From 82b86ca6a3d129cf04a6e2714e6891722970e62d Mon Sep 17 00:00:00 2001
From: Phil Howard <phil@gadgetoid.com>
Date: Fri, 7 Jun 2019 10:49:37 +0100
Subject: [PATCH] Clarified pin use, fixed missing setup

---
 library/envirophatplus/gas.py | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/library/envirophatplus/gas.py b/library/envirophatplus/gas.py
index 9b213ed..4f61940 100644
--- a/library/envirophatplus/gas.py
+++ b/library/envirophatplus/gas.py
@@ -1,9 +1,10 @@
 """Read the MICS6812 via an ads1015 ADC"""
 
+import atexit
 import ads1015
 import RPi.GPIO as GPIO
 
-MICS6812_EN_PIN = 24
+MICS6812_HEATER_PIN = 24
 
 
 ads1015.I2C_ADDRESS_DEFAULT = ads1015.I2C_ADDRESS_ALTERNATE
@@ -40,11 +41,18 @@ def setup():
 
     GPIO.setwarnings(False)
     GPIO.setmode(GPIO.BCM)
-    GPIO.setup(MICS6812_EN_PIN, GPIO.OUT)
-    GPIO.output(MICS6812_EN_PIN, 1)
+    GPIO.setup(MICS6812_HEATER_PIN, GPIO.OUT)
+    GPIO.output(MICS6812_HEATER_PIN, 1)
+    atexit.register(cleanup)
+
+
+def cleanup():
+    GPIO.output(MICS6812_HEATER_PIN, 0)
 
 
 def read_all():
+    """Return gas resistence for oxidising, reducing and NH3"""
+    setup()
     ox = adc.get_voltage('in0/gnd')
     red = adc.get_voltage('in1/gnd')
     nh3 = adc.get_voltage('in2/gnd')
-- 
2.30.2