Microcontroller pinout determinant of bipolar transistors. Scheme, description

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Microcontroller pinout determinant of bipolar transistors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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In the magazine "Radio" No. 8 for 2005 on p. 30, 31, a description of a similar device was published - "Microcontroller determiner of transistor outputs" (author V. Krasnov). This device has some disadvantages - the relative complexity of the circuit and the inconvenience of using, since to determine the pinout of the transistor, you have to use a special table, and not a direct indication. Therefore, a device was developed that is free from these shortcomings, the scheme of which is shown in Fig. 1. It is much simpler and is equipped with a direct indication of the outputs of the transistor under test and its structure.

Microcontroller pinout determinant of bipolar transistors
Fig. 1

The basis of the device is the DD1 microcontroller, it is configured to work with an RC generator, the frequency of which is set by the R1C2 circuit. In a certain sequence, set by the program, pulses with an amplitude close to the supply voltage are formed on the port lines RB2, RB4, RB6. Through the integrating circuits R2C5, R3C4 and R4C3, the transistor under test is connected to these lines. Voltages from capacitors C3, C4, C5 are supplied to the port lines RB7, RB5, RB3, where they are measured.

Information about the pinout and structure of the transistor is output from the RAO-RA3, RB0, RB1 port lines using the HL1-HL8 LEDs, which are located on the board in accordance with the contacts of the XS1 socket. LEDs HL2-HL4 (red glow) indicate the output of the base, HL6-HL8 (blue) indicate the output of the emitter, and LEDs HL1 and HL5 indicate the structure of the transistor. The principle of dynamic indication is used to control the LEDs.

Microcontroller pinout determinant of bipolar transistors
Fig. 2

The principle of operation of the device is illustrated in Fig. 2, and voltage oscillograms are shown in fig. 3. First, a check is made under the assumption that the output of the base is connected to the input (Fig. 2). The base of the transistor receives a voltage smoothly increasing from zero (Uout2 from the integrating circuit R2C1 (Fig. 2). Due to this, the collector current appears with a delay and the voltage across it (Uout1) also decreases smoothly.

The threshold voltage (Fig. 3) of a low level (Uthreshold will be reached after the time interval At, which is measured by the microcontroller. Next, the transistor is tested in another combination of outputs, where the assumed emitter and collector are interchanged, and the previous procedures are repeated. The microcontroller compares the measured time intervals At in the first and second cases.

Microcontroller pinout determinant of bipolar transistors
Fig. 3

Because the inverted transistor has a lower static base current transfer ratio, the rate of change of the collector voltage will be slower and delta t will be larger, which is used to determine the collector output. After successfully determining the pinout, the program turns on the appropriate LEDs to indicate the pins and structure of the transistor, and then jumps to the beginning and the whole cycle repeats. The duration of the test and indication cycle is a few milliseconds, so the LEDs seem to be on all the time.

If, during the measurement process, the threshold voltage is not reached within a certain specified time interval - about 1 ms, it can be concluded that the position of the transistor base in the tested pin configuration is incorrect and the program proceeds to checking another configuration. There are three such configurations for transistors of different structures. After unsuccessfully checking all six options, a decision is made that the transistor is faulty or it is not connected to the device. In this case, the device switches to the on state indication, while one of the LEDs (HL1) flashes and the entire transistor test cycle is repeated.

All elements are mounted on a board made of fiberglass foiled on one side, the drawing of which is shown in Fig. 4. MLT resistors with a power of 0,125 or 0,25 W were used, capacitor C2 - K10-17, the rest - for surface mounting, size 1206. The microcontroller is installed in the panel. All high-brightness LEDs with a housing diameter of 5 mm, HL1-HL4 are red, and HL5-HL8 are blue. But it should be noted that with a supply voltage of 3,6 V, the brightness of the blue LEDs may not be sufficient. In this case, you can use green LEDs or increase the voltage. Switch SA1 - any small-sized. The simulation of the device operation was carried out in the Proteus Release 7.5 SP3 program.

The appearance of the mounted board is shown in fig. 5, and the entire device - in Fig. 6. Instead of wire jumpers between capacitors C3-C5 and terminals 9, 11 and 13 of the microcontroller, resistors with a resistance of not more than 10 Ohms are installed. To increase the reliability of pinout detection, it is desirable to increase the clock frequency. To do this, the capacitor C2 can be excluded, the microcontroller generator will operate on the parasitic capacitance of the microcircuit and mounting, and its frequency will be about 3 MHz. Tests with three copies of chips showed reliable operation of the device in this mode.

The supply voltage can be in the range of 3,6 ... 6 V, so the device can be powered from a stabilized charger (5 V), a cell phone battery or a battery of three or four AA, AAA galvanic cells. In standby mode, the current consumption is about 2,5 mA, in the mode of measurement and indication of outputs - 8 mA.

To check the device, testing of transistors of various series was carried out: 801, P803, MP805-MP807, MP809, MP 812, MP819-MP903. In all cases, the pinout of serviceable transistors was determined correctly.

The program for the microcontroller can be downloaded from ftp://ftp.radio.ru/pub/2011/11/tester.zip.

Author: V. Stanaitis

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