How to decrease voltage?

Well I want to decrease voltage without having to connect anything to gnd. I want to use an arduino output of maybe 5v and than decrease it to 2.8 v of 40mA

could u make a schematic of zener diodes used to decrease voltage?

so if I want to decrease the voltage of a circuit what do I have to do?(using zener diodes)

U told me to use zener diodes… and I want to reduce voltage from 5v to 2.8 volt and current from 50mA to 40mA (I can do that by a resistor, I already know that). I don’t want to use a voltage regulator that requires u to connect it to gnd.

If I connect a voltage counter on the end of the sensor will I see a value smaller than the source voltage?

Voltage divider with resistors comes out cheaper and works just fine.

http://en.wikipedia.org/wiki/Voltage_divider

Maybe that can get you on track... Let me know if you want more on it..

I know man, but I am not able to connect it to gnd source.

I want to a create an on board circuit which has a sensor and will be connected with an arduino I want to decrease the incoming voltage from arduino, I also want to use on board voltage regulators and I want it to be light, small and efficient. Connecting it to GND would either mean that I will connect it to an arduino input and I am not quite sure if this won't bake my processor or overflow (even a little) my processor. On the other hand connecting it directly to the battery would create problems because the battery is far away from the project extra cables or boards would make the project heavier.

ok screw me… I just now saw the GND pin on the board

If you don't want to connect anything to ground, then insert a component in series that results in the desired voltage drop. Standard diodes have ~.7v voltage drop across them. Colored LEDs have various other voltage drops across them. Three small signal diodes in series with a 5v supply should provide a ~2.1v drop, resulting in ~2.9v available for use.

ok screw me... I just now saw the GND pin on the board

nice ;)

without a ground you wont have electrical flow... :D

without a ground you wont have electrical flow

My car has rubber tires so nothing in it is grounded. Why do the electrical devices in the car still work?

Don

By magic ! it's all done with smoke and mirrors.

A cars electrical system is a self contained system. Battery output to device, out of device and back to battery.

Do not confuse the term "ground" with a stake driven into planet earth. Thos devices are the preserve of vampires.

My car has rubber tires so nothing in it is grounded. Why do the electrical devices in the car still work?

Just as a side point, car tires are very conductive at higher voltages due to the carbon content. Learned that trying to use a piece of innertube as insulation on an electric fence. That is why when a large rubber tired crane hits a high voltage power line, the tires quickly catch on fire.

"Dad, somebody is licking our tires!" - John Waters "Dirty Shame"

Ground: All electrical devices must be part of a circuit. That is, electrons must flow from the power source through the device to a ground. In cars, the metal chassis is the ground (that's why the battery's negative lead is bolted to the engine or frame) and the power source is the positive lead on the battery. Without a ground there is only a POTENTIAL circuit. No electrons will flow - and therefore nothing will work - unless the circuit ends in a ground. Note: Some cars and trucks utilized "positive ground" electrical systems, where the positive lead from the battery connects to the frame and the negative lead goes to the electrical wiring harness. This in no way makes it more difficult to wire or troubleshoot; all that's required is to remember that the system is the reverse of normal systems.

http://www.secondchancegarage.com/public/98.cfm

Just as a side point, car tires are very conductive at higher voltages due to the carbon content.

Sorry, the car scenario was the first stupid example that I could come up with to emphasize how wrong it is to think that a 'ground' is required for current flow. Richard came up with much better examples.

Don

to emphasize how wrong it is to think that a ‘ground’ is required for current flow.

A complete path is ALWAYS required for current flow. In most circuits a common return node is called “ground” or “earth”. But that is just semantics. It doesn’t change the absolute requirement for the complete path.

Your response sums it all up. It is the complete path that is required and the ground that is not required. So we agree. The bottom line, as far as the Arduino is concerned, is that all of the power, input, and output signals are referenced to the GND pin which may or may not be ‘grounded’. How much simpler it would have been if they had labeled it COM.

Don

How much simpler it would have been if they had labeled it COM.

Then you would have had people thinking it was a COM port for serial communications.

perhaps call it a 'sink', or a 'dump'. or perhaps just 0V?

or perhaps just 0V?

Yes that would do it. The point to remember is that a voltage can only be measured between two points. The phrase “this wire has 5 volts on it” is totally meaningless unless you say with reference to what. The stake driven into the planet is a good point of reference BUT it is not the only point of reference.

Anyway I think the OP as gone away now.