A lot of compass apps including Accurate Compass work by using data from the magnetometer sensor in your Android device. Not all devices have this sensor, so the first thing to check is whether your device has — if not you may be out of luck!
The website gsmarena has useful info for many different makes of phone. The compass sensors are very sensitive to interference. Apps for Android. But before you can use a compass app effectively, you have to calibrate your phone's magnetic sensor. Most apps will remind you to do it from the get go, but some won't bother you at all. Either way, they all benefit from the same calibration technique.
To calibrate your Android phone's magnetometer after launching your compass app of choice, hold it up and move it around in a figure 8 fashion.
Several spins should do the trick. While calibrating, make sure you're far from computers, electric fans, Wi-Fi routers, or other electronics as these may interfere with the magnetic sensor and its readings. Metal isn't welcome either, so remove any rings or jewelry that are close to your phone. So now digital compass should be pointing fairly accurately towards the north pole. The basic analog low-dropout voltage regulator [left] controls voltage through a feedback loop.
In the basic digital design [right], an independent clock triggers a comparator [triangle] that compares the reference voltage to V DD.
The result tells control logic how many power PFETs to activate. On a single sliver of silicon it integrates multiple CPU cores, a graphics processing unit, a digital signal processor, a neural processing unit, an image signal processor, as well as a modem and other specialized blocks of logic. Naturally, boosting the clock frequency that drives these logic blocks increases the rate at which they get their work done.
But to operate at a higher frequency, they also need a higher voltage. Without that, transistors can't switch on or off before the next tick of the processor clock. Of course, a higher frequency and voltage comes at the cost of power consumption. So these cores and logic units dynamically change their clock frequencies and supply voltages—often ranging from 0.
These voltages are delivered to areas of the SoC chip along wide interconnects called rails. But the number of connections between the power-management chip and the SoC is limited. But they don't have to all get the same voltage, thanks to the low-dropout voltage regulators. LDOs along with dedicated clock generators allow each core on a shared rail to operate at a unique supply voltage and clock frequency.
The core requiring the highest supply voltage determines the shared V IN value. The power-management chip sets V IN to this value and this core bypasses the LDO altogether through transistors called head switches.
To keep power consumption to a minimum, other cores can operate at a lower supply voltage. Software determines what this voltage should be, and analog LDOs do a pretty good job of supplying it. They are compact, low cost to build, and relatively simple to integrate on a chip, as they do not require large inductors or capacitors. But these LDOs can operate only in a particular window of voltage.
For example, if the supply voltage that would be most efficient for the core is 0. Similarly, if V IN has already been set below a certain voltage limit, the LDO's analog components won't work properly and the circuit can't be engaged to reduce the core supply voltage further.
The main obstacle that has limited use of digital LDOs so far is the slow transient response. However, if the desired voltage falls inside the LDO's window, software enables the circuit and activates a reference voltage equal to the target supply voltage. In the basic analog LDO design, it's by means of an operational amplifier, feedback, and a specialized power p -channel field effect transistor PFET.
The latter is a transistor that reduces its current with increasing voltage to its gate. The op amp continuously compares the circuit's output voltage—the core's supply voltage, or V DD —to the target reference voltage. If the LDO's output voltage falls below the reference voltage—as it would when newly active logic suddenly demands more current—the op amp reduces the power PFET's gate voltage, increasing current and lifting V DD toward the reference voltage value.
Conversely, if the output voltage rises above the reference voltage—as it would when a core's logic is less active—then the op amp increases the transistor's gate voltage to reduce current and lower V DD. The LDO also has its own clock circuit, separate from those used by the processor core. With each tick of the clock, the comparator measures whether the output voltage is below or above the target voltage provided by the reference source.
The comparator output guides the control logic in determining how many of the power PFETs to activate. Their combined current props up the core's supply voltage, and that value feeds back to the comparator to keep it on target. If it overshoots, the comparator signals to the control logic to switch some of the PFETs off. The key advantage of an analog design is that it can respond rapidly to transient droops and overshoots in the supply voltage, which is especially important when those events involve steep changes.
These transients occur because a core's demand for current can go up or down greatly in a matter of nanoseconds. In addition to the fast response, analog LDOs are very good at suppressing variations in V IN that might come in from the other cores on the rails.
And, finally, when current demands are not changing much, it controls the output tightly without constantly overshooting and undershooting the target in a way that introduces ripples in V DD. When a core's current requirement changes suddenly it can cause the LDO's output voltage to overshoot or droop [top]. Basic digital LDO designs do not handle this well [bottom left]. However, a scheme called adaptive sampling with reduced dynamic stability [bottom right] can reduce the extent of the voltage excursion.
It does this by ramping up the LDO's sample frequency when the droop gets too large, allowing the circuit to respond faster. Source: S. Ben Davis January 26, Does a phone compass work without service? Is phone compass magnetic or true? Can you use iPhone compass without signal? What is the best free compass app? Which phone has best compass?
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