Voltage Regulator, and Analog Accelerometer

[37637598]

Hello, my first question is about the circuitry involved in one voltage regulator. I have an AMS1117 3V regulator, and I need to know how to hook it up. My supply voltage is 5V, the regulator has 3 pins. VIN, VOUT, and GROUND. This is how I have it connected in the circuit:

Ground - Ground
VIN - 5V+
Vout - accelerometer VS

I've seen many schematics using voltage regulators, that implement capacitors, a diode, and resistors. Do I need to consider any of this to make my regulator work efficiently? As of now, it seems to be dropping the voltage to 3V, but if I increase the input voltage, the output voltage also increases.

Question 2: I have an ADXL335 accelerometer which is powered by the above mentioned regulator, and its analog X, Y, Z outputs are connected to the analog (ADC) input pins of a 16F684 microcontroller. Is this correct, or do I need to add any capacitors / resistors / amplifiers between the analog output of the accelerometer, and the input pins of the microcontroller?

Any help is great help, thanks in advance!

 

[siongboon]

1) The connection should works fine.
A capacitor at the input/output would be good to have but
I don't think it maybe necessary.
The capacitor is to stabilize the voltage.

2) It depend on the interface.
I think your IC should be able to connect to the microcontroller directly.
If there is any issue/problem, you will have to building interface circuit.

 

[pauloynski]

With respect to the AMS1117, it comes in many packages and variations. If you´re using the fixed output voltage type then you don´t need to worry about external resistors. Since you´ve reported the voltage varies with respect to the input voltage it seems you have an adjustable output voltage one. Please refer to the attached datasheet.

 

[svhb]

Watch out for stability with these kind of components (see page 4 of following data sheet) :

The circuit design used in the AMS1117 series requires the use of
an output capacitor as part of the device frequency compensation.
The addition of 22μF solid tantalum on the output will ensure
stability for all operating conditions.
When the adjustment terminal is bypassed with a capacitor to
improve the ripple rejection, the requirement for an output
capacitor increases. The value of 22μF tantalum covers all cases of
bypassing the adjustment terminal. Without bypassing the
adjustment terminal smaller capacitors can be used with equally
good results.
To further improve stability and transient response of these
devices larger values of output capacitor can be used.

I just mention this, because it can save you lots of troubles just adding the capacitor.

Stefaan

 

[37637598]

Great, thanks for the help! That answers all of my questions!

 

[37637598]

New Problem

Okay, so the voltage regulator works perfectly. I now have a new problem.

My circuit uses an ADXL335 analog accelerometer, analog meaning "non digital" (just to clearify because analog also happens to be the maker of the chip). The accelerometer sends a signal to a micro controller, which converts the analog voltage to a digital value, and then determines whether to output to a servo or not. My problem is that the accelerometer calculates an output based on it's supply voltage, but the supply voltage changes when the servo is moving/drawing current. The result: When the accelerometer detects a 20 degree tilt, the servo starts moving and freaking out because as soon as it takes current away, it's command changes due to the voltage drop.

The accelerometer is powered by the voltage regulator, but even the regulators' output changes when the servo is 'on' or moving. The servo is powered by 5V before the regulator. Any suggestions or fixes? I need to make this circuit with as little componants as possible.

Thanks!

 

[pauloynski]

Make sure the 5V supply is not going bellow 4.2V at motor startup. If so, increase the filtering capacitor in parallel with it or use a LDO regulator..