I already wrote about choosing budget soldering station in one of my previous posts. I might find some time to write a post on how you can tweak it in order to get a better performance. However this time, I would like to share some experience about another important tool for tinkerers or DIY’ers – transistor tester with AVR microcontroller.
In the reality, this tool does a lot more. I have no clue why it was called only the transistor tester even if it detects automatically different electronic components; measures the Equivalent Series Resistance (ESR) of the capacitors, shows pinouts and type of the transistors, diodes and etc. 😉
Measuring ESR is one of the most important features for me. I considered to get a separate ESR tester already for a while but once I saw this AVR-based tester, I decided to go for it. When you do some audio or electronics DIY project (fixing, upgrading or building some electronic circuits) you might survive with the multi-meter, the oscilloscope and the soldering iron. But when it comes to deciding about the capacitor shape and quality, measuring ESR is really a must.
M328 tester design, SW&HW
I got mine tester from eBay something like a half year ago, as eBay is flooded with them. Most of them come only as soldered PCB boards while smaller part of these transistor testers are sold with the enclosures. I went for second option. When you browse eBay, you might get the impression that all of these devices were designed and produced in China. However, the reality is not exactly such. Most likely all of them are produced there, but simplistic and at the time quite sophisticated design was done by German guy Karl-Heinz Kuebbeler. You can read about this project itself here.
The device is powered by ATmega 328P (at least in my case), but the software is also compatible with other Atmega AVRs. The electrical circuit can be found here.
As you can see, it is really simple, consisting mainly of AVR with few resistors, capacitors and LCD screen 🙂 But in the reality, all complexity lies within the firmware. If you want you can compile the firmware yourself. But in this case, you will have to get empty Atmega 328P and program it yourself.
Returning back about the functionalities of this device
Everything works automatically on this device. I mean that you have three pins outgoing from the device. I would recommend to solder the extension cables with the crocodile type connectors. That will make your life a lot easier (e.g. to connect to bigger size MOSFETs or other parts). These three output pins are used for connecting to tested electronic part (resistor, capacitor, inductor, MOS or PNP transistor etc.). After doing that, you have just to press the “Test” button and you will get a result in few seconds. The device detects itself what kind of the part is connected and it shows the parameters. In some cases, that might be a limitation, e.g. you want to measure few parameters like the capacitance and the inductance. But in general, it works really well. Once I got this tester, I spent probably an hour testing different parts which I had at home 🙂 I have to admit that this device is a bit power hungry. The voltage of the battery dropped quite significantly after playing with it. But once I started to use normally, it stabilized and no any significant voltage drops occurred.
The device is also equipped with self-testing mode. If no parts are connected, after pressing “Test” earlier mentioned test is performed, at the end of which the message “No, unknown or damaged” is shown. It is possible to perform the calibration of the tester. In order to do this, you have to shorter all “1” “2” “3” pins of the tester.
It’s difficult to imagine more simplistic interface 😉 Also, the battery voltage is shown all the time when you just switch that tester. So, you will know if it is too low.