I am only able to work with AB systems, so unfortunately I cannot convert it for you. However, I want to mention that the current setup may not function as expected. To maximize efficiency, consider accounting for different coin denominations like $1, $5, or $10. Currently, the logic only accounts for $1 coins being inserted, even if a larger denomination is used. By simplifying the code and focusing on one section to handle the lights based on the total amount, the program will run smoother. Ensure to update the total amount when coins are inserted and subtract the amount when a product is selected. This will ensure the lights operate correctly. Moving forward, it's important to implement a verification system to confirm that enough money has been inserted before a product can be selected. This step will prevent unauthorized users from pressing buttons without proper payment.
Is the specification poorly written? Could it be a translation issue? Have you listed all the inputs and outputs? Does the machine only accept $1 coins, or does it also take $5 and $10 coins? Is there a change dispensing feature? It appears that Seven Up is $1, Cola is $5, and Evian is $10. Is this accurate? I don't see any mention of calculating the RemainingAmount.
If you have experience in programming languages like Python, C, Pascal, or Java, it's likely that you may not fully grasp the concept of PLCs. PLC programming revolves around the scan cycle, which functions as the clock in the system. Understanding the scan cycle is crucial for ensuring the effectiveness of your ST code. The scan cycle can be visualized as the PLC executing your code repeatedly, with each line being processed multiple times per second. This means that actions within your code, such as adding coins to update a total amount, are executed at very rapid intervals, often every 10ms or less. For example, if a coin sensor detects a coin for 100ms, the total amount will be incremented multiple times within that period, highlighting the importance of the scan cycle in PLC programming.
To improve your understanding, consider the revised code snippet below, which demonstrates the proper handling of inputs, outputs, and logic in a PLC environment:
```
// Add coins and update the total
IF I0.0 AND NOT I00_memory THEN // Single $1 COIN_INPUT
TotalAmount := TotalAmount + 1;
END_IF;
I00_memory := I0.0; // Coin insertion is a one-shot event!
// Light Logic
Q0.0 := TotalAmount > 0; // Light Seven-Up ON
Q0.1 := TotalAmount > 4; // Light Cola ON
Q0.2 := TotalAmount > 9; // Light Evian ON
// Beverage Selection
IF Beverage_Selected = '' THEN
IF I0.1 THEN Beverage_Selected := 'Seven-Up';
ELSIF I0.2 THEN Beverage_Selected := 'Cola';
ELSIF I0.3 THEN Beverage_Selected := 'Evian';
END_IF;
END_IF;
// Beverage Dispensing Logic; I0.4 cancels dispensing
Q0.3 := Beverage_Selected = 'Seven-Up' AND Q0.0 AND NOT I0.4;
Q0.4 := Beverage_Selected = 'Cola' AND Q0.1 AND NOT I0.4;
Q0.5 := Beverage_Selected = 'Evian' AND Q0.2 AND NOT I0.4;
Timer_1(IN:=Q0.3 OR Q0.4 OR Q0.5, Expired=>Expired);
IF Expired THEN
IF Q0.3 THEN TotalAmount := TotalAmount - 1; END_IF;
IF Q0.4 THEN TotalAmount := TotalAmount - 5; END_IF;
IF Q0.5 THEN TotalAmount := TotalAmount - 10; END_IF;
END_IF;
IF Expired OR I0.4 THEN Beverage_Selected := ''; END_IF;
```
By implementing this code structure and considering the implications of the scan cycle, you can enhance the functionality and efficiency of your PLC programming.
During my time in the gaming industry, I gained experience working with different types of coin mechs. Some were mechanical, guiding coins down different tracks based on their size and composition. Others were electronic, electronically verifying the coin and adding its value to the total amount. It was crucial for these mechanisms to be oneshots, meaning the coin would only energize the input for a brief amount of time to prevent multiple counts being registered due to the PLC scan time. Take a closer look at Brian's code and observe how oneshots are utilized for the coin input, showcasing its efficiency and cleanliness.
In a forum thread, user Rsflipflop256 proposed a trade: ladder training in exchange for structured text. How about we convert this into a ladder logic diagram?
Here is the ladder logic diagram:
Initialization of variables and transition to Idle state (S0):
- When COIN_INPUT is triggered, add the amount to TotalAmount
- Light Seven-Up turns on when TotalAmount is greater than or equal to 1
- Light Cola turns on when TotalAmount is greater than or equal to 5
- Light Evian turns on when TotalAmount is greater than or equal to 10
- Selecting Seven-Up turns on Q0.3
- Selecting Cola turns on Q0.4
- Selecting Evian turns on Q0.5
- After 7 seconds, the beverage dispenser turns off
When there is remaining amount:
- Light Seven-Up turns on when RemainingAmount is greater than or equal to 1
- Light Cola turns on when RemainingAmount is greater than or equal to 5
- All lights turn off when RemainingAmount is zero
This ladder logic diagram outlines the process of selecting and dispensing beverages based on the amount inserted.
drbitboy stated that familiarity with other programming environments such as Python, C, Pascal, or Java does not necessarily translate to understanding Programmable Logic Controllers (PLCs). PLC programming is centered around the concept of the scan cycle, which serves as the clock for executing code. It is crucial to grasp the significance of the scan cycle in ensuring the functionality of code, as highlighted by experts like @MikeyNand@Steve Bailey.
To simplify, envision the PLC duplicating and executing your code continuously. This process involves converting output values to physical signals and updating input values, followed by the repeated execution of each line of code. Each line can be executed multiple times per second, highlighting the rapid pace at which PLCs operate.
For example, the statement "// Add coins and update the total" will be executed approximately every 10ms. Therefore, if the coin sensor I0.0 detects a coin for 100ms, the total amount will increment multiple times due to the scan cycle.
To improve coding efficiency, consider the revised code snippet provided below:
- Condition set for single $1 coin input.
- Light logic for different beverage thresholds.
- Selection logic for choosing beverages.
- Dispensing logic with cancellation capability.
- Timer implementation for dispensing control.
Understanding the scan cycle's role in PLC programming is vital for achieving the desired functionality.
Kkklll pointed out that many people make a common mistake in Ladder Logic Programming known as "duplicate destructive bits." This mistake occurs when two separate coils in the program write a value to the same bit, resulting in one coil overwriting the value written by the other. This issue is highlighted in red in the code provided. The solution to this problem involves ensuring that the program does not write conflicting values to the same bit.
Furthermore, the code fails to decrement the TotalAmount variable when a drink is dispensed, only incrementing it when a coin is dropped. To address this issue, it is suggested that the TotalAmount variable should be decremented when a drink item is dispensed based on the selected beverage.
Additionally, the code contains multiple rungs that initiate the dispensing of drinks by starting a timer based on specific conditions. However, the code lacks a comparison of TotalAmount to verify if there is enough money deposited to pay for the selected drink. This omission could lead to errors in the dispensing process.
Moreover, there is a lack of clarity in the code regarding the purpose of button I0.4, which appears to control the lights Q0.0, Q0.1, and Q0.2. It is recommended to combine the logic for controlling the lights with the testing of I0.4 and TotalAmount variables to improve the efficiency and readability of the code.
In conclusion, addressing these issues will ensure that the code functions correctly within the PLC's repeating scan cycle. It is essential to follow good programming practices to optimize the performance and reliability of the vending machine's control system.
Kkklll mentioned that they would like to understand each explanation in detail, but due to time constraints, they are seeking help here. However, it is important to acknowledge the consequences of requesting a ladder logic program without the ability to create one oneself. This can be seen as plagiarism, which may have serious implications. It is evident from the ST code provided that there is a lack of experience in programming languages. Therefore, it is essential to take the time to learn and understand the material rather than just seeking a quick solution. Failing to do so may lead to potential risks and issues down the line, affecting not only oneself but also others in the workplace. Remember, your lack of planning does not make it an emergency for others. It is crucial to invest time and effort into learning the necessary skills to avoid any potential harm or misunderstandings in the future.
There may not be a direct translation of all functions from ST to ladder logic. However, by gaining a thorough understanding of both, it becomes possible to replicate functions in a different language. Assistance is readily available for those looking to learn and excel in PLC programming. Mastering ST as a novice PLC programmer is commendable, as everyone starts from a point of inexperience when embarking on programming endeavors.
A well-crafted program not only performs essential functions but also anticipates and manages various scenarios, even those that may seem unlikely. For instance, in a vending machine scenario where the maximum price is $10, any excess coins should be rejected. The program must account for different user behaviors, whether they are extremely naïve, cunningly ingenious, or a combination of both.
It is crucial to strive for a deep understanding of ladder logic and its application. Resources like the "Patterns of Ladder Logic Programming | Contact and Coil" video can serve as valuable starting points for mastering ladder logic concepts.
In programming PLCs, precision and attention to detail are paramount. A slight oversight, such as failing to update a product designation from Product1 to Product2, can lead to significant operational errors. It is essential to ensure that the program executes according to the intended specifications and functionalities to avoid undesirable outcomes.
By meticulously developing and refining programs, incorporating necessary checks and balances, one can ensure that the PLC executes commands accurately and efficiently, leading to seamless operations and desired outcomes.
My program fragment does not meet the specified requirements as I overlooked them and assumed that automatic change dispensing after vending was the correct approach. This oversight was my fault for not paying attention, resulting in additional work for myself. If this were a real job, this mistake could have caused more complications. Fortunately, my goal was simply to create a basic ladder logic example.
One improvement that could be made is renaming the input button to DispenseSelect. If this button is actually implemented, it should be debounced and/or one-shotted for proper functionality.
In Rockwell PLCs that utilize this code, physical inputs and outputs are typically referenced only once and then mapped to a tag for use throughout the program. This helps avoid issues with inputs changing state between references during the program scan. While older controllers updated I/O status between scans, newer models like ControlLogix and CompactLogix operate asynchronously.
For more detailed information, there are workarounds available using priority settings in older CompactLogix systems. An example of a common mistake is the presence of duplicate destructive bits, as seen in the Product2 scenario. The program logic turns on Product1.DispenseEnable if there is at least $1 credit, but then turns it off if there is only $4, causing inconsistent behavior. This could lead to a customer needing to insert at least $5 to buy a $1 drink.
When expanding the program, the OneSecondPulse is only active for a single program scan, rendering ChangeDispense1 ineffective for directly controlling a solenoid. To address this, a latch with a timer may be used to fire the solenoid for a brief duration. Similar programming techniques would be applied for dispensing drinks through solenoids or motors.