 to drive the relay. The appliance connected via the relay is switched ON. When S2 is released the C1 starts charging and when the voltage at its positive pin becomes equal to ½ the supply voltage the outputs of U1 becomes zero and the transistor is switched OFF. This makes the relay deactivated and the appliance connected via the relay is turned OFF. The timer can be made to stop when required by pressing switch S1.

Circuit diagram

Construction

• Assemble the circuit on a good quality PCB or common board.
  
• The circuit can be powered from a 9V PP3 battery or 12V DC power supply.
  
• The time delay can be varied by varying the values of C1&R1.
  
• The push button switch S2 is for starting the timer and S1 for stopping the time.
  
• The appliance can be connected via contacts N1 & N2 of the relay RL1.
• The IC U1 is 2 input quad NAND gate 4011.

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Load Sensing Power Switch

Introduction:-

This circuit will automatically switch on several mains-powered "slave" loads when a "master" load is turned on. For example, it will switch on the amplifier and CD player in a stereo system when the receiver is turned on. It works by sensing the current draw of the "master" device through a low value high wattage resistor using a comparator. The output of that comparator then switches on the "slave" relay. The circuit can be built into a power bar, extension cord or power center to provide a convenient set of "smart" outlets that switch on when the master appliance is powered (turn on the computer monitor and the computer, printer and other peripherals come on as well).

Diagram:-



click on the image for better quality................

Parts:-

Part	Total Qty.	Description	Substitutions
C1, C3	2	10uF 35V Electrolytic Capacitor
C2	1	1uF 35V Electrolytic Capacitor
R1	1	0.1 Ohm 10W Resistor
R2	1	27K 1/2W Resistor
R3, R4	1	1K 1/4W Resistor
R5	1	470K 1/4W Resistor
R6	1	4.7K 1/2W Resistor
R7	1	10K 1/4W Resistor
D1, D2, D4	3	1N4004 Rectifier Diode
D3	1	1N4744 15V 1 Watt Zener Diode
U1	1	LM358N Dual Op Amp IC
Q1	1	2N3904 NPN Transistor
K1	1	Relay, 12VDC Coil, 120VAC 10A Contacts
S1	1	SPST Switch 120AVC, 10A
MISC	1	Board, Wire, Socket For U1, Case, Mains Plug, Socket

Notes:-

1. This circuit is designed for 120V operation. For 240V operation, resistors R2 and R6 will need to be changed.
2. A maximum of 5A can be used as the master unless the wattage of R1 is increased
3. S1 provides a manual bypass switch.
4. THis circuit is not isolated from the mains supply. Because of this, you must exercise extreme caution when working around the circuit if it is plugged in.

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LASER Power Supply

Diagram:-


click on the image for better quality........................

Parts:-

Part	Total Qty.	Description	Substitutions
R1	1	10 Ohm 10W Or Greater Resistor
R2	1	Ballast Resistor, See "Notes"
D1, D2, D3	3	1N4007 Silicon Diode
C1, C2, C3	3	0.1 uF 2000V Capacitor
T1	1	9V 1A Transformer
S1	1	115V 2A SPST Switch
MISC	1	Case, Wire, Binding Posts (for output), Line Cord

Notes

1. T1 is an ordinary 9V 1A transformer connected backwards for step up.
2. R1 MUST be installed on a LARGE heatsink. A good heatsink is the metal case the supply is built in.
3. R2 Protects the laser tube from excess current. It should be soldered directly to the anode terminal on the tube. To find R2, start with a 500K 10W resistor and work down until the tube lights and remains stable.
4. If you have trouble with the tube not starting easily, use a longer anode lead that is wrapped around the tube.
5. Depending on the transformer you use, the circuit may or may not work. I cannot guarantee the operation of this circuit. Build at your own risk. Some transformers contain very few secondary windings which will quickly saturate the core and basically act like a direct short. The more secondary windings (that is, primary in this circuit) the better.

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Sound Level Meter

introduction:-
This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. This circuit can also be integrated into audio amp projects.

Diagram:-



click on the picture for better view..............

Parts:-

Part	Total Qty.	Description	Substitutions
C1	1	2.2uF 25V Electrolytic Capacitor
C2, C3	1	0.1uF Ceramic Disc Capacitor
R1, R3	2	1K 1/4W Resistor
R2	1	10K 1/4W Resistor
R4	1	100K 1/4W Resistor
R5	1	1M 1/4W Resistor
D1	1	1N914 Silicon Diode
Q1	1	2N3906 PNP Transistor
LED1-LED10	10	Standard LED or LED Array
U1	1	LM3915 Audio Level IC
MISC	1	Board, Wire, Socket For U1

Notes:-

1. V+ can be anywhere from 3V to 20V.
2. The input is designed for standard audio line voltage (1V P-P) and has a maximum input voltage of 1.3V.
3. Pin 9 can be disconnected from +V to make the circuit use a moving dot display instead of a bar graph display.

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call recorder

Introduction:-
circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder's microphone input, and the recorder's remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less.

Diagram:-



click on the image for better quality..................

Parts:-

Part	Total Qty.	Description	Substitutions
R1	1	270K 1/4 W Resistor
R2	1	1.5K 1/4 W Resistor
R3	1	68K 1/4 W Resistor
R4	1	33K 1/4 W Resistor
C1	1	0.22uF 150 Volt Capacitor
Q1, Q2	2	2N4954 NPN Transistor
D1	1	1N645 Diode
MISC	1	Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug

Notes:-

1. The circuit can be placed anywhere on the phone line, even inside a phone.
2. Some countries or states require you to notify anyone you are talking to that the conversation is being recorded. Most recoders do this with a beep-beep. Also, you may have to get permission from the phone company before you connect anything to their lines.

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Remote Telephone Ringer

Introduction:-
This remote telephone bell ringer allows you to use a large (and loud) external bell in place or in addition to the built in (and rather wussy) ringer in most modern telephones. This is ideal for large outdoor areas, noisy shops or those hard of hearing. Most any large bell can be used as the circuit can be easily adjusted for various supply voltages.

Diagram:-



click on the image for better quality......................

Parts:-

Part	Total Qty.	Description	Substitutions
C1	1	0.47 300V Capacitor
C2	1	47uF 25V Electrolytic Capacitor
R1	1	1K 1/4W Resistor
R2	1	10K 1/4W Resistor
R3	1	1K Pot
R4	1	2K 1/4W Resistor
Q1	1	6A, 200V TRIAC
Q2	1	6A, 200V SCR (106, Etc.)
D1	1	1N4774 Zener Diode
D2, D3	2	1N4007 Rectifier Diode
U1	1	4N33 Opto Isolator
BELL	1	Large Bell (Fire Bell, School Bell, Etc.)
MISC	1	Board, Wire, Socket For U1, Case

Notes

1. Virtually any TRIAC and SCR will work for Q1 and Q2 as long as the voltage rating is high enough. Q2 needs enough current capacity to handle the full load of the bell.
2. To adjust R3, call the phone line on which the ringer is installed and adjust the pot until the bell begins to sound consistently.
3. Make sure to check with local authorities before you connect a homemade device to your phone lines. Some areas mandate that only approved devices can be connected to the loop. This circuit provides an opto-isolator to prevent cosstalk between the phone line and power supply as well as to avoid ground loops.

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Aircraft Radio Communications Receiver

Introduction:-
The communications between commercial aircraft and the ground can be interesting, amusing and sometimes even disturbing. However radios that receive the approximately 220MHz to 400MHz band commonly used for aircraft (both military and commercial) are not easily found. And scanners can be complicated, large and expensive. With an easy to build circuit such as this one, everyone can enjoy listening in on these conversations.

Circuit diagram:-



click on the picture for better quality................

Parts:-

Part	Total Qty.	Description	Substitutions
R1, R3	2	47K 1/4W Resistor
R2	1	10K 1/4W Resistor
R4	1	4.7K 1/4W Resistor
R5	1	5K Linear Taper Pot
R6	1	2.2K 1/4W Resistor
C1, C2, C3, C6	4	0.001uF Ceramic Disc Capacitor
C4	1	2.2pF Ceramic Disc Capacitor
C5	1	1pF Ceramic Disc Capacitor
C7	1	15uF 15V Electrolytic Capacitor
C8	1	18pF Variable Capacitor
D1	1	1N82 Diode
Q1	1	2N918 NPN Transistor
L1	1	See Notes
L2	1	1.8uH Inductor
ANT1	1	Approx. 18 Inch Wire Antenna
MISC	1	PC Board, Wire, Knob For C8

Notes:-

1. L1 is made by winding 2 turns of 22 AWG magnet wire on a 5/32 drill bit. This inductor can be modified to shift the frequency range of the circuit.
2. The antenna can also be placed at the anode of D1 if overload is a problem with it connected to the emitter of Q1
3. R5 adjusts regen and thus sensitivity.

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Crystal Radio

Introduction:-
The circuit is very simple with only 5 parts, but performs very nicely when used with the right size antenna.

Diagram:-



click on the image for better view...................

Parts:-

Part	Total Qty.	Description	Substitutions
C1	1	Tuning Capacitor (See Notes)
D1	1	1N34 Germanium Diode
L1	1	Loopstick Antenna (See Notes)
SPKR1	1	Crystal Earphone
MISC	1	Wire, Board, Wire For Antenna, Knob For C1

Notes:-

1. C1 and L1 can be bought, or salvaged from an old AM radio (which is where I got mine). You may need to experiment with the connections on L1 in order to get the best (or any) signal.
2. You may or may not need the ground connection. I never use it and the radio usually works fine without it.
3. The bigger the antenna, the more stations you pick up and the louder you hear them. On my radio, I get about 10 stations, 3 of which are very loud in the earphone. Of course, not everyone has room for a 60' antenna...
4. A 47K resistor in parallel with the earphone will help properly load the detector

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Horn Beep Canceller

DEFINITION:-
It's a great convenience that most modern cars come with a built in alarm, however it is nothing but noise pollution that the horn sounds when the alarm is armed. Disconnecting the alarm system from the horn relay will eliminate this, but prevent the horn from sounding in the even of an actual alarm. This circuit serves to silence the arming beep yet maintain the alarm by introducing a small delay into the signal. It sits between the alarm and horn relay. The alarm must provide a constant horn signal for at least 3 seconds before the horn relay is activated. That way the quick "beep" will never activate the horn relay, while the constant alarm signal will.

Diagram:-




Components required:-

Part	Total Qty.	Description	Substitutions
C1	1	0.01uF Ceramic Disc Capacitor
C2	1	100uF 35V Electrolytic Capacitor
R1	1	1K 1/4W Resistor
R2	1	10K 1/4W Resistor
R3	1	15K 1/4W Resistor
R4	1	470 Ohm 1/4W Resistor
D1, D3, D4	3	1N4004 Rectifier Diode
D2	1	Red LED
U1	1	555 Timer IC
K1	1	SPST 12V Automotive Relay
MISC	1	Board, Wire, Socket For U1, Case

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