Electronics Forum / Electronics / April 2005

I am requesting help to construct an ultrasonic device that emits sound at
about 25Khz.  Unlike most ultrasonic devices, I want the device to carry
sound over 100 feet (or 30 meters) and still be over 140 decibels at 100
feet (or 30 meters).

I heard on tv that public electricity supply was originally D.C.
 Why did they send D.C. down the wires instead of A.C.?
I thought that elctricity is generated as A.C. in spinning
generators, and has to be converted to D.C.

Dear Madam/Sir,
You are invited to participate in an international research study.
This research project is headed and led by Cambridge student Nico
Baumgarten.  http://crosscultural.research.gotdns.org

Can anyone suggest such a device, and where I can buy just a couple of
them?  The only sensor I've found locally at a retail level is the
analogue UGN3503U, at Jaycar.
I only need a couple for a bit of experimentation.  I'm in Melbourne, if

I have a control box with a 2 wire cable going out to a SPST switch that
switches 120V AC line.  I want to put a socket on in the box and a plug
on the wire with the switch so I can disconnect it when it isn't
needed.  The easiest thing I can think of  would be to use a standard ...

Looking for the pinout details for an obsolete (?) IC - MC14410, DTMF
encoder (Motorola I believe).  Yes, I've tried Google and several datasheet
sites, with no luck.  I only need the pin designations not the whole
datasheet, so if anyone can help by posting the info it'd be much ...

I was just working on an amp today and pulled a transistor out for testing
(with the very brilliant, Atlas tester). I had a thought: Transistors could
be made with a fourth lead. This lead would allow a sophisticated (but
inexpensive) testers (such as the Atlas) to interrogate ...

I understand the term 'Bandwidth' when used to refer to a range of
frequencies, eg Fmin to Fmax.
But I often hear the term used in place of 'frequency' and I wonder if
and when this should be done.

Basically what I want to do is have a small box with
speakers and a looping sound sample of bridge sounds
from Star Trek as a background sound for a room.
Is there any form of solid state recording chip to store

I heard somewhere that the leads of common electronic components (resistors,
capacitors, transistors etc), such as you might buy from Dick Smith
Electronics are tinned with a lead based compound. Is this correct? Any help
with this query would be appreciated.

what the issue with this "new law" which comes about next year about lead
free semis ? If its law next year then whats going to happen to all the old
semis ??
Chris

Which of this indoor amplified antenna is the best?
1) Crest I3500 (More info at
http://www.crest.com.au/product.php?prodcode=I3500)
Operating Bandwidth:  40 - 860MHz

I have a CATV channel convertor, with AV In & out, RF in & out.
It auto tune from 45MHz to 870 MHz and output an RF signal at 67.75
MHz(VL band)
There is a 42 pin IC with markings

I would like to interface my pc with a pic16F877A, first to program
it using a bootloader, and later to send debugging info from the chip.
The problem is, there are several chips to choose from at both mouser and
digikey. The book I'm using only says MAX232, but there are MAX232N,

I am looking for some e square proms.
The eight legged packages are marked as .... 93C56
If anyone has some... I would like four of them.
They are same to look at as a 555 ic timer package.