[RS232 to 20ma current loop converter]

After AT, PC com ports no longer support the current loop option.
The current loop is used for higher speeds and
longer distances than regular RS232. It might be in the original
specification, but not in all the products.  There are lots of devices
that use this today because higher distance,  noise immunity and speed it provides.
It is also used in sensors and control applications.

I see lots of commercial products out there which perform this function.
I just wanted to build one.  I am not sure of the difference between
current loop and RS485 (long wire extended or 2 wire RS232) but one
company offering products had a version for both.

Incidently, because I need this for a printer, I could get by fine with
a half duplex version, 1200 baud - not really speed critical.

[interfacing a webcam to an external ram]

1 mp digital cameras are a dime a dozen these days and take a better still then
many web cams I've seen.  They come ready to go with ram.  I would open one
up and run external wires to the shutter switch and the battery connectors.  Many will plug right into a usb on a laptop.

[Long distance car sensor.]

If you can cover the area with a wireless camera,  and feed the receiver into the
usb port of your computer with an adapter or into a video board, there is software available to monitor the image for movement.  The pc could take a snapshot and alert you with a tone.  I tried this trick on my driveway but the camera I selected had poor nite vision capabilities.  The software I found on the internet was shareware.

[RS232 to 20ma current loop converter]

I am looking for a schematic for an RS232 (from a PC serial port) to a
serial receipt printer that uses 20ma current loop on a DB25 connector.
If I am not mistaken, it should be able to be done with a couple opto-
isolators (transistor). 

[Semi Manufacturer's Icon symbols]

Does anyone have a chart or link with many of the symbols identified that are
found on the semiconductors and ICs?  It can be the first place to start in
locating the datasheet.

[switching pwr supplies level1? level3?]

???
The 12volt 4amp external switching power supply for my lcd monitor burned out.
On the back it states it is a "level 3"

I found another 12volt 4amp switching power supply that states it is a
"level 1" power supply

Does anyone know the difference between these and if it is risky to
run the lcd with a level 1 power supply?

[An excellent electronics manual]

After running across this at the public library in town, I just had
to order my own copy:
"Practical Electronics for Inventors"  by Paul Scherz

It covers just about everything from DC to Microcontrollers and is well illustrated.