add lakeshore demo for hands-on workshop

- a simple LakeShore model 336 driver

a tutorial follows

Change-Id: I291a615efa5bd58a0dd908949210086d2f82c2ca

cfg/ls336_cfg.py

@@ -0,0 +1,18 @@
+Node('example_cryo.psi.ch',  # a globally unique identification
+     'this is an example cryostat for the Frappy tutorial',  # describes the node
+      interface='tcp://10767')  # you might choose any port number > 1024
+Mod('io',  # the name of the module
+    'frappy_demo.lakeshore.LakeshoreIO',  # the class used for communication
+    'communication to main controller',  # a description
+    uri='tcp://129.129.138.78:7777',  # the serial connection
+    )
+Mod('T',
+    'frappy_demo.lakeshore.TemperatureLoop',
+    'Sample Temperature',
+    io='io',
+    channel='A',  # the channel on the LakeShore for this module
+    loop=1,  # the loop to be used
+    value=Param(max=470),  # set the maximum expected T
+    target=Param(max=420),  # set the maximum allowed target T
+    heater_range=3,  # 5 for model 350
+    )

frappy_demo/lakeshore.py

@@ -0,0 +1,108 @@
+#!/usr/bin/env python
+#  -*- coding: utf-8 -*-
+# *****************************************************************************
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+# Module authors:
+#   Markus Zolliker <markus.zolliker@psi.ch>
+# *****************************************************************************
+"""LakeShore demo
+
+demo example for tutorial
+"""
+
+from frappy.core import Readable, Parameter, FloatRange, HasIO, StringIO, Property, StringType, \
+    IDLE, BUSY, WARN, ERROR, Drivable, IntRange
+
+
+class LakeshoreIO(StringIO):
+    wait_before = 0.05  # Lakeshore requires a wait time of 50 ms between commands
+    # Lakeshore commands (see manual)
+    # '*IDN?' is sent on connect, and the reply is checked to match the regexp 'LSCI,.*'
+    identification = [('*IDN?', 'LSCI,.*')]
+
+
+class TemperatureSensor(HasIO, Readable):
+    """a temperature sensor (generic for different models)"""
+    # internal property to configure the channel
+    channel = Property('the Lakeshore channel', datatype=StringType())
+    # 0, 1500 is the allowed range by the LakeShore controller
+    # this range should be restricted in the configuration (see below)
+    value = Parameter(datatype=FloatRange(0, 1500, unit='K'))
+
+    def read_value(self):
+        # the communicate method sends a command and returns the reply
+        reply = self.communicate(f'KRDG?{self.channel}')
+        return float(reply)
+
+    def read_status(self):
+        code = int(self.communicate(f'RDGST?{self.channel}'))
+        if code >= 128:
+            text = 'units overrange'
+        elif code >= 64:
+            text = 'units zero'
+        elif code >= 32:
+            text = 'temperature overrange'
+        elif code >= 16:
+            text = 'temperature underrange'
+        elif code % 2:
+            # ignore 'old reading', as this may happen in normal operation
+            text = 'invalid reading'
+        else:
+            return IDLE, ''
+        return ERROR, text
+
+
+class TemperatureLoop(TemperatureSensor, Drivable):
+    # lakeshore loop number to be used for this module
+    loop = Property('lakeshore loop', IntRange(1, 2), default=1)
+    target = Parameter(datatype=FloatRange(min=0, max=1500, unit='K'))
+    heater_range = Property('heater power range', IntRange(0, 5))  # max. 3 on LakeShore 336
+    tolerance = Parameter('convergence criterion', FloatRange(0), default=0.1, readonly = False)
+    _driving = False
+
+    def write_target(self, target):
+        # reactivate heater in case it was switched off
+        # the command has to be changed in case of model 340 to f'RANGE {self.heater_range};RANGE?'
+        self.communicate(f'RANGE {self.loop},{self.heater_range};RANGE?{self.loop}')
+        reply = self.communicate(f'SETP {self.loop},{target};SETP? {self.loop}')
+        self._driving = True
+        self.status = BUSY, 'target changed'
+        return float(reply)
+
+    def read_target(self):
+        return float(self.communicate(f'SETP?{self.loop}'))
+
+    def read_status(self):
+        code = int(self.communicate(f'RDGST?{self.channel}'))
+        if code >= 128:
+            text = 'units overrange'
+        elif code >= 64:
+            text = 'units zero'
+        elif code >= 32:
+            text = 'temperature overrange'
+        elif code >= 16:
+            text = 'temperature underrange'
+        elif code % 2:
+            # ignore 'old reading', as this may happen in normal operation
+            text = 'invalid reading'
+        elif abs(self.target - self.value) > self.tolerance:
+            if self._driving:
+                return BUSY, 'approaching setpoint'
+            return WARN, 'temperature out of tolerance'
+        else:
+            self._driving = False
+            return IDLE, ''
+        return ERROR, text