Design and implementation of a new data recording system control scheme

Abstract: A new data recording system design is proposed and applied in the transformation of the AsKania data recording system. It mainly describes the hardware and software implementation of the dot matrix control module and the dot matrix driver module in the transformation of the AsKania data recording system, as well as the problems solved in the implementation of the scheme. After practical verification, the feasibility and reliability of the scheme are proved, and the uniformity of the dot matrix is ​​improved.

Keywords: camera, dot matrix, uniformity, anti-cross-light

The high-speed camera is an optical measurement device used for the trajectory and attitude measurement of rockets in the shooting range. The electronic control system of the high-speed camera is mainly composed of synchronous control, data recording, automatic dimming and other systems. Under the control of the photography time system and photography frequency, the target and related information are recorded on the film in real time and clearly, providing original data information for post-processing.

Data information is recorded on film in the form of dot matrix. The traditional data recording system collects, processes and arranges information such as azimuth, elevation, time, photography frequency, synchronization signal, photography code, station address, and bullet sequence synchronously under the control of photography timing system. Finally, the dot matrix is ​​dotted row by row or column by column in a time-sharing scanning manner under the control of photography frequency to record the information on the film. If some points on the film are underexposed due to insufficient dot matrix brightness or other reasons, it may cause misjudgment or misjudgment when the reader is used later, which will eventually lead to incorrect data processing results. Using traditional methods to increase the brightness of underexposed points will also make other points in the same row or column of the point brighter, resulting in unclear edges between points, which will also affect the interpretation. Even so, sometimes the brightness of some underexposed points still cannot meet the interpretation requirements.

Based on the above problems, the author proposed a new design scheme to control the lighting time of each dot matrix separately to achieve single-point control of dot matrix exposure time. This scheme was implemented in the modification of AsKania KTH532 film theodolite.

AsKania KTH532 high-speed camera was designed and manufactured by France in the 1970s. The dot matrix of its dot matrix data recording system is a 5×22 LED array, with LED as the light source, and data recording is completed by optical fiber transmission and projection onto film. If the traditional control method is used, the uniformity of the dot matrix produced by this dot matrix and projection system is extremely poor, and the reader cannot process the data. The main reasons are:

(1) Using LED as the light source, the brightness is uneven due to differences in its own parameters;

(2) The optical fiber in the original optical projection system is aged and broken. During the transmission process, the optical projection system attenuates the light energy of each point on the dot matrix differently. Even if the illumination of each point is the same, it cannot guarantee that the intensity of each point projected on the film is the same, so it is impossible to produce the same exposure on the film, that is, the blackness of the points is different, and the difference is large, and the dot matrix is ​​uneven as a whole.

Due to structural reasons, this method must be used when the data recording system is modified, and the original optical projection system must be retained. The traditional control method cannot solve the problem of insufficient and uneven dot matrix blackness caused by the above reasons. Therefore, in the transformation of the dot matrix data recording system, a single-point control scheme of the dot matrix exposure time is used, so that the exposure time of each dot matrix can be set by programming, which greatly improves the uniformity of the dot matrix.

1 Principle and composition of the data recording system

The principle and composition of the data recording system are shown in Figure 1.



The data recording system is mainly composed of a host computer, a data acquisition module, a dot matrix control module, a dot matrix drive module, a dot matrix module, and an optical projection module.
Data acquisition module: The data acquisition module realizes the acquisition of dot matrix information. It is mainly a lower computer with an 8031 ​​single-chip microcomputer as the core. Under the control of the photography time system, it collects time, azimuth, pitch angle, synchronization information, frequency encoding and other information one by one in real time, and then stores them in the dual-port RAM for the host computer to read through the bus.

Host computer: Arrange the data information in the dual-port RAM through the bus according to the required dot matrix arrangement format, and program the lighting time of each dot, and finally output it line by line by the dot matrix control module.

Dot matrix control module: Under the control of the host computer, according to the exposure time set by the host computer for each dot, as well as the lighting and extinguishing of the dot, the dot matrix control signal is output row by row to the dot matrix drive module.

Dot matrix drive module: The control signal output by the dot matrix drive module cannot directly drive the LED of the dot matrix. The drive module generates a drive signal to drive the LED of the dot matrix.

Optical projection system: The light energy of the dot matrix LED is transmitted to the film, so that the film is exposed and the data is recorded.

The main difference between the dot matrix single-point control scheme and the traditional control scheme lies in the different dot matrix control modules. The following mainly introduces the software and hardware design and implementation of the control module and the drive module in the dot matrix single-point control scheme.

2 Hardware design and implementation of control module and drive module

The traditional dot matrix control and drive modes are:

(1) One-time lighting. That is, each LED cathode and anode have a control signal respectively, and a dot matrix is ​​lit at one time. This method takes the shortest time, but the control circuit and drive circuit are very complicated and are generally not used.

(2) Column-by-column scanning. Column-by-column scanning means lighting one column each time, and a dot matrix is ​​lit in 22 times. This method is simpler than the circuit of lighting up once, but it takes longer than lighting up once.

(3) Line-by-line scanning. Line-by-line scanning means lighting up one row at a time, and a dot matrix is ​​dotted in 5 times. This method has the simplest control circuit and drive circuit, and the time it takes is between the previous two. This method is generally used.

Use line-by-line scanning mode. In order to ensure the blackness and uniformity of the dot matrix on the film, if the traditional blackness adjustment scheme is adopted, there are the following problems: ① Reduce the value of the current limiting resistor in series in the LED, so that the driving current passing through the LED increases, thereby increasing its brightness and the blackness of the light dots on the film. However, on the one hand, in the AsKania KTH532 dot matrix system, the optical projection system has more broken wires, and the process of projecting the dot matrix onto the film causes a large loss of light energy. Simply increasing the brightness will affect the life of the LED, and the brightness within the limit current range is not enough to compensate for the energy loss caused by some broken wires; on the other hand, because the line-by-line scanning method is selected, adjusting a column of current limiting resistors will affect the brightness of 5 dots, so this method is not advisable. ② Extend the lighting time of the LED, that is, extend the exposure time, and increase the blackness of the light dots. Also, because the progressive scanning mode is selected, adjusting the lighting time of a row will affect the brightness of 22 dots. The dot matrix control circuit designed in this scheme can control the driving signal of each dot of the dot matrix through programming, realize single-point control of the exposure time, and thus realize the adjustment of the blackness of the single dot to ensure the uniformity of the dot matrix.

The 22 columns of the dot matrix are correspondingly controlled by 22 82C54 timers. Since the scheme uses the progressive scanning mode, the 22 82C54 timers control each dot of the 5-row and 22-column dot matrix in a time-sharing manner. 82C54 is a programmable subtraction counter, which has six different working modes. Among them, mode 1 (programmable monostable characteristic) outputs a single-shot negative pulse signal, and the pulse width can be set programmably to meet the requirements of the hardware circuit. Its timing is shown in Figure 2. After setting the working mode and writing the count value, the output terminal outputs a high level; when the trigger signal rises to a high level, the output is a low level and starts counting; when the counter is reduced to zero, the output is a high level. The width of the negative pulse output by the timer is determined by the count value of the timer.



In this scheme, the column selection signal is used as the trigger signal of the timer, and the timer output is the column control signal. The strobe time of the 22 columns of LED in the dot matrix is ​​controlled by 22 timers respectively. The dot matrix control signal is driven inversely to generate a column drive signal. When the row control and column control are both effective, the LED is lit. The dot matrix drive circuit is shown in Figure 3.




If it is a bright spot, the column selection signal is "1", triggering the timer count, the control signal output by the timer is "0", the drive signal is "1", and the LED array can be lit after the row is selected; if it is not bright, the column selection signal is "0", the control signal output by the timer is "1", and the drive signal is "0". Even if there is a row selection signal, the LED cannot be lit.

By changing the count value of 8254, the width of the negative pulse of the column control signal can be changed, that is, the time to drive the column to light up can be changed (the size of t in Figure 4). This method can avoid the use of complex control circuits and drive circuits, and at the same time realize the single-point control of the dot matrix brightness and the adjustment of the single-point blackness. The timing and waveform are shown in Figure 4.





3 Design and implementation of control software

After the system is powered on, the program is initialized first, and then the exposure time of each point in the dot matrix is ​​programmed according to the different LED brightness and the broken wire situation of the optical projection system, that is, different count values ​​are assigned to the corresponding timer. Under the control of the photographic frequency, the dot matrix has a dot matrix corresponding to each picture, so data acquisition, processing and arrangement are carried out after the rising edge of the photographic frequency arrives. Finally, the arranged dot matrix is ​​output in a row-by-row scanning mode to control the drive module and light up the dot matrix. After scanning one frame, after judging the falling edge of the photographic frequency, the data acquisition and control of the next dot matrix are prepared. In this way, on the one hand, it prevents multiple exposures of the dot matrix on the same picture, and on the other hand, it ensures the real-time data recording on each picture. The software flow chart is shown in Figure 5.



4 Anti-cross-light measures

In practice, in order to reduce failures, the hardware circuit is simplified as much as possible. The dot matrix control hardware circuit is designed as follows: for each row scanned, the 22 timers corresponding to each column are triggered simultaneously. This brings a problem: since 8254 is a subtraction counter, its minimum count value is 1. For the points that do not need to be lit, even if the count value is the minimum, the timer will have a negative pulse output, corresponding to the generation of a driving signal for an LED dot matrix. After the row is selected, the LEDs that do not need to be lit in the dot matrix are lit, and finally the exposure or cross-light phenomenon is generated on the film, resulting in misjudgment when the dot matrix is ​​read afterwards. In order to eliminate this phenomenon, the following measures are taken:

(1) Hardware measures: add a photocoupler at the front end of the dot array control signal, and its delay time is much longer than one clock cycle, so that the sharp negative pulse signal output by 8254 is filtered out due to the delay of the photocoupler, and the corresponding column drive signal is low level. After the row is selected, the corresponding LED cannot be lit because there is no column drive, thus eliminating the occurrence of cross-light phenomenon.

(2) Software measures: when scanning the dot array row by row, first use the row selection signal to trigger 8254, so that the column control negative pulse output of the non-lit dot, and ensure that the column control level has been flipped to a high level before sending the row selection signal, so that the LED that should not be lit will not be lit.

The timing comparison of the dot matrix row by row scanning before and after the anti-cross-light measures are adopted is shown in Figure 6.





The above two methods can be used either or both. If only hardware measures are taken, a photocoupler with a sufficiently long delay must be selected; if only software measures are taken, it is only necessary to add a sufficient delay before the row selection if time permits.

After being modified and applied in the AsKania data recording system, it has been proved that this scheme is effective in exposing points with more broken wires and greater light energy loss in the optical projection system, so that some points that hardly produce exposure using conventional schemes can have sufficient exposure, and the dot matrix quality fully meets the requirements of the reader.