A "rheostat" is a variable resistor. There may be other words that mean the same thing, but in general, no matter what the design, they all let you select an electrical-resistance value from nearly zero (sometimes including zero) on up to its maximum rating. The manual volume control of any old radio is a rheostat.

So, start with a cell phone. Add a rheostat between the battery and the rest of the circuitry of the phone. Dial this rheostat to the minimum setting. Everything works normally.

Now you receive a telephone call from somebody who doesn't know how to quit talking. Start turning the rheostat dial. This will reduce the amount of power flowing from the battery to the phone. Strange things will begin to happen to the conversation. You can truthfully claim that you think your phone is having a power problem, and you might have to recharge the battery. Then hang up, and reset the power dial back to minimum resistance.
-- Vernon, Jun 24 2004

A.K.A. potentiometer http://www.geofex.c...ecrets/potscret.htm
For those who want to know more. [Vernon, Oct 04 2004, last modified Oct 21 2004]

Some little ones http://www.farnswor.../potentiometers.htm
One of these is probably suited for cell-phone use. For some unknown reason, the word "potentiometer" typically is applied to small rheostats. [Vernon, Oct 04 2004, last modified Oct 21 2004]

(?) Some big ones http://www.jenkins....rols/plate_rheo.htm
And the word "rheostat" typically is applied to large potentiometers :) [Vernon, Oct 04 2004, last modified Oct 21 2004]

Hmmm... zero resistance? Really? A superconductor setting on a rheostat, awesome. That could be an idea in itself : ) Anyways, I usually just lie. But a bun for the sake of the chronically honest.
-- evilmathgenius, Jun 24 2004


[evilmathgenius], it could possibly be hedged that when a rheostat allows itself to be completely removed from the circuit (the current bypasses its resistance-element), then its resistance is zero. But yes, I do agree that even then, the resistance isn't actually exactly zero, because ordinary wires (which do the bypassing) aren't superconductive.
-- Vernon, Jun 24 2004


Problem is, I'd think that if you left the rheostat (potentiometer or variable resistor, in more electronic terms) turned up for any length of time, the resistance would *actually* drain the battery quite a bit, and then you wouldn't be able to just turn it off again. You also need a way to dissipate the heat given off by the resistance, or you'll burn out your potentiometer right quick (yes, I played with these things in the basement when I was a kid, and burned myself).
-- Etymon, Jun 24 2004


Some of us are electrical engineers but say rheostat because it's a fun word... ahem.
-- evilmathgenius, Jun 24 2004


[Etymon], Yes, some power will be wasted by the rheostat. But ONLY when the phone is on; see that word "between" in the second paragraph of the main text. I am specifying a series circuit here, battery to rheostat to rest-of-phone. So when the phone is off, no current flows through the rheostat.

Now of course I know that the phone is actually slightly ON most of the time, so that it can recognize an incoming call. In this case leaving the rheostat turned up will likely interfere with reception enough that you would receive no calls. Also, depending on how much total resistance you can dial (10K Ohms, maybe, and probably accidently), it is possible that only a trickle of current would be wasting itself inside rheostat. That will hurt the battery life very little.

Next, the total heat produced will depend on the power dissipated by the resistance. It ALSO depends on the voltage of the battery -- which I think is usually pretty low for a cell phone (3 or 6?). Well, since the NORMAL current flow to the phone is probably measured in milliamps (for decent battery life), it follows that if all of it went through a rheostat, the wasted power would be (volts * amps) less than a watt. Maybe a couple of watts at most -- and that will be lessened, the more you turn the dial. SO, I'm pretty sure heat is not a problem here.
-- Vernon, Jun 24 2004


Bun for the idea, fish for the implementation.

Don't waste critical battery power (albeit small) using a power rheostat (variable resistor with two terminals.) Instead, use a high value / low current potentiometer (variable resistor with 3 terminals) to determine the desired voltage and switch mode regulate the voltage supplied to the phone.

On second thought, with typical digital cell phones, you are unlikely to get graceful degradation, more likely all will be fine until the error correction circuitry can't keep up, and one falls off the digital "cliff."

Simple software update to the cell phone could introduce intentional variable noise level controlled using up/down arrow keys. Download different background distracting noises from the internet!

Could become as popular as polyphonic ring tones!
-- csea, Jun 24 2004


Just yell a few times "Hello, hello, can you hear me?" and then hang up.
-- kbecker, Jun 24 2004


i'm with [kbecker], but i usually just hang up.
-- xclamp, Jun 24 2004


Cell phones with rotary dials... hmmm....
-- RayfordSteele, Jun 24 2004


My phone transmission quality doesn't go down as the battery dies. It just beeps three times and shuts off.
-- Freefall, Jun 24 2004


Yeah, cell phones are really picky about voltage, if they get below 3 volts, they are no longer able to turn on. SOme will attempt to turn on, try to find service but not have enough power to search for service and so will shut off, sometimes with an error message like "ERROR! battery power is too low" or "low battery! powering off". I think that the circuits that "drive" the antenna require a lot more power than the rest of the phone, and the phone powers on the main board, the screen and then tries to search for service, but theres not enough power to transmit/recieve signals, and so the phone shuts off. That's my theory on why they just go belly up instead of slowly degrading in performance.
-- Dickcheney6, May 01 2008



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