|Authors||Sherry Miller Hocking; Brewster, Richard; Peer Bode; Hank Rudolph; Matthew Schlanger|
A sequencer is a multi-input device which switches from one input to another automatically. The number of inputs and rates of switching vary with the device. There are two basic devices in the system, the Jones 8 Input Sequencer and the Four Channel Sequencer.
Jones 8 Input Sequencer
The Jones Sequencer is an eight input, one output voltage controllable switcher. It uses three different methods of control for selecting the input and presenting it to the output. The first method, or the "sequence" control mode, will step through the channels (numbered 0-7) in numerical order using a 2 to 8 step pattern and then repeat this pattern indefinitely. In this mode the inputs are always presented in the sequential order that is selected at the matrix. A second method, the "binary" control method uses a three bit binary system to select the order of the channels, allowing more complex and possibly non-repeating patterns of switching to occur. In the third mode, the device is operated as a manual switcher.
When using voltage control, the rate of the sequence, as determined by an external clock such as an oscillator, can range from extremely slow with vertical interval switching, up to several multiples of the horizontal frequency which allows juxtaposition of signals within divisions of the raster.
Although the sequencer is mainly used as a video signal processor, another application of this device is to switch among 8 separate signals using the mini-jack inputs and outputs on the front panels. These signals must be within the range plus/minus 5 volts and can be control voltages, audio signals or oscillator-generated shapes. The device is compatible with the Analog Control system in the Image Processing system as a signal processor or signal generator.
How to Use the Sequencer
The numbers in parentheses indicate the controls on the front panel of the sequencer, shown in Figure 1.
Manual Control in the Switcher Mode
Select the video inputs to each channel at the matrix. Select the method of sequencing. Start with switch (1) in the down position, marked "switcher". Set control (2) in the down position, marked "switch". This allows manual control.
In this mode the pushbutton controls allow you to choose each channel individually in any order. The corresponding lights, or LEDs, will indicate which signal is being sent to the output.
Output Pedestal (8)
Adjust the pedestal control knob for the video output.
Channel Pedestals (10)
Step through each channel and adjust the pedestal control knobs for each input.
Vertical Interval Switching
Sync Input (4) and Sync Modes (3)
For vertical interval switching (VIS) a sync source and sync mode need to be selected. The sync input (4) requires vertical drive, usually patched from the output jack marked "V.D." on the Analog Control System. For manual control in the "switcher" mode, set the sync mode select (3) to the "1" position to allow vertical interval switching.
Set the sequence/switch switch (2) to sequence, or the up position. The binary/switcher switch (1) will not function. Select the number of steps in the sequence. In this position the pushbuttons (9) will select what the last channel in the sequence will be, before returning to channel 0. Remember that selecting channel 5 makes it a six step sequence.
Count Input (5)
Patch the output of an oscillator into the input mini-jack marked "count". This sequence will divide the frequency of the incoming signal in half. That is, the rate of the sequence will always be twice as slow as the original signal from the oscillator.
Sync Modes (3)
Select the sync mode according to the sequence rate in the following way:
Below 60 Hz
For rates which are below 60 Hz, or the field rate, sync modes "1" or "2" can be used. As the control voltage approaches 60 Hz, the sequence rate will behave differently within these two modes. In sync mode "1", harmonics between the sync and count pulses will occur causing the rate of switching to actually slow down as the "count" pulse approaches the 60 Hz threshhold. In sync mode "2", no harmonics will occur, and the sequence rate follows the count pulse accurately up to the threshhold. Neither mode will allow rates of switching above 60 Hz.
Above 60 Hz
Sync mode "0" will allow signals greater than 60 Hz or field rate as the count pulse. This will divide the raster and permit switching within the frame. Rates right above 60 Hz will yield horizontal bars, presenting each input in succession from the top to the bottom of the screen. To lock these bars, vertical drive must be applied to the sync input of the oscillator which is acting as the external clock because this module can accept much higher frequencies than the four-channel sequencer. Combinations of externally syncable oscillators can be mixed together to create shapes, such as boxes and used as the count input. This will yield a variety of multiple splitscreen images.
In sync mode "3", the sync input becomes the clock pulse. With vertical drive patched into the sync input, the rate of switching will always beat 60 Hz.
BINARY CONTROL MODE
Binary Control A, B and C (6)
Set switch (2) in the down or switch position. Set control (1) in the "up" position, marked "binary control". In this mode the sequencer uses binary logic to choose which input is sent to the output. The controls are three twoposition switches with corresponding voltage control inputs. The controls represent 3 bits of data, in which there are 8 possible combinations of onoff positions. Figure 2 is a table which shows the relationship of these on-off positions to the channel numbers of the sequencer. "Switch C" is the least significant bit. "Switch A" is the most significant bit. 0"indicates the off or down position, and "1" indicates the on or up position.
Control Voltages and Sync Modes (3)
Control voltages can be applied to one, two or all three of the input jacks simultaneously. Signals going into the "count" input (5) have no effect in the binary control mode. Figure 3 uses an example in which 3 asynchronous pulse waves are being patched into jacks A, B, C respectively. Lines 1, 2 and 3 show their waveshapes in respect to time, line 4 shows the resulting binary number and line 5 shows which channel number is being sent to the output for each period of time.
Below 60 Hz
For control voltages below 60 Hz, sync mode "1" and vertical drive patched to the sync input will allow vertical interval switching.
Above 60 Hz
Sync mode "0" will allow control voltages above 60 Hz. Figure 4 shows the output of three externally synced oscillators displayed on the raster. The first and third are at frequencies above the horizontal and the second above the vertical rate. The fourth image shows the division of channels within the raster when these three oscillators are applied to binary control inputs A, B and C respectively.
The binary input control can also accept combinations of control voltages above and below 60 Hz. Figure 5 shows an example in which 2 oscillators, combined to generate a box shape, are applied to input B. A second slow varying control voltage is applied to input C. When the second control voltage is low the combination of channels 0 and 2 is seen. When the voltage is high, the combination of channels 1 and 3 is seen. Note that for this application, either mode "0" or "2" must still be used. In order to have vertical interval switching for the slower control voltage, it must be patched into a sample and hold module beforehand, with vertical drive as the clock input.
SWITCHING OF PLUS/MINUS 5 VOLT SIGNALS
Finally, an alternative use of the sequencer is to step through or switch among a set of plus/minus 5 volt signals. In this application, the input jacks (11) can take in a plus/minus 5 volt signal (for audio, control voltage or shape) at each channel. These are accessed at either of the plus/minus 5 volt output jacks (7). With no inputs to these jacks the module can still step though a series of eight DC control voltages which are preset with the pedestal control knobs (10) of each channel. All three modes of switching can be used and triggers can be sent to the sync input (4) for synchronizing a number of control voltage events in time.