BME280 Linux library for Ruby

bme280.rb

=begin

Copyright 2018 Javier Valencia

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, 
   this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, 
   this list of conditions and the following disclaimer in the documentation 
   and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors 
   may be used to endorse or promote products derived from this software 
   without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND 
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
THE POSSIBILITY OF SUCH DAMAGE.

=end

require_relative "i2cdev"

class BME280 < I2CDev
	
	R_DIG_T1 = 0x88
	R_DIG_P1 = 0x8E
	R_DIG_H1 = 0xA1
	R_DIG_H2 = 0xE1
	R_PRESS_MSB = 0xF7
	R_CTRL_HUM = 0xF2
	R_CTRL_MEAS = 0xF4
	
	def self.base_address
		0x76
	end
	
	def initialize(*params)
		super(*params)
		@sensors = {}
		setup
	end
	
	def update
		adc = adc_read
		t_fine = calc_t_fine(adc[:t])
		
		@sensors[:t] = compensate_t(t_fine)
		@sensors[:p] = compensate_p(adc[:p], t_fine)
		@sensors[:h] = compensate_h(adc[:h], t_fine)
	end
	
	def temperature
		update if @sensors.empty?
		@sensors[:t].round(2)
	end
	
	def pressure
		update if @sensors.empty?
		@sensors[:p].round(2)
	end

	def humidity
		update if @sensors.empty?
		@sensors[:h].round(2)
	end

	private
	
	def setup
		i2c_write(R_CTRL_HUM, 0x05)
		i2c_write(R_CTRL_MEAS, 0xb7)
	end
	
	def calib
		return @cdata if defined?(@cdata)
		
		t_data = i2c_read(R_DIG_T1, 6)
		p_data = i2c_read(R_DIG_P1, 18)
		h_data = ""
		h_data << i2c_read(R_DIG_H1, 1)
		h_data << i2c_read(R_DIG_H2, 7)
		h_data = patch_h_data(h_data)
		
		@cdata = {t: t_data.unpack("S<s<2"), p: p_data.unpack("S<s<8"), h: h_data.unpack("Cs<Cs<2c")}
	end
	
	def patch_h_data(h_data)
		bytes = h_data.bytes
		e5 = bytes[5]
		h4 = (bytes[4] << 4) + (e5 & 0x0f)
		bytes[4] = h4 & 0xff
		bytes[5] = h4 >> 8
		h5 = (e5 >> 4) + (bytes[6] << 4)
		bytes.insert(6, h5 & 0xff)
		bytes[7] = h5 >> 8
		bytes.pack("C*")
	end
	
	def adc_read
		data = i2c_read(R_PRESS_MSB, 8)
		data = patch_adc_data(data)
		p, t, h = data.unpack("L>L>S>")
		
		{p: p >> 12, t: t >> 12, h: h}
	end
	
	def patch_adc_data(adc_data)
		bytes = adc_data.bytes
		bytes.insert(3, 0)
		bytes.insert(7, 0)
		bytes.pack("C*")
	end
	
	def calc_t_fine(adc_t)
		var1 = (adc_t / 16384.0 - calib[:t][0] / 1024.0) * calib[:t][1]
		var2 = ((adc_t / 131072.0 - calib[:t][0] / 8192) ** 2) * calib[:t][2]
		var1 + var2
	end
	
	def compensate_t(t_fine)
		t_fine / 5120.0
	end
	
	def compensate_p(adc_p, t_fine)
		var1 = t_fine / 2.0 - 64000.0
		var2 = (var1 ** 2) * calib[:p][5] / 32768.0
		var2 = var2 + var1 * calib[:p][4] * 2.0
		var2 = var2 / 4.0 + calib[:p][3] * 65536.0
		var1 = (calib[:p][2] * (var1 ** 2) / 524288.0 + calib[:p][1] * var1) / 524288.0
		var1 = (1.0 + var1 / 32768.0) * calib[:p][0]
		
		return 0 if var1 == 0
		
		p = 1048576.0 - adc_p
		p = (p - var2 / 4096.0) * 6250.0 / var1
		var1 = calib[:p][8] * (p ** 2) / 2147483648.0
		var2 = p * calib[:p][7] / 32768.0
		(p + (var1 + var2 + calib[:p][6]) / 16.0) / 100.0
	end
	
	def compensate_h(adc_h, t_fine)
		var = t_fine - 76800.0
		
		return 0 if var.zero?
		
		var = (adc_h - (calib[:h][3] * 64.0 + calib[:h][4] / 16384.0 * var)) * 
			(calib[:h][1] / 65536.0 * (1.0 + calib[:h][5] / 67108864.0 * var * 
			(1.0 + calib[:h][2] / 67108864.0 * var)))
		var = var * (1.0 - calib[:h][0] * var / 524288.0)
		
		if var > 100.0
			var = 100.0
		elsif var < 0.0
			var = 0.0
		end
		
		var
	end
end