Lapho onjiniyela be-elekthronikhi benza umklamo ohlanekezelwe noma umsebenzi wokukhanda wemishini ye-elekthronikhi, kufanele baqale baqonde ubudlelwano bokuxhumana phakathi kwezakhi kokungaziwa. ibhodi yesifunda ephrintiwe (PCB), so the connection relationship between the component pins on the PCB needs to be measured and recorded.

The easiest way is to switch the multimeter to the “short-circuit buzzer” file, use two test leads to measure the connection between the pins one by one, and then manually record the on/off status between the “pin pairs”. In order to obtain the complete set of connection relations between all “pin pairs”, the tested “pin pairs” must be organized according to the principle of combination. When the number of components and pins on the PCB is large, the number of “pin pairs” that need to be measured will be It will be huge. Obviously, if manual methods are used for this work, the workload of measurement, recording and proofreading will be very large. Moreover, the measurement accuracy is low. As we all know, when the resistive impedance between the two meter pens of a general multimeter is as high as about 20 ohms, the buzzer will still sound, which is indicated as a path.

Ukuze uthuthukise ukusebenza kahle kokulinganisa, kuyadingeka ukuzama ukubona ukulinganisa okuzenzakalelayo, ukurekhoda nokulinganiswa kwengxenye ye-“pin pair”. Kuze kube manje, umbhali uklame umtshina wendlela olawulwa yi-microcontroller njengethuluzi lokubona ekupheleni, futhi waklama isofthiwe enamandla yokuzulazula yokulinganisa ukuze kucutshungulwe ngemuva ukuze kuhlangatshezwane ukukala okuzenzakalelayo nokuqoshwa kobudlelwane bendlela phakathi kwezikhonkwane zengxenye. ku-PCB. . Lesi sihloko sixoxa kakhulu ngemibono yokuklama kanye nobuchwepheshe bokulinganisa okuzenzakalelayo ngomjikelezo wokuthola indlela.

Imfuneko yokulinganisa okuzenzakalelayo ukuxhuma izikhonkwane zengxenye engaphansi kokuhlolwa kusekethe yokuthola. Kulokhu, idivayisi yokuhlonza ifakwe amakhanda amaningi okulinganisa, aholelwa ngaphandle ngezintambo. Amakhanda okulinganisa angaxhunywa kuzinto ezihlukahlukene zokuhlola ukuze kutholwe ukuxhumana namaphinikhodi engxenye. Ikhanda lokulinganisa Inombolo yezikhonkwane inquma inani lamaphini axhunywe kumjikelezo wokutholwa kuqoqo elifanayo. Khona-ke, ngaphansi kokulawulwa kohlelo, umtshina uzohlanganisa “amapheya amaphini” ahloliwe endleleni yokulinganisa ngayinye ngokuvumelana nesimiso sokuhlanganisa. Endleleni yokulinganisa, isimo sokuvala/sokuvala phakathi “kwamapheya ephinikhodi” siboniswa njengokuthi ingabe kukhona ukumelana phakathi kwamaphini, futhi indlela yokulinganisa iyiguqulela ku-voltage, ngaleyo ndlela yahlulele ubudlelwano bokuvula/ukuvala phakathi kwawo nokuwuqopha .

In order to enable the detection circuit to select different pins in sequence from the numerous measuring heads connected to the component pins for measurement according to the principle of combination, the corresponding switch array can be set, and different switches can be opened/closed by the program to switch the component pins. Enter the measurement path to obtain the on/off relationship. Since the measured is an analog voltage quantity, an analog multiplexer should be used to form a switch array. Figure 1 shows the idea of ​​using an analog switch array to switch the tested pin.

Umgomo wokuklama wesifunda sokutholwa uboniswa kuMfanekiso 2. Amasethi amabili okushintshwa kwe-analog emabhokisini amabili I no-II emfanekisweni alungiselelwe ngamabili: I-1 ne-II-1, I-2 ne-II-2. . … ., Ⅰ-N kanye no-Ⅱ-N. Ukuthi ukushintshwa okuningi kwe-analogi kuvaliwe noma cha kulawulwa uhlelo ngomjikelezo wokukhipha amakhodi oboniswe kuMfanekiso 1. Kumaswishi amabili e-analog I no-II, iswishi eyodwa kuphela engavalwa ngesikhathi esifanayo. Isibonelo, ukuze uthole ukuthi ingabe kukhona ukuhlobana kwendlela phakathi kwekhanda lokulinganisa 1 nekhanda lokulinganisa 2, vala amaswishi I-1 kanye ne-II-2, futhi wenze umzila wokulinganisa phakathi kwephoyinti A nomhlabathi ngokusebenzisa amakhanda okulinganisa 1 kanye no-2. Uma kuyindlela, Khona-ke i-voltage endaweni A VA=0; uma ivuliwe, bese kuthi VA>0. Inani le-VA liyisisekelo sokwahlulela ukuthi bukhona yini ubudlelwano bendlela phakathi kwamakhanda okulinganisa 1 kanye no-2. Ngale ndlela, ubudlelwano bokuvula/ukuvala phakathi kwawo wonke amaphini axhunywe ekhanda lokulinganisa bungalinganiswa ngokuphazima kweso ngokuvumelana isimiso sokuhlanganisa. Njengoba le nqubo yokulinganisa yenziwa phakathi kwezikhonkwane zengxenye ecishwe uhlobo lokuhlola, umbhali ukubiza ngokuthi ukulinganisa kwe-in-clamp.

If the pin of the component cannot be clamped, it must be measured with a test lead. As shown in Figure 2, connect one test lead to an analog channel and the other to ground. At this time, the measurement can be performed as long as the control switch I-1 is closed, which is called pen-pen measurement. The circuit shown in Figure 2 can also be used to complete the measurement between all the clampable pins of the measuring head and the non-clampable pins touched by the grounding meter pen in an instant. At this time, it is necessary to control the closing of the switches of No. I in turn, and The switches of Route II are always disconnected. This measurement process can be called pen clamp measurement. The measured voltage, theoretically, it should be a circuit when VA=0, and it should be an open circuit when VA>0, and the value of VA varies with the resistance value between the two measurement channels. However, since the analog multiplexer itself has a non-negligible on-resistance RON, in this way, after the measurement path is formed, if it is a path, VA is not equal to 0, but equal to the voltage drop on RON. Since the purpose of measurement is only to know the on/off relationship, there is no need to measure the specific value of VA. For this reason, it is only necessary to use a voltage comparator to compare whether VA is greater than the voltage drop on RON. Set the threshold voltage of the voltage comparator to be equal to the voltage drop on RON. The output of the voltage comparator is the measurement result, which is a digital quantity that can be directly read by the microcontroller.

Ukunqunywa kwe-threshold voltage

Experiments have found that RON has individual differences and is also related to ambient temperature. Therefore, the threshold voltage to be loaded needs to be set separately with the closed analog switch channel. This can be achieved by programming the D/A converter.

The circuit shown in Figure 2 can be used to easily determine the threshold data, the method is to turn on the switch pairs I-1, II-1; I-2, II-2; …; I-N, II-N; form Path loop, after each pair of switches are closed, send a number to the D/A converter, and the sent number increases from small to large, and measure the output of the voltage comparator at this time. When the output of the voltage comparator changes from 1 to 0 , The data at this time corresponds to VA. In this way, the VA of each channel can be measured, that is, the voltage drop on RON when a pair of switches are closed. For high-precision analog multiplexers, the individual difference in RON is small, so half of the VA automatically measured by the system can be approximated as the corresponding data of the voltage drop on the respective RON of the pair of switches. Threshold data of the analog switch.

Dynamic setting of threshold voltage

Sebenzisa idatha ye-threshold elinganiselwe ngenhla ukuze wakhe ithebula. Lapho ukala ku-clamp, khipha idatha ehambisanayo etafuleni ngokwezinombolo zamaswishi amabili avaliwe, bese uthumela isamba sawo kusiguquli se-D/A ukuze sakhe i-threshold voltage. Ngesilinganiso sesiqeshana sepeni kanye nesilinganiso sepeni, ngenxa yokuthi indlela yokulinganisa idlula kuphela iswishi ye-analog ye-No. I, kudingeka idatha ye-switch threshold eyodwa kuphela.

Ukwengeza, ngenxa yokuthi isekethe ngokwayo (i-D/A converter, isiqhathanisi se-voltage, njll.) inamaphutha, futhi kukhona ukumelana kokuxhumana phakathi komshini wokuhlola kanye nephinikhodi ehloliwe phakathi nokulinganisa kwangempela, i-threshold voltage yangempela esetshenzisiwe kufanele ibe ngaphakathi komkhawulo. kunqunywa ngokwendlela engenhla. Engeza inani lokulungiswa ngesisekelo, ukuze ungahluleli kabi indlela njengesifunda esivulekile. Kodwa i-threshold voltage eyandayo izokweqa ukumelana okuncane kokumelana, okungukuthi, ukumelana okuncane phakathi kwezikhonkwane ezimbili kwahlulelwa njengendlela, ngakho-ke inani lokulungisa i-threshold voltage kufanele likhethwe ngokunengqondo ngokuvumelana nesimo sangempela. Ngokuhlolwa, isifunda sokuthola singanquma ngokunembile ukumelana phakathi kwamaphini amabili anenani lokumelana elingaphezu kwama-ohms angu-5, futhi ukunemba kwalo kuphakeme kakhulu kunokwe-multimeter.

Several special cases of measurement results

The influence of capacitance

When a capacitor is connected between the tested pins, it should be in an open-circuit relationship, but the measurement path charges the capacitor when the switch is closed, and the two measurement points are like a path. At this time, the measurement result read from the voltage comparator is path. For this kind of false path phenomenon caused by capacitance, the following two methods can be used to solve: appropriately increase the measurement current to shorten the charging time, so that the charging process ends before reading the measurement results; add the inspection of true and false paths to the measurement software The program segment (see section 5).

Influence of inductance

If an inductor is connected between the tested pins, it should be in an open-circuit relationship, but since the static resistance of the inductor is very small, the result measured with a multimeter is always a path. Contrary to the case of capacitance measurement, at the moment when the analog switch is closed, there is an induced electromotive force due to the inductance. In this way, the inductance can be correctly judged by using the characteristics of the fast acquisition speed of the detection circuit. But this is in contradiction with the measurement requirement of capacitance.

The influence of analog switch jitter

In the actual measurement, it is found that the analog switch has a stable process from the open state to the closed state, which is manifested as the fluctuation of the voltage VA, which makes the first few measurement results inconsistent. For this reason, it is necessary to judge the results of the path several times and wait for the measurement results to be consistent. Confirm later.

Confirmation and recording of measurement results

Considering the above various situations, in order to adapt to different tested objects, the software program block diagram shown in Figure 3 is used to confirm and record the measurement results.