Counter design help

I need to design a circuit that counts the number of times an event occurs in a certain time frame.

Basically, my project will involve accelerometers that are measuring human movement. The output from the accelerometers will be voltage (analog signal). I would like to count the number of times the output from the accelerometers is at or above a certain threshold voltage. For instance, the counter needs to count the number of times the accelerometer is outputting a voltage higher than 1.5V in a time frame of a minute. My timing parameters are to have 30 events (>1.5V) per minute (defined as "success"). When the event is recognized as successful, I want to activate an LED to signify the event and some alarm (like a DC motor for a vibrational alarm?)

I'm confused as to how to make this counter. What do I use? And what is the output signal of the counter, so I can activate the LED and alarm?

apl247 said:

I need to design a circuit that counts the number of times an event occurs in a certain time frame.

Basically, my project will involve accelerometers that are measuring human movement. The output from the accelerometers will be voltage (analog signal). I would like to count the number of times the output from the accelerometers is at or above a certain threshold voltage. For instance, the counter needs to count the number of times the accelerometer is outputting a voltage higher than 1.5V in a time frame of a minute. My timing parameters are to have 30 events (>1.5V) per minute (defined as "success"). When the event is recognized as successful, I want to activate an LED to signify the event and some alarm (like a DC motor for a vibrational alarm?)

I'm confused as to how to make this counter. What do I use? And what is the output signal of the counter, so I can activate the LED and alarm?

Click to expand...

You want to compare an input voltage to a reference voltage: 1.5V. So I'd say you need a comparator. I assume that you want the thing to only count changes at some meaningful speed--i.e. if the thing is right on the edge, you might not want it counting 2000 inputs in the space of a second as the analog voltage input wavers between, say, 1.501V and 1.499V. You might use a Schmitt Trigger to feed the comparator, to ensure that the input must cross 1.5V to trigger a count, but must fall back below some lower voltage (say, 1V) before the input can be triggered again. This is called "hysteresis".

You could most easily use a microcontroller such as a PIC or AVR to count the inputs and control any output devices. More people on this site use PICs than AVRs--there are a lot of PIC gurus here. (I'm not one of them, BTW.)

But before worrying too much about the microcontroller side of it, let's work out the input. Do you have a model name/number for the accelerometer, or a datasheet you could link to?


Torben

Thanks, the schmitt trigger comparator seems appropriate since I do not want the counter to count an wavering voltage at the threshold.

I am not allowed to use microcontrollers in the project. I have the feed the signal from the sensor to digital circuitry for timing and gate functions. Do you have suggestions as to how my timing parameters can be done through digital blocks? And then how to use the signal from the digital blocks to activate the additional modules of a dc motor and LED (which I am thinking would involve the signal triggering an activation of a DC supply voltage to turn both the LED and motor on, and then I would need to deactivate it after some time).

Thanks!

The accelerometer that I am looking at is the analog devices, ADXL 330

the link is https://www.analog.com/en/mems-and-...ters/ADXL330/products/product.html#quicklinks and the datasheet is found here: https://www.electro-tech-online.com/custompdfs/2008/09/ADXL330.pdf