Reducing noise in an output signal from a sensor

[kanboy]

Hi,

I would like to use PIC16F877 to convert the analog signal from an accelerometer to digital, then i would use the digital signal to control a solenoid to hit a bell. But the output signal from the sensor is too small ( a few mV) hence, it is interfered by noise, so i can't get anything at all. I intend to use an instrumental amplifier and a low pass filter to get rid of the noise. that is just an idea. Any other recommendation? Please feel free to give any idea or recommendation.

regards

 

[instruite]

Re: signal from sensor

Hi,
The signal from the sensor (analog type) is normally never fed directly to the microcntroller.
Usually, there is always some signal conditioning circuit in between sensor and micrcontroller.
The signal conditioning circuit usually consists of
1) Input resistor - pullup in case of open collector or drain type sensor
pulldown in case of source type sensors

2) amplifier - depending on the sensor output voltage the amplifier is used. If the sensor voltage is same as the analog in put voltage range of the microcontroller then there is no need for amplifier
The amplifier can be normal single opamp amplifier also no need for instrumentation amplifier unless it is really neccessary

3) Low pass filter - a simple RC circuit (in our designs we normally use RC time constant of 1ms for all the analog sensors)

 

[noiseless]

signal from sensor

or bandpass filter if you know the signal frequency

 

[mohamedtaha]

Re: signal from sensor

The problem of low mV output sensors is the power frequency noise (50 or 60 Hz). you should use a low pass filter after your amplifier and don't negelct decoupling capacitors on all IC even analog ones. The analog ground should be isolated from the digital ground if possible. the ground wire should have the least impedance possible.you may valuable information on the Analog Devices web site.