#290 How do Transistor Testers work (and some other insights)

if you ask me which instruments I regularly use in my lap you will hear multimeter Ocilla scope component tester and since quite some time I asked myself how is it possible to build such a versatile component tester for less than $10 after looking at the minimal parts count of such a device I'm convinced the inventor was a genius let's have a closer look great see you tubers here is the guy with the Swiss accent with a new episode and fresh ideas around sensors and microcontrollers remember if you subscribe you will always sit in the first row component tasters sometimes also called transistor testers can deal with most of our parts like resistors transistors capacitors and so on in this video we will learn how this can be done at minimal cost find out why I think the inventor was a genius we also will learn about the different fingerprints of parts like NPN or PNP transistors and maybe you also learn some tricks on how to use the pins of your Arduino or ESP s you will see why the esp8266 is 5 volt tolerant let's start with history according to an article on hackaday marcos Freck had the idea and did the first implementation of such a tester then karl-heinz cupola and others enhanced the design as well as the software in the end the Chinese started to mass-produce the devices this is why you find many different implementations all are based on the original design and software but as quite often Marcus and his friends do not get mentioned this is bad behavior of the Chinese after this video at least you know the history all models have a few things in common they have three test pings a display a button to start and a battery in addition some have a nice-looking graphical display and some a rotary encoder driving an extended menu system my first transistor tester had a small alphanumeric display and was only capable of dealing with transistors diodes resistors and some capacitors as you see I added a 3d printed case and a switch because it is only used for short moments the switch was not necessary I learned that the 9-volt battery lasts forever also without the switch it has a five-pin socket for the three test pins as well as areas on the PCB to connect SMD parts to the test pins this test was mainly replaced by this one because I wanted to be able to measure inductors the new one has a bigger display and a for keeping safe socket usually used in EEPROM programmers the last one I got has all that plus three cables to connect directly to parts if we want to test a part the first question arises immediately how do we connect the legs to the test pins and where can we input the type of the part whether it is a resistor a capacitor or something else the first question has a simple answer even if one tester has five and the others have fourteen pins all devices have three test pins the remaining pins are somehow connected to these three pins usually you'll find the numbers on the PCB close to the pins they are labeled one two and three pay attention not all devices use the same principle for example this one has a weird assignment on one side of the socket the next questions which test pin is used for what where is ground where do we have to connect parts with the two lakes and how do we have to insert components with three legs these questions are even easier to answer because the first great idea of Marcus you do not need to know that because the testers find the pinout automatically but how do they do it for that we have to dig a little into the diagram of the testers as well as the Arduino chip used in all testers let's start with the Arduino chip we all know that we can switch a pin as input or as output using the command pin mode it offers three possibilities output input and input pull-up let's now take a microscope and zoom in on how the engineers at Atmel solved the problem of creating these universal pins here is the simplified diagram of a pin of an 80 mega chip it has three resistors and three switches as well as a connection to the analog to digital converter also it has two diodes which protect the chip if you accidentally connect the pin to a negative voltage or two more than VCC here is also the secret behind the 5 volt compatibility of the esp8266 for example on the esp8266 VCC is only 3.3 volts and if you connect five volts to a pin this diode starts to conduct if you would connect your power supply to the pin a very high current would flow across this diode and it would destroy the chip in milliseconds but if you connect the output pin of a sensor to the pin the current is limited by this resistor inside the Censorship like that the diode reduces the voltage too little above VCC and the ESP is not destroyed but let's return to the component testers here we can forget about the two diodes and also the pull-up resistor because they are not needed let's assume we configure our pins as an output then the switch DD is closed and the pin is either connected via the 22 ohms resistor to VCC or via the 19 alms resistor to ground these values by the way are only approximations and can differ in reality now we can switch the level of the pin using the command digital right low or high this command moves this switch but what happens to the level of the pin if we select pin mode input then DD is opened and the pin has a high impedance it is only connected to the ADC and nearly no current can flow each pin can have three different states brand VCC and open this is why such pins are also called three state pins Marcos knew about that but he knew much more he knew that all our parts behave differently otherwise it would make no sense to have such a lot of different parts right but he had a huge problem to overcome the only thing such a pin can measure is voltage from 0 to 5 volts and because all MCS use clocks they also can measure time and now the genius begins he connected to resistors to each of the three test pins and then he connected these resistors two pins of the Arduino besides that he attached one Arduino pin directly to the test pin looks pretty simple but as with all great things it has to be simple everybody can build complicated things if we simplify the drawing and arrange it a little different we can choose of seven possibilities for each test pin ground or VCC by a 680 ohms resistor open ground or VCC via 400 70 kilo resistor ground and VCC in addition to these seven possibilities we can measure voltage now let's connect a resistor between test pin one and two if we connect pin one to VCC and pin two to ground a current flows through the resistor but I said before Arduino only can measure voltage no current so Marcos selects the 680 ohm resistor for pin 1 and creates a voltage divider now the Arduino can measure the voltage at test pin 1 and calculate the resistor we insert it between test pin 1 and to cool of course we can see limitations the accuracy of the measurement heavily depends on the accuracy of VCC of the 680 ohm resistor and the ADC in the Arduino VCC is usually not very precise but as I showed in video number 10 you can adjust for that error by using a reference voltage this is a task of the lt1000 regional design or the TL 431 in my Chinese clones then the suppliers should use precise 680 and 470 K resistors they do not do it they use standard assembly parts because of the price and the ADC of the Arduino is also only 10 bits so do not expect high accuracy but we will lay to see if this is good enough if we talk about a courtesy we have to mention the reason for the 470 K ohm resistor it is used if we insert a high resistor of for example 1 mega ohm then the voltage at test pin 1 would be very close to VCC then the software changes to the 470 K resistor and the voltage is much lower this is the next trick Marcus used to get a vast range of detectable parts with acceptable accuracy now we are done with understanding the principle let's look at the next problem Marcus faced here you have the whole mess many different parts to distinguish and test if we start with the passives he has to detect resistors capacitors and inductors then three types of diodes I know diodes usually are not called passives but the space here on the slide was handy to put them here by the way do you know how to separate a standard diode from a Schottky diode yes the Schottky diode has a much lower forward voltage of only around 0.3 volts the standard diode has one of approximately 0.7 volts this is why we often use Schottky diodes in power supplies now you see how markers worked he had to find a fingerprint for each part category and not only that but he had also to make sure that not two part types have the same fingerprint let's go to the active components if we start with transistors we have bipolar Junction transistors or bjts and field effect transistors also called fits in the BJT s we have NPN and PNP transistors then we have two categories of effects both available in N and P channel versions but that's not all we also have IGBTs thyristors and triacs i do not know how he thought that he could create a distinctive fingerprint for each category in this mess but obviously he believed it and finally he got quite good at it on top of that we never should forget this device has no clue which leg is inserted in which test pin an additional complication and one thing you should also remember some of these parts are very delicate and can be destroyed by over voltage or over current especially if you do not know which pin is which and insert them the wrong way so he has to make sure that the device never starts with a lethal voltage if it's not 100 percent sure to see the tester work let's have a look at the voltages of the three pins if we insert a resistor on pin 1 and 2 pin 1 is the yellow trace pin 2 is green and pin 3 is blue the tester tries various things and based on each measurement it selects new tests until it is clear that a resistor is between pin 1 and 2 then it measures its resistance and displays the result the resistor by the way is a 470 ohm resistor and the bench multimeter measures 465 ohms not bad if we connect the same resistor between test pin 1 and 3 the tester has to select a different test pattern but in the end the reading is the same excellent now let's try a capacitor here we have to talk a little on how we can measure capacity with this poor Arduino which is blind on nearly all eyes and only can measure voltages and time if we connect a resistor in series to a capacitor it is charged over time as you know now the tester easily can create such a diagram by connecting VCC via the 680 ohm resistor and this is what we see on the oscilloscope pin 2 stays at ground and the capacitor is charged through pin 1 the formula is like that if we wait a specific time we can switch pin 1 off and measure the voltage now we can calculate the capacity because we know all parameters of the formula cool let's see the result a little bit more than two thousand microfarads but the capacitor is marked three thousand three hundred microfarads let's test it with a multimeter a little bit more than two thousand one hundred microfarads so the capacitor is oversold and the tester is okay good to know do you understand now why I love this device as the next part I have here ABS 108 small signal MOSFET purchased on Aliexpress let's test it the device says it is an NPN transistor not effect but how can it distinguish all these transistors first how can we distinguish a PNP from an NPN transistor if you know that it is a BJT and where the pins are you can switch the base between ground and VSS of course always with the 680 ohm resistor inline and NPN transistor turns on if you connect its base to VCC and a P and P BJT switches on if you tie its base to ground also a small current flows into the base pin or out of this pin if the test sample is a FET it behaves similarly but no current should flow to or from the gate because it is isolated because I bought the BS 108 on Aliexpress I do not know the truth but have some indications that the tester might be wrong in this case the BS 108 is quite a special part and might show us the borders of the component tester so do not believe blindly to its results if we use bread-and-butter MOSFETs for the tests we see for example it detects the right pins as well as the right category it even shows a beautiful picture in addition it measures a few values and displays them too it shows for example that bt of the IRL c-44 is lower than the one of the irf 540 what does that mean and what can we learn here both are n-channel MOSFETs we often use them to switch a load its source is connected to ground and it's strain to the load gate is connected to a pin of an Arduino or an ESP BT says at which gate source voltage also called vgs the FET switches on the IRL c-44 switch is on at a lower voltage than the IRF 540 as we see the latter is not usable for 3.3 volt devices because it would never switch on if we consult the data sheets it is confirmed the IRL c-44 starts to conduct at around 2 volts and the IRF 540 at 4 volts it looks like we were lucky with our part because it switched on at 3 point 6 volts by the way both transistors would work with 5-volt logic like an Arduino you see also with transistors we not only can check to which category they belong and which pins are which we can also check if they work correctly I did not test the resistors or Triax because I currently do not have them in the lab but a lot of them need higher voltages than the 5 volts of these testers so in theory they should be able to recognize these categories but in reality it often does not work these two testers can also measure inductors which is also handy because I have no other instrument in the lab which can do that and the ones with the rotary encoder have a counter and a frequency generator on board which adds even more value to the $10.00 summarized these are incredible devices and inherit a lot of engineering skills they use modern technology at its best Thank You Marcus for starting such a marvelous project because an Arduino only can measure time and voltage this device has procedures to convert current capacity or inductance into voltage and time it has a high degree of a currency in detecting the right pin and the correct category of an electronic part the measuring results are okay especially if you only want to know which value a particular part has this is more and more important because these days it is not always easy to read the cryptic and small prints on the parts if you are interested in how accurate the testers can be you can look into the 130 pages of documentation it is worth to read it also if you are interested in how you can distinguish between components you find a link in the description all in all this is one of the best investments you can make for your lab one last thing look at this program logic you can imagine how much work went into this programming and how much time into finding fingerprints for every part I hope this video was useful or at least interesting for you if true please consider supporting the channel to secure its future existence you find the links in the description thank you bye you

Channel: Andreas Spiess

Views: 69,242

Keywords: arduino, arduino project, beginners, diy, do-it-yourself, eevblog, electronics, esp32, esp32 datasheet, esp32 project, esp32 tutorial, esp32 weather station, esp8266, esp8266 datasheet, esp8266 project, greatscott, guide, hack, hobby, how to, iot, lorawan, nodemcu, project, simple, smart home, ttgo, wemos, wifi, transistor tester, component tester, tool, lab, tester, transistor, component

Id: 4Xsg8lpP75s

Length: 21min 45sec (1305 seconds)

Published: Sun Sep 29 2019