initial version

README.md

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+# BK Precision 1696
+
+This is a Python library for communicating with the [BK Precision 1696][psup]
+power supply via its serial interface. You can control the supply's parameters
+and take voltage/current readings.
+
+For example:
+
+    import psup
+    with psup.Supply() as sup:
+        sup.voltage(1.3)
+        volts, amps = sup.reading()
+        print '%f V, %f A' % (volts, amps)
+
+For more details, see [my blog post][blog] about a setup using this library to
+measure the dynamic power of a smartphone.
+
+[psup]: http://www.bkprecision.com/products/model/1696/programmable-dc-power-supply-1-20vdc-0-999a.html
+[blog]: http://www.cs.washington.edu/homes/asampson/blog/powermeasurement.html

psup.py

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+from __future__ import division
+import serial
+import glob
+import time
+import decimal
+
+def _str2num(num, factor=10):
+    """Takes a number in the supply's format, which always has one
+    decimal place, and returns a decimal number reflecting it.
+    """
+    return decimal.Decimal(num) / factor
+def _num2str(s, length=3, factor=10):
+    """Turns a number, which may be a decimal, integer, or float,
+    and turns it into a supply-formatted string.
+    """
+    dec = decimal.Decimal(s)
+    return ('%0' + str(length) + 'i') % int(dec * factor)
+def _numfields(s, fields, factor=10):
+    """Generates numbers of the given lengths in the string.
+    """
+    pos = 0
+    for field in fields:
+        yield _str2num(s[pos:pos+field], factor)
+        pos += field
+
+class Supply(object):
+    def __init__(self, ident=None):
+        if not ident:
+            # Discover a device.
+            devices = glob.glob('/dev/tty.PL*') # Mac OS X
+            devices += glob.glob('/dev/ttyUSB*') # Linux
+            ident = devices[0]
+        self.ser = serial.Serial(ident, 9600, 8, 'N', 1)
+
+    def command(self, code, param='', address='00'):
+        # Put this communication in an isolated little transaction.
+        self.ser.flushInput()
+        self.ser.flushOutput()
+
+        self.ser.write(code + address + param + "\r")
+        self.ser.flush()
+
+        out = None
+        while True:
+            # Read until CR.
+            resp = ''
+            while True:
+                char = self.ser.read()
+                resp += char
+                if char == '\r':
+                    break
+
+            if resp == 'OK\r':
+                return out
+
+            if out is not None:
+                print 'received more than one line of output without OK!'
+                return resp
+
+            out = resp
+
+    def start(self):
+        self.command('SESS')
+    def close(self):
+        self.command('ENDS')
+    def voltage(self, volts):
+        self.command('VOLT', _num2str(volts))
+    def reading(self):
+        resp = self.command('GETD')
+        volts, amps = _numfields(resp, (4, 4), 1)
+        return volts/100, amps/1000
+    def maxima(self):
+        resp = self.command('GMAX')
+        return tuple(_numfields(resp, (3, 3)))
+    def settings(self):
+        resp = self.command('GETS')
+        return tuple(_numfields(resp, (3, 3)))
+    def enable(self):
+        """Enable output."""
+        self.command('SOUT', '1')
+    def disable(self):
+        """Enable output."""
+        self.command('SOUT', '0')
+
+    # Context manager.
+    def __enter__(self):
+        self.start()
+        return self
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.close()
+
+# Just some tests to show it's working.
+if __name__ == '__main__':
+    with Supply() as sup:
+        time.sleep(0.5)
+        sup.voltage(1.3)
+        sup.enable()
+        time.sleep(0.5)
+        print 'Reading', sup.reading()
+        print 'Maxima', sup.maxima()
+        print 'Settings', sup.settings()
+        sup.disable()
+        print 'Disabled; reading', sup.reading()
+        time.sleep(0.5)