External Device Control (digital devices)
a separate page discusses control of analog devices
| Overview | Device groups |
| Output signal coding | Keyboard switching modes |
| Start and finish switching | Periodic switching, several channels |
| Sequential file switching | back to the Topics page |
The 'EXTERNAL DEVICE CONTROL' button in the Display Setup window opens a window for setting up computer-controlled switching of up to eight external devices through one of the Lab-NB (or PCI-1200 or DAQCard-1200) board's digital ports (the software uses Port 2). If you are using an ADC-1, the maximum number of switched devices is six, not eight. Other operations and considerations are the same as for the Lab-NB/PCI-1200/DAQCard-1200.
NOTE: external device control is not available for the Oscilloscope or Multichannel Oscilloscope modes.
CAUTION: external devices, unless they run at < 5 volts with extremely small current drains (e.g., LED's), cannot be driven directly by the Lab-NB/PCI-1200/DAQCard-1200 or the ADC-1/DataTaker. Instead, switch devices through relays, preferably via opto-isolators. The computer's device control lines require devices to be connected to both power and ground. The voltage goes high when a device is switched 'on'.
Warning: If you connect ANY external device to a computer, the responsibility for safe operation is yours, and yours alone. There are NO guarantees or warranties associated with Warthog Systems, and I and the University of California will accept no liability of any kind for the use of this software.
LabHelper works quite well with the Sable Systems Respirometry Multiplexer
(an 8-channel computer-controlled valve bank), but there are a few special considerations.
The timing and order
of LabHelper's switching modes alternate between sample and reference
readings on single or multiple channels. This is particularly useful
for making measurements of metabolism or evaporative water loss during flow-through
respirometry. Five switching modes are selected from the pop-up menu.
In all modes, no more than one of the eight possible devices is switched
on at a given time unless you select the '2 Device
Groups' option. In the latter case, devices 1 through 4 are the
first group and devices 5 through 8 are the second group, and TWO sample
devices are switched on simultaneously (one from each group). There
is one reference device in the normal mode (selected from either group).
If you have selected two device groups, you must select one reference device
from EACH group. To use this option properly, you must have appropriate
plumbing AND make sure that at least one sample device is selected from
BOTH Group 1 (devices 1-4) and Group 2 (devices 5-8).
In this example, the computer is controlling a cluster
of 8 solenoid valves. Four of these valves (2, 4, 6, and 8) are connected
to different animal chambers. The '2 Device Groups' option
is used to split the 4 sample streams into two groups, each of which is
sampled -- ONE AT A TIME -- by one channel
of a 2-channel gas analyzer. Note that for each 'bank' of valves,
another input besides the two connected to animal chambers must contain
a stream of reference air (for example, devices 1 and 5). Also, the
best arrangement for most analyzers is to 'sip' a small fraction of the
excurrent air stream from each chamber. The 'sippers' and gas scrubbers
are not shown here for clarity.
In essence, the computer selects which single device in a group is connected to a sensor at a given time -- either the reference device is connected or one of several possible sample devices.
When using an internal A-D board, LabHelper has
two ways of coding the digital signals to the external device. The
two modes (selectable with the switch code buttons in the upper right
of the window) are:
one line per device (the Warthog default). Each of the 8 output lines in the I/O port is connected to a single device. When the line goes high, the device it is connected to is switched on.
three-bit word. The external device must decode a signal sent on three digital I/O lines (each line represents one bit of the three-bit signal, yielding 8 possible values). NOTE: this coding mode does not allow the '2 Device Groups' option. The Sable Systems Respirometry Multiplexer (an 8-channel valve bank) uses this control scheme (see the special considerations page).
The general switching pattern is shown in a simple graphic
display at the right of the window. Thick bars symbolize a channel
being sampled; thin bars represent reference periods; thin lines indicate
times when a channel is switched off (i.e., set to zero) while another channel
in the same device group is being read. Here is an example of a switching
pattern with the computer set for 'Two Device Groups' mode:
Here, one device (#2) is in use in Group 1, and two devices (#6 and #7) are in use in Group 2. Device 2 is linked to channel 1, device 6 is linked to channel 3, and device 7 is linked to channel 5. Note that #2 (channel 1) samples all the time, but #6 and #7 (channels 3 and 5, respectively) sample alternately. When not being sampled, these channels are set to zero to avoid confusion. The other two channels (2 and 4) are not switched, and hence sample all the time. Devices 4 and 8 are used for reference.
OFF (no
device switching).
MANUAL (KEYBOARD) DEVICE SWITCHING.
The computer turns on a reference device at the
start of a data collection run. The reference device is switched off
and a sampling device is switched on when the '+' (plus-sign) key is struck.
The reverse occurs when the '-' (minus-sign or dash) key is struck.
[Two reference or sampling devices are switched on simultaneously if the
2 Device Group option has been selected.]
If this mode is selected, the user must designate (1) a reference device from the panel in the middle left of the screen, and (2) a sampling device from the panel located at the bottom of the screen. Sampling devices are assigned to particular data channel(s) by entering the appropriate device number for the correct channel in the blue edit fields at the bottom left of the screen (select device number 0 to leave a channel unassigned). The 'Device Control Setup OK' button will be deselected until all these conditions are met. Click the 'Check Configuration' button to insure that LabHelper recognizes any changes.
KEYBOARD SWITCHING (WITH TIMER). This is similar to manual keyboard control, except that
the computer automatically switches back to sampling after a specified reference
interval has elapsed. Accordingly, you must specify a reference interval
in addition to the reference device and sampling device.
SWITCH TO REFERENCE AT START AND FINISH
OF RUN. The computer
turns on a reference device for a designated period (the reference interval)
at the start of a data collection run, then switches to a sampling device
for most of the rest of the run. At the end of the run, the sampling
device is switched off and the reference device is switched on for a time
equal to the reference interval. [Two sampling devices are switched
on simultaneously if the 2 Device Group option has been selected.]
If this mode is selected, the user must designate (1) a reference device from the panel in the middle left of the screen, (2) a sampling device from the panel at the bottom of the screen, and (3) a reference interval > zero, entered in the edit field in the upper right of the screen. Note that only the FIRST sampling device selected will be switched, so select 1 only. Sampling devices are assigned to particular data channel(s) by entering the appropriate device number for the correct channel in the blue edit fields at the bottom left of the screen (select device number 0 to leave a channel unassigned). The 'Device Control Setup OK' button will be deselected until all these conditions are met. Click the 'Check Configuration' button to insure that LabHelper recognizes any changes.
PERIODIC REFERENCE, ONE OR MORE CHANNELS. LabHelper switches on the reference device(s) for
a reference interval at the beginning of a run, then steps sequentially
through a series of sample devices. The first sample device in the
sequence is switched on for a time equal to the sequence interval.
At the end of this interval, the reference devices are switched on for a
time equal to the reference interval. Then the next sample device
is turned on for a duration equal to the sequence interval, and the process
continues. When the last sample device has been selected and switched,
the cycle is repeated. This scenario continues until the data collection
run is complete.
The 'paradigm' for this mode is switching several different air streams through a single set of gas analyzers. Note that whenever a sample device is switched on, among the data channels which have sample devices assigned to them only the channel(s) assigned to the currently selected sample device(s) will record data. The other channels with assigned sample devices will register zero volts. Thus an assigned channel only records data when its assigned sample device is selected and operating. All non-assigned channels record data at all times, and all channels (including channels with assigned sample devices) record data during reference intervals. [2 reference and 2 sample devices are switched on simultaneously if the 2-group option has been selected.]
If this mode is selected, the user must designate (1) reference device(s) from the panel in the middle left of the screen, (2) one to seven sampling devices from the panel at the bottom of the screen, (3) a reference interval >0, and (4) a sequence interval > 0, which must be entered in the edit field in the upper right of the screen. Sampling devices are assigned to particular data channel(s) by entering the appropriate device number for the correct channel in the blue edit fields at the bottom left of the screen (select device number 0 to leave a channel unassigned). The 'Device Control Setup OK' button will be dimmed (deselected) until all these conditions are met. Click the 'Check Configuration' button to make sure that LabHelper recognizes any changes.
START & END, SEQUENTIAL FILES. This mode resembles the periodic references mode,
except that each external device is associated with a separate file
instead of a separate channel. A single channel (in the example
below, channel 1) is switched among several external devices. The
computer records one file from the first sample device (with references
at the beginning and end), then records another file from the second sample
device, and so forth until all assigned sample devices have been used and
the cycle repeats. In the example below, device 1 is the reference
device, and the sample devices are 2, 3, 5, and 7. When this mode
is selected, the autorepeat option is switched on by default.
If this mode is selected, the user must designate (1) a reference device from the panel in the middle left of the screen, (2) at least one sampling device from the panel at the bottom of the screen, and (3) a reference interval > zero, entered in the edit field in the upper right of the screen. The 'Device Control Setup OK' button will be deselected until all these conditions are met. Click the 'Check Configuration' button to insure that LabHelper recognizes any changes.
The bottom section of the device control window looks like this when switched to sequential files mode. There is a select button for each logical channel, and a numbered button for each possible external device (6 for the ADC-1; 8 otherwise):
In this example, there are three logical channels and
channel 1 is sequentially switched between 4 different external devices.
Devices 1, 3, 5, and 6 are recorded from on sequential files (another device
is used for reference).
In order to facilitate correct identification of a recorded file with an assigned device, the computer will add a prefix to the "comments" string saved with Warthog format files. The default prefix is "device 1", "device 2", etc, but you can assign any identifier you wish (with a maximum length of 20 letters). This window -- opened automatically whenever you access the External Devices window in Sequential Files mode -- allows customization of the identifier strings. You can also access this window from the Options window. Here is an example:
During data acquisition in either Switch to Reference at Start and Finish of Run mode or Periodic Reference mode, the operator can manually switch between the reference device and the current sample device by hitting the '-' or '+' keys, respectively.
When the information in the EXTERNAL DEVICE CONTROL
window is satisfactory, click the 'Device Control Setup OK' button
to return to the Display Setup window.