windoze killa

Without going into deep detail FR4 is the fire retardent level. FR4 is the most common higher quality type. FR2 is used in cheaper consumer type products. The HASL is basically tinned tracks. The other 2 are electro deposited gold or silver coatings. Much more expensive.

If you are trying to produce a 5V supply and you can't use a 7805 because you only have a 5V input then why not just use that 5V supply.

Most of the system would be run using microcontrollers. You would have to write the code to suit. Basically you would send a request to each car and time how long it takes to get a response. From this you can calculate the distance. The ID would be part of the response.

I missed this post before. Not quite sure hore you can make this statement. A small chip of metal film with 0 ohms would have such an insignificant inductance it would be useless. About the only way I could see this happening is if it was a wire wound 0 ohm resistor

You could also use an optocoupler.

6" shouldn't be a problem so long as you aren't trying to do it over 50'. Reverse parking sensors on cars are ultrasonic and they are pretty rough in design. So a PC based decoder system should be easy.

We use 0 ohm SMD resistors all the time. They are mainly used as links. We design the boards so there are different configurations available. The resistors are placed to select different options.

I worked on 10KW HF transmitters for years and it never affected me, me, me, me,........ ooopppsss

If you use the correct type of soldering iron set to the correct temperature, prepare and clean the pad and component, apply liquid flux and don't be on the joint for more than 3 seconds then there is no need for a heatsink clip. These will just suck heat away from the joint and actually cause a bad joint. If you have the temperature of the iron such that it over comes the effect of the heatsink to allow you to do a good joint you will be overheating you component worse than if you do it properly. Proper tools and proper technique is everything when it comes to soldering. Another rule of thumb for soldering tips is to chose a tip width that is about 2/3 the width of the pad you are trying to solder. Remember these simple rules. (probably can be applied to everything in life) Cleanliness is next to godliness. Practice makes perfect. Your best mate is not an expert in everything. You don't go to a Dr to find out how to fix your car so don't ask a plumber how to solder electronics. (nothing against Drs or plumbers) (except for the way they charge)

Sounds like a micro might be the easiest for this job.

I would assume you are going to do all this with some PC or micro. If this is the case then you could track as many cars as you would like. You would just have to give each one an ID number and poll the system to check for each car in turn. All this can be done in fractions of seconds. The other advantage of ultrasonics is it is less suseptible to losing signal if the trancducer get dirty. If you got dirt on an IR diode it would be useless until you removed it.

There are a few deciaml to binary/BCD chips available. Have a look at http://pdf1.alldatasheet.com/datasheet-pdf/view/27380/TI/SN74147N.html

Does this mean you will stop using your computer???? It probably radiates more RF than a bluetooth device. There is so much radiation floating around these days. All the power wires running through your house and out in the street.

There are also some areas in Tasmania over heer in OZ that are using power lines (the big ones outside) for telephone and internet. Got the phone companies running scared.