DSO138 kit

On a boring day I was looking through eBay just to kill some time. I wasn't looking for anything in particular and so I was just clicking may way through the offers. As I was looking at oscilloscopes, I found a 24€ plus 5€ shipping oscilloscope kit. After looking up the specs, I thought buying it but I didn't. I already had a DSO at the time, so I just wanted to have this kit to see what it's capable of doing and a scope to put into the backpack would also be nice.

Time passed and I forgot about it, until a friend of mine showed me exactly the same scope kit on Aliexpress for 16$ and free shipping! For it was clear the the price for something like that couldn't get lower so I just bought it.
I finished putting it together an testing it one the day it arrived. After it, I was very happy to go to bed. The next day some more tests were done, feeding different signals with different settings into the DSO138 and my other DSO to see if the measurements of the DSO138 are correct. Turns out they aren't really precise, but for a 16$ DSO certainly ok. The claimed bandwidth of 200khz is a hoax. It's about 100khz. I expected that the claimed specs wouldn't be real, but the interface is nice. I like it. One button to scroll through the settings,  plus minus buttons and a ok button, which has a hold function. Holding the select button down, when it is on the time base setting, allows you to activate measurements. You switch them on an of the same way. You also got a reset button. It's possible to save wave forms too.
The "manual" and the soldering guide are also nice. Printed in color they guide you through the soldering process and the powering up of the scope. As I heard apparently not all kits come with the manual and the guide. In case you don't have them, you can get them one the manufacturer website or the sellers page. But watch out how you solder in the switching transistors of the voltage inverter. I forgot to check and soldered in Q1, the PNP transistor in the wrong way. It did work with 9V because you are able to use a transistor in inverse mode. With emitter and collector connected to the wrong pad on the board. Then I tried 12V, which is possible according to the manual, the PNP transistor blew up and L2 too. What happend is that the PNP transistor worked somehow like a zener diode. This effect is used in white noise generators. In this case there was no resistor limiting the current and therefore destroying Q1 and the inductor that then shorted the power supply. So check with the datasheet of the transistor if you soldered correctly! As a replacement you can use a BC556/7/8 for the PNP and BC546/7/8 for the NPN if it happens to you too.

A zero alignment plus a test function is also explained.


The scope comes with a BNC to crocodile clamps cable. When you buy this scope I recommend to get a proper scope probe, Switchable or not doesn't matter here. The scope has a 1khz 3.3V test signal.

 

If you want to, you can use this scope a a development kit. It has a USB mini B connector and functionality on pin headers.

 

PS: The price of the scope that I linked might vary. 

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