Design of a vehicle combination switch detection device based on AT89S52

The automobile combination switch is a commonly used switch in automobiles (see Figure 1 for its appearance). It has low beam, high beam, low light, headlight, overtaking, high speed wiper, low speed wiper, intermittent wiper, washing, left turn, right turn and other gears. At present, many manufacturers still use the traditional simulation test method when testing combination switches. This method is prone to omission and misdetection of individual gears, and the detection efficiency is also low. For this reason, the author has made an automobile combination switch detection device based on AT89S52. The device can accurately detect all gears of the combination switch, and is equipped with sound and light alarm functions, which effectively prevents misdetection and omission of individual gears in simulation tests. Here, only the circuit part of the device is analyzed as follows.

Figure 1 Common switches

1. Overall design

Combination switch detection is a very important link in production. Generally, simulation detection is adopted, that is, all peripheral circuits of the combination switch are installed on the test bench, and the indicator lights are used to simulate the working conditions of each gear. For example, if the combination switch is pulled to the intermittent gear, the indicator lights should flash intermittently. This detection method has high requirements for workers and is very easy to cause false detection and missed detection. The combination switch detection device designed and produced by the author adopts the detection scheme of single-chip scanning, adds sound and light alarm, reduces the labor intensity of workers, effectively prevents false detection and missed detection, and is particularly suitable for use on the production site. The actual circuit is shown in Figure 2.

Figure 2 Circuit diagram

2. Circuit Design Principle

This detection device uses the common AT89S52 in the market as the MCU. The chip is easy to program, easy to download programs, and has a high cost-effectiveness. It is widely used in the field of industrial control. This detection device sets a qualified indicator light for ten gears and an overall qualified indicator light for a certain type of combination switch. The overall qualified indicator light will light up when all ten gears are qualified. In addition, in order to focus the workers' attention and prevent misjudgment, a special overall qualified sound alarm is set, and an alarm is sounded by voice when the overall qualified indicator light up.

1. Hardware Design

The hardware circuit of this detection device is shown in Figure 3.

Figure 3 Hardware circuit of the detection device

PO and PI ports are used as the input of the external leads of the combination switch. The external leads of the combination switch are the external leads of each gear switch. When the combination switch is turned to different gears, each lead is connected or disconnected as required.

P2 port and P3.0, P3.1, and P3.6 serve as qualified alarm indications. This is just a simple LED indication circuit. If the indication needs to be more obvious, a high-power drive display circuit can be added through the high-power indicator light extension port.

The P3.2 port is connected to an external probe switch. When the combination switch is pressed on the test fixture, the probe switch will be closed at the same time, and the detection device will start detection immediately.

P3.7 port is connected to the recording and playback module. There are many such modules available on the market. This article uses the recording and playback module with ISD4004-08 as the core (as shown in Figure 4). This module has a built-in LM386 power amplifier circuit, which can record 16 segments and 480s of recording. You only need to add a 15ms to 30ms negative pulse signal to the corresponding port to play the recording, which is very convenient to operate.

Figure 4

2. Software Design

This system uses a point-to-point scanning method for each gear of the combination switch to determine whether the switch is good or bad. At the same time, it can also detect whether the internal wiring of the combination switch is correct and whether there is a short circuit between the leads. At the same time, in order to improve the test efficiency, an automatic test function is added. When the combination switch is removed, the system automatically resets. After the next combination switch to be tested is placed, the system automatically starts testing. The program flow chart is shown in Figure 5.

Figure 5 Program flow chart

3. Installation and Use

After the circuit board shown in Figure 2 is connected to the peripheral leads, the combination switch presses the probe switch, and the system automatically starts testing. At this time, the combination switch needs to be turned to each gear in turn. When the gear is normal, the corresponding indicator light is on. When all gears are qualified, the total qualified indicator light is on, and a voice alarm is sounded. The detection device has been applied to the production site, and the detection effect is very good.