[ultrasonic mosquitoes repeller]

I tried about the same transistorised circuit a few years ago. It worked successfully for a day or two & then mosquetos got used to it :o. What the hell i tweaked the RC values to change the frequency (by how much i don't know :() but no avail. Hope it works for you. ;D

[The LM317 Calculator]

Thanks, audioguru & MP
but u missed the point. Well i learned elementry maths early in life & can do it well (i belive ;D). But i like to rest my brain once a while & let the computer do the dumb stuff. Thanks for the LM117 & LM317 tip uptill now i almost always used 220E. But then i was not arguing aout LM317 but this was just a suggesion to improve the calc since it is already there & there is no user feedback link.

[The LM317 Calculator]

I liked the LM317 calculator on this site (http://www.electronics-lab.com/articles/LM317/index.html). But i have one suggestion - please make it calculate one resistor frem the o/p voltage and other resistor coz usually that is needed. ;D

[Inside a TO-3 Transistor case]

I used the SL100 with it's top chopped off as a phototransistor (2N3055 was too heavy for my hacksaw then ;)). It gave good response indeed. But beware you have to cover it with some material to keep the dust off else it will die slowly. ;D

[Notch Filters and Noise Cancellers]

Put that notch filter afer the pre-amplifier. i.e. just before the volume control. Are you sure it's 120Hz buzz? It seems more like a RF interference.

[regulated 12 v dc and 500 mA current o/p]

what do you want constant current or constant voltage? http://www.electronics-lab.com/projects/power/008/index.html i think this should help if you need constant voltage. but 7812 will do a better job.

[Adams Motor Project]

Voltage increse is ok but what about the direction of current is it going inside the battery?

[Infra Red Remote control]

check this out
http://www.wimb.net/index.php?s=electr&page=7

[remote control using radio freq]

Check this out remove the IR parts & place RF communication link it might just work ;D
http://www.wimb.net/index.php?s=electr&page=7

[How Hard to Use Floppy For Flasher?]

Not worth the trouble ;D. Most systems based on microcontrollers are meant to be small & inexpensive. Interfacing a floppy drive would take extra hardware on board. If you want portability you should try using a flashcard / USB stick. Anyway that's my view :)

[What Chip Converts Decimal to Pulse ..?]

A microontroller & a few lines of code will be sufficient here. Unless you require very small pulse duration. A digital circuit may also be build by using counters & gate but cost will be higher than microcontroller solution.

[I need help with my project...]

You obiviously need an RTC here to keep track of the current time (DS1307 is the simplest). LCD & keypad or a serial link may be used to set the current time. A microcontroller for keeping things in control (PIC or 89C51 take your pick).

[12v lamp Dimmer lamp ideas?]

I know this is an overkill ;D but check this IC out http://www.alldatasheet.co.kr/datasheet-pdf/pdf_kor/LSI/LS7631.html

[single phase controlled rectifier for DC motor]

Hope this helps this document dose not gives direct DC voltage => Motor Speed circuit but has potentiometer controlled circuits. http://www.littelfuse.com/data/Application_Notes/an1003.pdf

[Protel DXP PCB Question]

I think Protel DXP provides an autoplace option but it's not very easy to use. However there is a software dedicated to auto placement check it out http://www.eda.co.uk/actiplace.html.

[Protel DXP PCB Question]

Rules posted by trigger help a lot indeed but it's the practice that makes man perfect. so keep changing the layout and take brakes wen you get bored. :)
Don't be afred of freqquent changing the layout more time you put into this now less time you will have to spend later

[Computer Project - Grounding Question]

You should not connect signal ground to the chassis for a mains connected equipment. There is a seperate Earthing lead in mains supply for it. Just design your PCB right & you won't have trouble of interferance unless you are in industrial envoryment.

[call timer for mobile phones]

I found this while searching might be helpful http://www.techlib.com/electronics/cellhelp.htm

[TTL 74AS IC]

if u want really small quantity (5-6 pcs.) u can order samples from TI itself! U can expect them delivered within a week! ;)

[Help me about a PC Osciloscope]

You have to build an attenuator for scaling the input signal. Even then your bandwidth wil be limited to about 20KHz (i.e. AF range). If that is not sufficient, then you have to use a fast ADC with FIFO to store the samples then use Serial/Parallel/USB port to upload data to PC & write a program to analyze & display it! Also u may need a frequency synthesizer to generate various sampling rates such that you can measure a signal without overflowing buffer.
you can also take a look at http://www.bitscope.com and analyze their design

[pwm in simulik]

I think u can not write a transfer function for a PWM block. But u can create one easily. Create a counter which runs perpetually. (In the diagram i have not limited it's output but it is essential or u will get very large pulse width ;) )Then compare it's output with incoming signal thats all!

[College textbook question]

Q = C * V
thus,
V = Q / C = 1u / 1u = 1 V
& According to Mr. Ohm
I in resistor = 1 / 10 = 100mA