Thermal printers are very common in our daily life, and there are examples of thermal printers in restaurants, parking lots and shopping. This article will focus on the application of thermal printers in parking systems.
Materials To Be Used
- STONE STWI101WT-01
- FTP thermal printer head
- Raspberry Pi pico
- Coin-operated machine
The control function is displayed on the serial screen, the main interface selects the floor, after entering the main interface selects the parking space, at the same time it will display the parking space number in the text box on the top right, then selects the stay time, it is two scrolling text selectors, then also the same will display the order information in the text box on the top right, according to the fixed unit price which multiplies with the stay time to get the total price. Then only when the parking space and the stay time are selected, you can go to the payment button, otherwise, it is invalid. After entering the payment screen, a coin acceptor will be used. Then the screen will show the number of coins to be put in and the number of coins already put in. After the coins have been put in, a payment success message will be displayed. Then you can choose to print a small ticket to print the place number and time on the thermal paper.
The Design Process
At first, I wanted to use the Raspberry Pi pico to make a small printer. Then in the process of selecting components, I think the thermal printer is more convenient to achieve, after determining the program, I began to purchase hardware. In fact, in the process of online procurement, I found that there are many thermal printers with good driver circuits, most of them are made by using STM’s chip, and they are designed with their own set of instructions. For example, by using his instructions to let the printer print characters or go paper, but this printer’s practicality is very high, but there is no value in learning. It is to send instructions through the serial port on the line, you can manipulate the printer. So I thought I’d buy a print head and develop it myself. Then about the print head, I chose an FTP thermal print head.
This print head should be available internationally, the basic principles are similar. The left side is a stepper motor. Then the middle head is 6 heating units. Each heating unit has 64 heating points on it. So a total of 384 heating points. Then below is a latch. Below the latch is a shift register. Finally, there is a clock signal to be provided. So the whole principle of operation is to provide a clock signal to the print head and then send data every clock period, after sending 384 clock signals and 384 data, the data in the shift register will be stored in the latch. Then the latch is set to a low level. Then the 384 heating points will choose to heat or not to heat according to whether each data is 0 or 1. At the same time, let the stepper motor rotate to drive the thermal paper to design the desired character.
After I got the thermal print head, I went ahead and asked for a datasheet and it was a 30pin FPC cable. So it’s obviously not very convenient to connect to the pico directly with it. So I thought I’d better design a backplane circuit.
I have a STONE serial screen is a 12v power supply, and then I look at the thermal print head printing voltage of a reference value is 7.6v, the maximum value is 8v, then provide it with a voltage of about 7.6v. It also has a logic voltage is 3.3v, and then the Raspberry Pi pico maximum support 5v power supply and it has a 3.3v output voltage, then the power supply design can use two dcdc, with 12v power supply, one dcdc output 7.6v to power the thermal print head, the other dcdc output 5v to the pico, and then use the 3.3v from the pico to power the thermal print head logic voltage. Then 12v leads the way directly to the serial screen.
By the way, the stepper motor for that thermal print head also needs to be driven. I have an integrated Darlington tube integrator. But it’s too big, and it’s a straight plug-in, so just buy a driver chip. Then this aspect of the drive motor is also OK.
Printing requires the design of the font, basically, everyone is using spin flash for font storage, which is a huge project. Only ASCII code is more than 100, so you need to buy another SPF flash. Then the whole planning is almost like this.