measure the tilt with ADXL330/202 + atmega8

Let's say im absolute amateur in microcontrollers.
I'm working on a project to measure the inclination with accelerometer..
I tend to use analog output ..I picked the Adxl330 with -/+3g (3axis)..Suplly voltage would be 3V in my case..
Is enough to utilize only one Axis to get a tilt?
Im strugglin with op amp follower..
The output impedance of adxl is 32kOhm..The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ..
What should i consider now?
Resolution?
Noise? There are few hints how to cancel analog noice in the datasheets for atmega8.
I need some direction where i should look ..any ideas?or recommend me site/book where i can find more about the ADC problems..Which ive visited yet,haven't told me so much..

Since your just starting out with microntrollers why not something simple like flash an LED? Also for AVR stuff have you tried **broken link removed** ?

blueroomelectronics said:

Since your just starting out with microntrollers why not something simple like flash an LED? Also for AVR stuff have you tried **broken link removed** ?

Click to expand...

Yes,i'm there either,but haven't find the thing which could get me closer to my problem I started with the examples like flash the LED,some playing with registers,interrupts,but all i did was on evaluation board.
Is the real reason to use buffer (op amp) only for decrease output impedance?

Allright can anybody help me to solve this misterY..
I've found the op which should be good to go with accelerometer
How do i know what's the main purpose of this OP?
I was thinking because of get lower the output impedance.

Yes, and to give x15 gain.

C2 should got value 0.33uF...
That was fast response.How did you figure out its 15..Need the formula..
What ive seen so far is Vs=Vout with Voltage follower and that's aLL.No resistors in voltage follower or capacitors

sm0ker said:

C2 should got value 0.33uF...
That was fast response.How did you figure out its 15..Need the formula..
What ive seen so far is Vs=Vout with Voltage follower and that's aLL.No resistors in voltage follower or capacitors

Click to expand...

Its not x15.

At a frequency of about 1.5Hz, the 100uF capacitor starts looking like 1k Ohms. This is lower end of the bandwidth (At DC gain = 1, capacitor open)
When the input frequency >> greater than lower end, the capacitor looks like a short circuit compared ot the 1k and so the gain = 1 + (150k/1k) = 151 (not 15 !)

The gain will remain this until the opamp begins to run out of loop gain at some upper frequency (opamp dependent) then the gain will follow 20 dB/dec decrease.

Also BTW, the input 1uF to ground makes no sense to me. Its not part of any dynamics other than capacitively loading the previous stage.


Did you follow that? Gain for non inverting config = 1 + (Zf / Z1) where Zf = feedback impedance (just 150k this case) and Z1 is the impedance of the series combo 100uF and 1k.

And yes buffering with a gain stage (x1 or otherwise) also has the benfit of a lower driving impedance.

Optikon said:

Its not x15.

At a frequency of about 1.5Hz, the 100uF capacitor starts looking like 1k Ohms. This is lower end of the bandwidth (At DC gain = 1, capacitor open)
When the input frequency >> greater than lower end, the capacitor looks like a short circuit compared ot the 1k and so the gain = 1 + (150k/1k) = 151 (not 15 !)

Click to expand...

Sorry, I read the feedback resistor as 15K

Here i am again...

I drew the scheme.My calculation and datasheet proofed the output of X_FILT and Y_FIL will be the 300mV/g...My purpose is to measure the tilt..If i tilt the sensor 90 degrees,the change is 300mv...Voltage VCC is 5V...

The 0g offset 5V/2 = 2.5V +/-300mV... 300mV when i tilt the sensor 90degree.It's maximum in my project.
What does the supply voltage in OP amp?Only comparation right?
What if i need the Amplification about 5 -> so 2.5V +/-1,5V?
Would be that enough?Are there some calculation of ADC at atmega8?
I want to get a til 1 degree at least..
Which Op amp do you suggest?What else should i consider next?

got a lot of questions i know

sm0ker said:

Here i am again...

I drew the scheme.My calculation and datasheet proofed the output of X_FILT and Y_FIL will be the 300mV/g...My purpose is to measure the tilt..If i tilt the sensor 90 degrees,the change is 300mv...Voltage VCC is 5V...

The 0g offset 5V/2 = 2.5V +/-300mV... 300mV when i tilt the sensor 90degree.It's maximum in my project.
What does the supply voltage in OP amp?Only comparation right?
What if i need the Amplification about 5 -> so 2.5V +/-1,5V?
Would be that enough?Are there some calculation of ADC at atmega8?
I want to get a til 1 degree at least..
Which Op amp do you suggest?What else should i consider next?

got a lot of questions i know

Click to expand...

I can't find a datasheet for ICL762JD.
Why don't you use the duty cycle modulated outputs of the ADXL202?

I said PWM no..I want to explore area of the OP's and the ADC on atmega.Got some tutorials how to do it though..

The only reason to use ICL762JD was to "get a picture" ,it's voltage follower...I havent looked for the right one which fit to my use..
I'm calculating now, the resolution declines after 45 degree..I really have to put the buffer amplifier with the gain about 5...

nobody here is interested in the accelerometeRs?I got through threads concern accelerometers,there were created years ago..

Why cant you use kionix accelerometer

I using kionix KXP84-1050 +-2g digital accelerometer with PIC interface to get acceleration.

I think you can use this n it is so simple to understand n easy to operate. It gives analog output and also digital output with spi/i2c interface.

bye, all the best.