From ab8dbe2701592437602612a2557ce4d862d06a05 Mon Sep 17 00:00:00 2001
From: Jens Ahrensfeld <jens@jayfield.org>
Date: Sun, 31 Mar 2019 06:06:16 +0000
Subject: [PATCH] - added temperature sensor driver

git-svn-id: http://moon:8086/svn/projects/HendiControl@188 fda53097-d464-4ada-af97-ba876c37ca34
---
 Control/brewpi/max31865.py | 89 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100755 Control/brewpi/max31865.py

diff --git a/Control/brewpi/max31865.py b/Control/brewpi/max31865.py
new file mode 100755
index 0000000..b68d011
--- /dev/null
+++ b/Control/brewpi/max31865.py
@@ -0,0 +1,89 @@
+#!/usr/bin/python
+
+import spidev
+import time
+import os
+ 
+# Open SPI bus
+spi = spidev.SpiDev()
+spi.open(0,0)
+spi.max_speed_hz=100000
+spi.mode = 0b01
+
+def read_reg(addr):
+	reg = spi.xfer([addr, 0xFF]);
+
+	return reg[1]
+	
+def write_reg(addr, data):
+	spi.xfer([addr+0x80, data]);
+
+def read_digits():
+	msb = read_reg(0x01)
+	lsb = read_reg(0x02)
+	digits = float(256*msb + lsb)/2
+
+	return digits
+
+def calc_R(Rref, digits):
+	k = digits / 8192 / 4
+	R = k*Rref
+
+	return R
+
+def vanDusenLut (R0, Tmin, Tmax, dT):
+	a = +3.90830e-03;
+	b = -5.77500e-07;
+	c = -4.18301e-12;
+
+	Rv = []
+	Tv = []
+	T = Tmin
+	while T <= Tmax:
+		R = R0*(1 + a*T + b*T**2)
+
+		if T < 0.0:
+			R += R0*c*(T - 100)*T**3;
+		
+		Rv.append(R)
+		Tv.append(T)
+		T += dT
+
+	return Rv, Tv
+
+def vanDusen_temp(Rmeas):
+	RLut, TLut = vanDusenLut(100, -150, +500, 1.0)
+
+	# Find candidate
+	i = 0
+	for R in RLut:
+		if R > Rmeas:
+			break
+		i += 1
+
+	# Linear interpolation
+	R0 = RLut[i-1]
+	R1 = RLut[i]
+	T0 = TLut[i-1]
+	T1 = TLut[i]
+
+	dR = R1 - R0
+	dT = T1 - T0
+
+	k = (Rmeas-R0)/dR
+	T = T0 + dT*k
+
+	return T
+
+# Main
+write_reg(0x00, 0xA3)
+digits = read_digits()
+R = calc_R(430, digits)
+T = vanDusen_temp(R)
+print("R={:.3f} Ohm, T={:.2f} degC".format(R, T))
+
+for i in range (0, 8):
+	print("Reg[0x{}]: 0x{:02X}".format(i, read_reg(i)))
+
+print("End of program")
+