Multiplexer Exapansion Board

This section provides a short guide to help you begin using your Rodeostat in conjunction with the multiplexer expansion board. This expansion board enables the Rodeostat to use up to seven independent working electrodes simultaneously. When connected to the Rodeostat additional features provided multiplexer may accessed programmatically via the Python API.

Enabling/Disabling the multiplexer

In order to use the multiplexer it must first be enabled. This can be done using the set_mux_enabled() method. To enable the multiplexer you would run the following command

rsp = pstat.set_mux_enabled(True)

Similarly in order to disable the multiplexer you would run the command shown below

rsp = pstat.set_mux_enabled(False)

The response returned by the set_mux_enabled() will be either True/False indicating whether or not the multiplexer has been successfully enabled/disabled respectively.

Setting the working electrode channels

The multiplexer has seven working electrode channels. You don’t need to use all the working electrode channels and the same time. The subset of working electrode channel which are enabled can be set using the set_enabled_mux_channels() method. For example, the following command will enable working electrode channels 1, 3 and 7.

pstat.set_enabled_mux_channels([1,3,7])

To query the device for the list of currently enabled working electrode channels you can using the get_enabled_mux_channels() method. For example the command

channel_list = pstat.get_enabled_mux_channels()

In order to run a test with the multiplexer expansion board the firmware requires that at least one working electrode channel is enabled.

Running tests

Running tests with the multiplexer expansion board enabled is almost exactly the same as normal using the run_test() method. For example, in order to run the cyclic voltammetry test you could do the following.

data_dict = pstat.run_test('cyclic')

The main difference is that when the multiplexer is enabled the run_test() returns a dictionary containing the measured data for each channel rather than a tuple of times, voltages and currents. The keys of the dictionary returned are the enabled channel numbers and the values are dictionaries with the time, voltage and current measurments for that channel, keyed by ‘t’, ‘v’, and ‘i’ respectively. Thus the time, voltage and current data for channel 1 can be accessed as follows.

chan1_time = data_dict[1]['t']  # channel 1, list of sample times
chan1_volt = data_dict[1]['v']  # channel 1, list of output voltages
chan1_curr = data_dict[1]['i']  # channel 1, list of current samples

The parameters for the test can be set as usual using the set_param() method as described in the Setting voltammetric test parameters subsection, or by specifying the parameters using the params keyword argument to the run_test() method as shown below

my_param = {
    'quietValue' : 0.0,
    'quietTime'  : 1000,
    'amplitude'  : 2.0,
    'offset'     : 0.0,
    'period'     : 1000,
    'numCycles'  : 5,
    'shift'      : 0.0,
    }

data_dict  = pstat.run_test('cyclic', param=my_param)

Note

When using the multiplexer all electrodes (counter, reference and working) are on digitally controlled switches. By default, when not running a test, the electrodes will be disconnected. When using the run_test() method the electrodes will be automatically connected using these switches prior to running the test. Similarly, after the test is complete, the electrodes will be automatically disconnected.

Note

At this time the squareWave test is not compatible with the multiplexer expansion board. Attempting to run this when the multiplexer is enabled will result in an error.

To get a list of the test which are compatibile with the multiplexer the get_mux_test_names() can be used.

test_names = pstat.get_mux_test_names()

This command will return a list such as that shown below

test_names = ['cyclic', 'sinusoid', 'constant', 'linearSweep', 'chronoamp', 'multiStep']

Manual/direct operation when the multiplexer

When using the Rodeostat with the multiplexer expansion board in manual/direct control mode a few special considerations are required. By default all electrodes (counter, reference and working) are disconnected and you must manually specify in software when you want to connect a specific electrode. The methods used for the reference and counter electrodes this are:

set_mux_ctr_elect_connected() which connects/disconnects the counter electrode

set_mux_ref_elect_connected() which connects/disconnects the reference electrode

For example, the following commmands connect the counter and reference electrodes.

pstat.set_mux_ctr_elect_connected(True)   # connect the counter electrode
pstat.set_mux_ref_elect_connected(True)   # connect the reference electrode

Similarly, the counter and referece electrodes can be disconnected as shown below.

pstat.set_mux_ctr_elect_connected(False)   # disconnect the counter electrode
pstat.set_mux_ref_elect_connected(False)   # disconnect the reference electrode

The enabled working electrodes are automatically connected to multiplexer. In addition the working electrodes can be connected to current measurement circuit (transimpedance amplifier) via the make-before-break multiplexer using the set_mux_wrk_elect_connected() method. This command takes as an argument the number of the working electrode you would like to connect to the measurement circuit. For example, to connect working electrode number 3 to the current measurement circuit you would use the folling command.

pstat.set_mux_wrk_elect_connected(3)  # connect working electrode number 3 to TIA

Note

Only one enabled working electrode can be connected to the measurement circuit at a time. For example, if working electrode number 3 is connected the the current measurement and you wish to connect working electrode 5 to this circuit you can do this by running the command pstat.set_mux_wrk_elect_connected(5). This will connect working electrode 5 to the measurement circuit. However, prior to connecting working electrode 5, working electrode 3 will first be disconnected, using the a make-before-break protocol, before connecting electrode 5.

To disconnect all working electrodes from the measurement circuit the you can run the set_mux_wrk_elect_connected() method with an argument of False. For example,

pstat.set_mux_wrk_elect_connected(False)  # disconnect all working electrodes from TIA

Note

When working electrodes are enabled the are connected electronically to the multiplexer (and Rodeostat). At this point the can sink/source current. The set_mux_wrk_elect_connected() just selects which of the enabled working electrodes is connect to current measurent circuit (transimpedance amplifier) using the make-before-break protocol.

To disconnect all electrodes (counter, reference and working) with a single command the disconnect_all_mux_elect() method may be used as shown below.

pstat.disconnect_all_mux_elect()  # disconnect all electrodes