fix crash that happens if no threshold given (#60)

Author: alustig3

pyControl/hardware.py

@@ -233,7 +233,8 @@ def __init__(self, pin, name, sampling_rate, threshold=None, rising_event=None,
     def _run_start(self):
         self.timer.init(freq=self.Analog_channel.sampling_rate)
         self.timer.callback(self._timer_ISR)
-        self.threshold.run_start(self.read_sample())
+        if self.threshold:
+            self.threshold.run_start(self.read_sample())
 
     def _run_stop(self):
         self.timer.deinit()
@@ -477,4 +478,4 @@ def _timer_callback(self):
             timer.set(self.pulse_dur, fw.hardw_typ, self.ID)
             fw.data_output_queue.put((fw.current_time, fw.event_typ, self.event_ID))
         self.state = not self.state
-        self.sync_pin.value(self.state)
+        self.sync_pin.value(self.state)