[ edit ] Basics
Every hobbyist knows well the problem: one is building a transistor from a single device, or extracting one from the junk box. If the designation is to recognize (and one is known), is all in order. Often, but not the way, and then the usual times is happening again: pick out the type and pinout of the transistor from the Internet or a book. It's annoying in the long run, of course, pretty. Also transistors in the same case are not always the same pin configuration. For example, a 2N5551 has a different occupation than a BC547, although both have a TO92 package. If there is no longer visible in a transistor, the name (or not even Google what to do), it is with conventional methods really complicated to figure out the types of transistors: It could be NPN, PNP, N-or P-channel MOSFET, etc. act. Eventually, the component also has a protection diode internally, the identification is made even more difficult. By trial and error by hand is a quite time-consuming task.
Why should this not be done by a microcontroller? This automatic transistor tester is developed.
[ edit ] Features
Even Chief FETs (JFETs for example) are now supported. In power thyristors and Traics can lead to problems if the test current (7 mA) below the holding current content. MOSFETs and transistors were detected but in my tests always accurate.
[ edit ] Hardware
It is advisable to open the schematic in another browser window to understand the following descriptions can.
When the microcontroller ATMega8 was chosen. He has more than enough flash and RAM. He also has enough port pins and is very inexpensive. The transistor tester is operated with a 9V battery. The 5V operating voltage for the AVR is generated quite conventionally with a 78L05. At the port B of the ATMega8 different resistances are connected: the transistor pin a large (470 k) and a small (680 ohm). This allows two different currents on the pin to be tested are given. The resistors are connected to ADC0, ADC1 and ADC2. These pins and the transistor to be tested is connected. The left part of the circuit (with the 3 transistors) is responsible for the automatic shutdown. More on that later. On the first pins of port D, the LCD is connected. This is a 2x16 character text LCD with HD44780 compatible controller.
It should be noted that the test inputs have no protection. A suppressor would probably distort the results. It should therefore not components that are installed into a circuit to be tested. Otherwise the ATMega8 damage.
[ edit ] Test Procedure
The test of the transistor based on a simple but effective principle:
There are first time tried out all six possible combinations for the
Pin1 on +, to Pin2 -, pin 3 free
For each possible combination is checked whether there is between the + pin and the pin passage. For this is determined by the ADC, the voltage at the + pin. If continuity exists, and the falling voltage in the range between 0.2 V and 4 V, is to be expected from a diode between the relevant pins. This result is stored. The test is thus not of course be canceled, as this may be achieved even with a transistor and is (a transistor has two pn junctions, which is 2 diodes).
If no continuity exists, previously left open pin over 680 ohms to ground. If now continuity, there must be a PNP transistor or p-channel MOSFET. In this case, the pin (it is then the base) placed over the 470 k resistor to ground. Now the tension between the + and Pin-pin (collector and emitter) are measured and stored.
If however there is still no continuity between the positive and
negative pin, the pin first, released more than 680 ohms is set to
increase. Is now run, there is a npn transistor, an n-channel MOSFET or a thyristor / triac. The remaining steps are at the PNP. The first pin is left open but then again switched to high impedance. If the component will still be forwarded, it is a thyristor or triac.
To measure the gate threshold voltage of N-channel enhancement MOSFET source is placed firmly on ground. Drain is a 680-ohm resistor set to positive and gate is placed over a 470kOhm resistance to positive. The tester then waits until the MOSFET switches, so the drain goes to logic 0. Now the gate voltage is measured. This is about the gate threshold voltage.
For the measurement of resistance is made up of one of the internal
resistors (680 ohms or 470kOhm) and the test, a voltage divider. The voltage at the midpoint of the divider is measured, once with the 680Ohm and once with the 470kOhm resistance. From this, the resistance of the specimen calculated.
For a 6-ohm test on the other hand, it is 0.044 V in the middle of the divider, at 8 ohms, it is 0.058 V. Here, the resistance also increases by 33%. The voltage divider in the middle but only increases by 0.014 V, which increases the ADC value by only 2 to 3.
By the way, each measured specimen resistance is both the 470kOhm resistance and with the 680Ohm resistance. In the analysis, then the more accurate result is used, meaning earnings in which the divider voltage is closer to the optimum value of 2.5 volts.
The total measurement range is about 5 ohms to 910kOhm. In the range below 20 ohms, the measurement is very inaccurate, departures of 10-20% can occur already.
The measurement of capacitors is separated from the measurement of the remaining components. This means that it has an independent measurement function, which checks in all 6-pin combinations on the presence of a capacitor. This is necessary because the measurements would disturb each other.
The presence of a capacitor is tested as follows: One of the two pins
is placed firmly on ground and the other over 470kOhm to ground.
The result is then displayed on the LCD. Then the tester will automatically turn off after about 10 seconds.
[ Edit ] view on the LCD
The calculated test result is displayed on the LCD. In the first row next to the recognized type of component is displayed. The following components are identified so far:
Depending on the component you will see some data:
Since most JFET drain and source are equivalent, these connections can not be detected. It may happen that the drain and source are shown reversed in JFETs.
A distinction between bipolar and polarized capacitors capacitors was originally planned.
[ edit ] Automatic shutdown
The simplest course would be to put the AVR after completing the test too easy in the power-down mode and easy via push button again to wake up the next Test. The AVR needs in this mode, less than 0.3 uA. As the battery would last almost forever. Since the tester but needs stable 5 V, to get a voltage regulator is a must. Here is already the problem: The voltage regulator is still cheerfully, even if the unit is asleep, and consumes little power while not so: A 78L05 takes about 3 mA. That would make the battery in just one week empty. Even the thrifty LP2950 requires only 75 uA. As the battery would last only nine months. Better, but far from ideal.
But there is a better option: the current of a pnp transistor in the positive line (T3) position. Hereby, the standby current is just ~ 10 nA (0.01 uA mA or 0.00001). A 9 V battery with 500 mAh would thus theoretically empty after 5,000 years. That should probably ...
Description of this circuit:
The resistors R11 and R12 are used for measuring the battery voltage. At low battery voltage, a corresponding message ("battery") is displayed on the LCD.
In the thread to the article was repeatedly expressed the desire to build the transistor tester without the automatic shut-off. Instead, then a simple switch is used. This saves a lot of components. The software must not be changed for it. Switch S1 is optional if automatic shutdown is not installed .. In order to run a new test cycle without the tester for this and turn out to have again. Those who do not need can simply omit it. Attention: The switch is of course only optional if the tester is constructed without the automatic switch-off!
[ edit ] Information regarding the software
In the archive available for download a ready-compiled firmware version for the ATmega8 and a smaller one for the ATmega48, and the complete source code is included. The version for the ATmega48 has not the following features:
These features of the ATmega48 has not enough room.
To change between the version for the ATmega8 and ATmega48 switch, just in the project options in the Makefile or the AVR types accordingly: For "Selbstkompilierer. About # ifdef blocks are then automatically (from the square) is activated only on the ATMega8 possible features on or off.
It is strongly recommended that you set up the tester to the ATmega48: This controller is not much cheaper than the ATMega8, and the firmware for this is hardly cared for even more, because it is (understandably) in any case hardly used, in addition, the controller provides for Program improvements no room left.
I think it would be nice if it found errors in the software or suggestions in the forum thread writes to the article.
[ edit ] Troubleshooting
If anything is showing on the display, the following things to check:
on a 2x16 display case only one line are shown as blocks in the second row and nothing, then when connected using an adapter cable to connect completely twisted (Pin 1 Pin 16 on the board so the LCD screen). There may be also an error in the initialization screen (different from HD44780). But these are only 2 other possible ways forward.
If components are correctly identified with a specific order of the connections to the test pins, component is detected although it did not connected or data such as the gain at different connection sequences diverge significantly, should the board for solder bridges, bad solder joints or similar . be reviewed. Between the test pins should remain no residual flux. Flux is usually slightly conductive. Since the used test currents are very low, can also lead to the current flowing through the flux to a distortion of the result.
[ edit ] Links
[ edit ] Downloads
Note: The development now takes place in an SVN repository. There are also extras (such as board layout). Who wants to be sure to get an upgrade, you should either check out the archives or download the snapshot that is more than a day old.