A knock sensor example using a piezo element + MCP3008 + Raspberry Pi

    require 'pi_piper'
    #port of the Adafruit MCP3008 interface code found @ http://learn.adafruit.com/send-raspberry-pi-data-to-cosm/python-script

    def read_adc(adc_pin, clockpin, adc_in, adc_out, cspin)
      cspin.on
      clockpin.off
      cspin.off
      
      command_out = adc_pin
      command_out |= 0x18
      command_out <<= 3

      (0..4).each do
        adc_in.update_value((command_out & 0x80) > 0)
        command_out <<= 1
        clockpin.on
        clockpin.off
      end
      result = 0

      (0..11).each do
        clockpin.on
        clockpin.off
        result <<= 1
        adc_out.read
        if adc_out.on?
          result |= 0x1
        end
      end 

      cspin.on

      result >> 1
    end
      
    clock = PiPiper::Pin.new :pin => 18, :direction => :out
    adc_out = PiPiper::Pin.new :pin => 23
    adc_in = PiPiper::Pin.new :pin => 24, :direction => :out
    cs = PiPiper::Pin.new :pin => 25, :direction => :out

    adc_pin = 0

    loop do
      value = read_adc(adc_pin, clock, adc_in, adc_out, cs)
      puts 'val : ' + value.inspect if value > 5
      sleep 0.01
    end

Output:

<pre>
val : 6
val : 38
val : 22
val : 19
val : 32
val : 28
val : 12
val : 36
val : 26
val : 10
val : 6
val : 183
val : 35
val : 67
val : 38
val : 85
val : 29
</pre>

The above output was created when I tapped my finger close to the piezo element. The harder I tap, the larger the value.

Note: The threshold was set to 5 because the value when idling floated between 0 and 3.

## Resources

* Using a Photocell + MCP3008 + Raspberry Pi + Pi_piper gem http://www.jamesrobertson.me.uk/snippets/2016/feb/19/using-a-photocell-mcp3008-raspberry-pi-pi_piper-gem.html
* A simple knock sensor example http://www.jamesrobertson.me.uk/arduino/2016/mar/06/a-simple-knock-sensor-example.html

piezoelement knocksensor sensor mcp3008