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M328晶体管测试仪 测试二极管,三极管,MOSFET 等等
5.5 Selftest function 66 5.5.1 Some Results of the Selftest Function 6 Known errors and unsolved problems 7 Special Software Parts 8 To Do List and new ideas 75 Preface Basically motive Every hobbyist knows the following problem: You disassemle a Transistor out of a printed board on you get one out of a collection box. If you find out the identification number and you already have a data sheet or you can get the documents about this part, every thing is well. But if you don't find any documents, you have no idea, what kind of part this can be. With conventional approach of measurenent it is difficult and time-consuming to find out the type of the part and parameters. It could be a npn. pnp. n- or p-channel-mosfet etc. It was the idea of markus f. to hand over the work to a AVr microcontroller As my work has started My work with the software of the Transistor Tester of Markus F. I has started, because I had prob lems with my programmer. I had bought a printed board and components, but I could not program the eeprom of the aTmega8 with the Windows driver without error messages. Therefore I took the software of Markus F. and changed all the accesses from the eEprom memory to flash memory accesses. By analysing the software in order to save memory at other places of program, I had the idea, to change the result of the ReadADC function from ADC units to millivolt(mV) units. The mV resolution is needed for any output of voltage values. If readadC returns directly the mv resolution, I can save the conversion for each output value. This mV resolution can be get. if you first accumulate the results of 22 ADC readings. The sum must be multiplied with two and divided by nine. Then we have a maximum value of 1023.222=5001, which matches perfect to the wanted mV resolution of measured voltage values. So I additionally had the hope, that the enhancement of ADC resolution by oversampling could help to improve the voltage reading of the ADC, as described in AVR121 5. The original version ReadADC has accumulated the result of 20 ADC measurements and divides afterwards by 20, so the result is equal to original ADC resolution. by this way never a enhancement of ADC resolution can take place. So I had to do little work to change the readadC but this forced analysing the whole program and change of all if-statements " in the program, where voltage values are queried. But this was only the beginning of my work More and more ideas to make measurement faster and more accurate has been implemented Additionally the range of resistor and capacity measurements are extended. The output format for LCD-Display was changed so symbols are taken for diodes, resistors and capacitors instead of text For further details take a look to the actual feature list chapter 1 Planned work and new ideas are accumulated in the To Do List in chapter 8 By the way, now I can program the EEprom of the ATmega with Linux operating system without errors At this place I would like to thank the originator and software author Markus Frejek, who has enabled the continuation with his initial work. In addition i would like to say thanks to the authors of numerous input to the discussion forum, which have assist me, to find new tasks, weak points and errors. Next i would like to thank markus reschke, who give me the permission to pu blish his cheerful software versions at the svn server. Furthermore some ideas and software part of markus R. was integrated in my own software version, again thank you very much. I have to than k also asco B, who has developed a new printed board, to enable the reproductions for other hobbyists. Another thank i would like to send to Dirk w., who has handled the omnibus order for t his printed board Never i had time anough to handle these things concurrently with my software developement, at, no time the state of further developement of software would have the same level. Thanks for the many suggestions to improve the tester to the members of the local chapter of the " Deutscher amateur Radio club (darrin Lennestadt 3 Chapter 1 features Operates with ATmega&, ATmega168 or ATmega328 microcontrollers 2. Displaying the results to a 2x16 character LCD-Display 3. One key operation with automatic power shutdown 4. Battery operation is possible since shutdown current is only about 20nA 5. Low cost, version is feasible without crystal and auto power off. With software version 1.05k the sleep modus of the Atmega 168 or ATmega32% is used to reduce current if no measurement Is requireo 6. Automatic detection of nPn and PNP bipolar transistors, N- and P-Channel MOSFETs JFETs, diodes, double diodes, Thyristors and Triacs 7. Automatic detection of pin layout of the detected part 8. Measuring of current amplification factor and Base-Emitter threshold voltage of bipolar tran sisters 9. Darlington transistors can be identified by the threshold voltage and high current amplification factor 10. Detection of the protection diode of bipolar transistors and mosfet 11. Measuring of the Gate threshold voltage and gate capacity value of MOSFETs 12. Up to two Resistors are measured and shown with symbols and values with up to four decimal digits in the right dimension. All symbols are surrounded by the probe numbers of the Tester(1-3. So Potentiometer can also be measured. If the Potentiometer is adjusted to one of its ends, the Tester cannot differ the middle pin and the end pin 13. Resolution of resistor measurement is now up to 0.01, values up to 50Mn are detected 14. One capacitor can be detected and measured. It is shown with symbol F and value with up to four decimal digits in the right dimension. The value can be from 25pF( 8MHz clock, 50p F @1MHz clock)to 100mF. The resolution can be up to 1 pF(@MHz clock 15. For capacitors with a capacity value above 0. 18uf the Equivalent Serial Resistance(Esr)is is only avaiable for ATmega with at least 16K flash memory(ATmega168 or ATmega3s, re measured with a resolution of 0.010 and shown with two significant decimal digits. This feat 16. For capacitors with a capacity value above 5000p F the voltage loss after a load pulse can be determined. The voltage loss give a hint for the quality factor of the capacitor 17. Up to two diodes are shown with symbol -+H or symbol + in correct order. Additionally the flux voltages are shown 18. LED is detected as diode, the flux voltage is much higher than normal. Two-in-one LEDs are also detected as two diodes 19. Zener-Diodes can be detected, if reverse break down Voltage is below 4.5V. These are shown as two diodes, you can identify this part only by the voltages. The outer probe numbers, which surround the diode symbols, are identical in this case. You can identify the real anode of the diode only by the one with break down (threshold) voltage nearby 700mv! 20. If more than 3 diode type parts are detected, the number of founded diodes is shown additionally to the fail message. This can only happen, if Diodes are attached to all three probes and at least one is a Z-Diode. In this case you should only connect two probes and start measurement again, one after the other. 21. Measurement of the capacity value of a single diode in reverse direction. Bipolar Transistors can also be analysed, if you connect the Base and only one of Collector or Emitter 22. Only one measurement is needed to find out the connections of a bridge rectifier 23. Capacitors with value below 25pF are usually not detectet, but can be measured together with a parallel diode or a parallel capacitor with at least 25pF. In this case you must subtract the capacity value of the parallel connected part 24. For resistors below 2100Q also the measurement of inductance will be done, if vour ATmega has at least 16K flash memory. The range will be from about 0. 01mh to more than 20H but the accuracy is not good. The measurement result is only shown with a single component connected 25. Testing time is about two seconds, only capacity or inductance measurement can cause longer period. 26. Software can be configured to enable series of measurements before power will be shut down 27. Build in selftest function with optional 50Hz Frequency generator to check the accuracy of clock frequency and wait calls(ATmega168 and ATmega328 only) 28. Selectable facility to calibrate the internal port resistance of port output and the zero offset of capacity measurement with the selftest(ATmega168 and ATmega328 only). A external capacitor with a value between 100r F anld 20FF connected to pin 1 and pin 3 is necessary to compensate the offset voltage of the analog comparator. This can reduce neasurement errors of capacitors of up to 40HF. With the saIne capacitor a correction voltage to the internal reference voltage is found to adjust the gain for ADC measuring with the internal reference Thyristors and Triacs can only be detected, if the test current is above the holding current. Some Thyristors and Triacs need as higher gate trigger current, than this Tester can deliver. The available testing current is only about 6A! notice that all features can only be used with microcontroller with more program memory such as ATmegal68 Attention: Allways be shure to discharge capacitors before connecting them to the Tester! The Tester may be danaged before you have switched it on. There is only a little protection at the aTmega ports Extra causion is required if you try to test components mounted in a circuit. In either case the equipment should be disconnected from power source and you should be shure, that no residual voltage remains in the equipment 6 Chapter 2 Hardware 2. 1 Circuit of the transistor tester The circuit of the TransistorTester in figure 2. lis based on the circuit of Markus F. released in Abb.1 of AVR-Transistortester report 1. Changed or moved parts are marked with green color, optional parts are marked with red color Some changes are made because the electronical power switch make problems in some implemen tations. Therefore the resistor R 7 is reduced to 3.3kS. The capacitor C2 is reduced to 10nF and R8 is moved so that the PD6 output does not try to switch the C2 capacitor directly. Additional blocking capacitors are added and should be placed near the power connection of the atmega and near the voltage regulator Because the PD7 input and PC6(RESEt) are the only pins, where pull up resistors where needed, one extra 27k 2 resistor is added to the PD7(pin 13 input. With this modification the software can disable all internal pull up resistors of the Atmega The additional crystal with its 22pF capacitors are optional added. The accuracy of a crystal has the benefit of more stable time measurement for getting the capacitor values New software version can use a voltage scale switch of the ADC. The speed of switching is reduced by the external capacitor Cl at the AreF (21) pin of the AT mega. To avoid slowing down the measurenent speed more than necessary, the value of this capacitor should be reduced to 1IF Removing of the capacitor Cl is also possible. For adapting the software to the actual circuit take a look to the Makefile options in the configuring chapter) Some different versions of Rll/R12 resistor cornbinations circulates in the internet. I have adapted ny software to the original of Markus F. I with 10k 2 anld 3.3 k 2 The additional 2.5V precision voltage reference connected at pin PCA(ADC4)can be used to check and calibrate the vCC voltage, but is not required. You can use a LM4040-AlZ25(0. 1%),a LT1004CZ-2.5(0.8%)or a LM336-Z25(0. 8%)as voltage reference. A optional ISP connector has been added to easier load iiew software versions to the tester 7 Tm88082] a PCG(RESET) PCI(AD 100n PC3(ADC3) T1001 PC4Al)C4/SI)A Cll PB6OXTA.LI/TOSCI) PBI(OCIA MHZ C12 PBT(XTAL/TOSC2 PE4rMISOK BC557C FD5(SCK Ubar PDICTXD) VEE T DoiNT IC2 IN OU PDJ(T D)ai GND C6IOUn BC547 PDTIAINI Butto RESET OND Figure 2.1: New circuit of Transistor Tester The software can follow to another pin assignment of port D for a simpler connection of the LCD display. The following table 2. I]shows the modified assignments 1g1 circuit diagram strip grid board version pushbutton input PDZ PDO LCD-RS PD4 PD7 LCD-E PDE PD5 LCD-D4 PDO PD4 LCD-D5 PDI PD3 LCD-D6 PD2 PD2 LCD-D7 PD3 PDI Table 2.1 Changes for strip grid board For better protection of the ATmega inputs the additional circuit 2.2 can be integrated. The de-energized contacts of the relay protect the aTmega without power. The contacts will be opened by software only for measurement. BC547 七 wuiIdiry uf relay lype PC4(ADC4/5DA COIADCO TP PCI(ADCD) TP2 PC2(ADC2 - TP3 Figure 2.2: Additional protection of the ATmega inputs If the serial output of text is not required, the Pin PC3 of the aTmega can be used as analog input for measuring a external voltage. The voltage can be up to 50V with the optional 10: 1 resistor divider and can be used for neasuring the breakdown voltage of a zener diode. A current limiting power supply with up to 50V can be switched on with low signal at PD7 pinl of the ATmega to deliver current for testing the break down voltage of a zener diode. Figure 2. 3 shows a suggestion for this expansion. The tester shows the external voltage as long as you hold the key pressed. about 40mA more battery current is used by this expansion during key pressing Extermal Voltage ICom DC-DC Cont IRFUCO24 Your-15 serial/ PC3 TMACSISD Can be placed on Tester board! Should be placed separa Figure 2.3: Expansion for measuring of break down voltage of Zener diodes 2.2 Hints for building the TransistorTester Every LCD-display with at least 2x16 character and a HD44780 compatible controller can be used with the TransistorTester. You should respect the current needed for illumination, some LCD need lower current than others. I had tried Oled type displays, but this type cause interference with measurenents of the ATmega and are not recommended. Also loading of special characters for displaying the resistor symbol has caused problems with the Oled The resistors rl to ro are critical for neasurements and this 680Q2 and 470ke2 resistors should be measurement type resistors(tolerance of 0.1%)to get the full accuracy. You should use a precision socket for the aTmega microcontroller to enable the replacement of the microcontroller. The micro- controller ATmega&, ATinega168 and ATmega328 can be used. Recommended is a ATmega168 or ATmega328, if you wish to use all features Anyway you should assemble all parts to printed board without the microcontroller. A up-to-date ow voltage drop regulator like MCP1702-5002 is recommended as IC2, because it need only 2pA of standby current and can still deliver 5V, if your input voltage is only 5 4V. But this part is not pin compatible to well known 78L05 with TO92 body! After checking, that all needed parts are at the correct place, you should first connect the battery or power supply to the printed board without LCD-display and microcontroller. You should check the voltage at the power pins of the microcontroller and LCD-display terminal during the Test key is pressed. The voltage should disappear, if you release the Test key. If the voltage had correct polarity and value, you should disconnect the power and assemble the microcontroller with correct alignment Be careful and make shure, that all pins of the microcontroller are in the socket holes. Now you can also connect the LCD. Check if power pins of the LCD has the right connection to GNd and Vcc of your board If you are shure that everything is all right, reconnect the power. If you have already programmed the atmega, you can press the Test button By pressing the Test key, the background light of the LCD should switch on. If you release the Test button, the LED should illuminate weak. Notice, that the software for the microcontroller must be compiled for the correct processor type. A progran for the atmegas does not run on a ATmega168 2. 3 Changeover for tester versions designed by Markus F Voltage control If the problem exist, the tester will shut down immediately with every switch on With imy suggested setting of the fuses(Makefile) the voltage control of the different ATmega

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