Automatic Brake Light Manufacturing and Welding Manual

This article is aimed at users with welding experience. Novice users are advised to purchase finished products directly.

 

Tools Required:

Multimeter, electric soldering iron, heat gun, tweezers, rosin water, solder paste, solder wire

 

Steps:

1. Welding power supply

This part of the circuit is located on the left side of the PCB board. Please solder according to the schematic diagram. There is no requirement for the soldering order of this part of the circuit. Generally, there will be no problem if you are bold and careful. Note that the positive and negative poles of the capacitor must be correct. The end with the dark line on the capacitor must be aligned with the end with the rounded corner of the wire frame on the PCB board. After soldering, connect the circuit board to a 3V power supply (the V and G marked on the lower left corner of the PCB board is the power interface). Be careful not to connect the positive and negative poles in reverse: V to the positive pole and G to the negative pole. After the power is connected, use a multimeter to measure one pin of LED1. There should be a 3.3V voltage output.

 

Schematic diagram:

The effect after welding is completed is as shown in the figure:

2. Welding acceleration sensor

 

Since the pins of the acceleration sensor chip are all on the bottom, solder paste and a hot air gun are required for soldering. This step is the most difficult in this production (for a more detailed soldering process, you can search "manual soldering QFN" on Google to find some detailed graphic tutorials). First, make sure the pad is clean. You can use alcohol to wipe the pad; then carefully apply a little solder paste on the pad. Make sure there is solder paste on each contact and not too much solder paste. The PCB board after applying solder paste is as shown below:

  

Then carefully place the chip on the pad (there is a small white dot on the chip indicating the No. 1 pin of the chip. When placing the chip, it should correspond to the No. 1 pin corresponding to the small white dot on the PCB board), and press it gently with tweezers. Then adjust the hot air gun to about 360 degrees, and blow the chip with the largest nozzle and the smallest air volume. When the solder paste melts, you can see that the chip automatically aligns with the position of the pad under the action of the liquid surface tension, and then heat it slightly. Note that the PCB soldered with a hot air gun is very hot, and it should be left for a while before moving the PCB board.

 

Finally, I attach a screenshot of the PCB. Note that pins 1 and 6 are power supplies and should be connected; pins 2, 4, and 5 are grounds and should be connected. The other pins are not connected to each other (power and ground cannot be connected). After using a multimeter to confirm that there is no short circuit, you can proceed to the next step. (If there is a cold solder joint, you can use a soldering iron to dip a little solder to repair it; if there is a short circuit, you can only use a blowgun to remove the chip and re-solder it). [page]

 

PCB diagram, used to check welding quality:

The effect after welding is completed is as shown in the figure:

3. MCU welding

 

The pins of MCU are relatively small, but it is still relatively easy to solder after mastering the method. Rosin water is needed in this step, but it cannot be applied directly to the pad, because it will become very sticky after drying, which is not conducive to the positioning of the chip. First, use a soldering iron to tin the outermost pad, then place the MCU and solder the tinned pins with a soldering iron. If it is skewed, you can continue to use the soldering iron while heating and adjusting the position (when placing the MCU, pay attention to the position of pin No. 1. The small white circle on the PCB is marked as pin No. 1, and the black circular depression on the MCU is marked as pin No. 1). After the MCU is placed straight, use a soldering iron to dip a little solder and solder another pin for fixing. After the MCU is fixed on the pad, moisten the remaining pins of the MCU with rosin water, wait for the rosin water to evaporate, dip a little solder with the soldering iron, and gently touch each pin of the MCU until all pins are evenly tinned and stick to the pad. If there are stuck pins, don't panic. Use a soldering tape or ordinary copper wire, stick a little rosin, and then put it on the stuck pins and heat it with a soldering iron to let the excess solder be taken away by the soldering tape. Finally, use a soldering iron to confirm that there is no short circuit on each pin, and then solder the other resistors and capacitors according to the schematic diagram.

 

Schematic diagram:

 

The effect after welding is completed is as shown in the figure:

4. Welding of LED lights

 

There is basically no difficulty in soldering LED lights. Just be careful not to stick the LED pins together. Please use a multimeter to confirm the positive and negative poles of the LED. The direction of the current flowing through the LED on the PCB should be from the end with the missing pin to the other end. For the resistance value of the current limiting resistor, it is recommended to use the value recommended in the schematic diagram (that is, 300 ohms for blue LEDs and 470 ohms for other color LEDs). After testing, the recommended value can basically achieve the best match between brightness and current.

 

Schematic diagram:

 

 

5. Power on

 

After the circuit is made, you can turn on the power. Before turning on the power, you need to confirm two points: 1. The power supply and ground are not short-circuited; 2. The power supply and ground are not reversed. After confirming that there are no problems with these two points, you can turn on the power. If the power is normal, you can use a cable tie to tie the circuit board and the battery box together to complete the hardware production.

 

 

6. Burn the firmware

The last step is to write the firmware into the device. There are two ways to write the firmware: 1. Use the serial port; 2. Use the SWD interface

Using the serial port:

1. Install the USB to serial device on the computer, and install the driver and STM update program. //TODO, provide driver and update program links.

2. Connect the serial port converter and the automatic brake light PCB. Note that the automatic brake light serial port is 3.3V level, please adjust the voltage of the serial port converter to 3.3V (through jumper or switch).

3. Short-circuit the two contacts marked UPDATE on the PCB. (Use a resistor foot or tweezers or something like that)

5. Run the STM update software on the PC and select the firmware to be downloaded. //TODO, provide the compiled firmware download address

4. Turn on the device power and wait for refresh.

Using the SWD interface: