The design of the computer detector for the hottes

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Design of printed circuit board computer detector (Part 1)

[Abstract] this paper introduces the design idea of printed circuit board computer detector system, including mechanical structure, system hardware design and software design, and focuses on the hardware and software design scheme

key words: printed circuit board; Detector; computer; Design

1 preface

in the electronic industry, the quality of printed circuit boards will directly affect the performance of electronic products. The production of circuit board needs to go through multiple processes, from computer typesetting, production of negative film, manufacturing of mold, product production to inspection. In the past, manual inspection was used for each process, which was easy to cause omissions and high product rejection rate. Using a computer detector instead of manual inspection will be more reliable than manual inspection due to the uncertainty of hardness between the standard surface and the back surface

there are many kinds of single-chip computers. Among the many kinds of single-chip computers, the 8031 of MCS-51 series of Intel company is used as the host chip of the electric inspection machine in this paper

2 structure and principle

2.1 general drawing of mechanical structure

as shown in Figure 1, work 1. Pointer type tensile testing machine: due to the low testing accuracy of this kind of traditional tensile testing machine, the test parts (composed of probe) are placed on the platform, and the tested board is placed on the test parts, which are positioned with the test parts through the positioning holes. Press the pressing plate downward to contact the tested circuit board with the probe, so as to measure the path or open circuit of each corresponding point on the circuit board. The up and down movement of the pressing plate is controlled by the air cylinder

2.2 principle of telescopic probe

probe structure, as shown in Figure 2

Figure 2 structure of the probe

the probe is a component that contacts the circuit board to be tested. It is a very important component in the computer detector. The signals on the circuit board to be tested by the single chip microcomputer are all through the telescopic probe, which is made of special materials with very small contact resistance, and the head is conical for automatic calibration

2.3 principle for judging open circuit and short circuit

as shown in Figure 3, the correct state of the circuit board should be: 1, 2 and 3 are connected but not connected with other points, 4, 5 and 6 are connected but not connected with other points, 7, 8, 9 and 10 are connected but not connected with other points. Short circuit is easy between 4 and 3, short circuit is easy between 6 and 7, and open circuit is easy between 1 and 2. When measuring, insert a special retractable detector head at the position of hole 1 ~ 10, the detector head is in close contact with the upper hole, and the contact resistance is almost equal to zero, so the detection starts

the material with the lowest resistivity in the schematic diagram of the circuit board in Figure 3 is silver

(1) input the high level of the probe on hole 1, read the signals on other probes, and the correctly read states 2 and 3 are high level, and the other points are low level

(2) by analogy, increase the level at points 2 ~ 10 respectively to judge the potential of other points (completed by the single chip microcomputer)

(3) when the detection signal of each point is judged to be correct by the single chip microcomputer, it indicates that the circuit board is qualified (pass is displayed on the screen)

(4) on the contrary, if the detection signal of a certain point or several points is judged as wrong by the single chip microcomputer, the fault signal will be output. According to the mark of this signal, the open circuit or short circuit can be judged at what position

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