Intro: DIY Oscilloscope Kit - Assembling and Troubleshooting Guide
I need very often, when designing some electronic gadget an oscilloscope to observe the presence and form of the electrical signals. Until now I have used an old Soviet (year 1988) single channel analogue CRT oscilloscope. It is still functional and normally is enough good for the purposes used, but is very heavy and not comfortable for some works outside home. For its replacement I was looking for a cheap and tiny alternative. One possibility was to design an Arduino based scope, but it has few disadvantages - its analog bandwidth is quite low and always, when making some DIY project appears the main problem - where to pack all these electronic parts or how to find nice looking housing. I do not own 3D printer and for me the only possibility is to use standard cases available on the market, what not always is the best looking solution. To avoid these troubles I decided to get a DIY Oscilloscope kit. After some research I decided that it would be the JYETech DSO150 Shell. It is very small, enough powerful (based on the ARM Cortex 32-bit microcontroller STM32F103C8 - very useful site for this chip: stm32duino), I can put in my pocket and carry it everywhere. The kit can be purchased for ~ 30 USD in banggood, ebay or aliexpress .
This instructable tells how to assemble the kit in the right way, what you should not do and how to get clean from the troubles, you could create. I will describe all my assembling experience in the chronological way.
Step 1: What Is Inside.
I ordered the kit and after the normal waiting of around a month the kit arrived finally. It was nice packed. It contained two PCB's with all SMD devices soldered. (When you order such kit be careful - there is a version of the kit in which the SMD devices are not soldered, and if you do not have experience in the soldering of such devices - it could be heavy challenge for you - better order a kit with soldered ones). The quality of the PCB's is good - all devices labeled and easy to solder. One of the PCB's is the main one - the digital one with the microcontroller. There we have also connected a color 2.4" TFT LCD ; the other one is the analog - it contains the analog input circuity. There is also a nice plastic box, short probe cable and assembling guide.
My advice - before starting the assembling - read the manual. I did not do it and I went in troubles.
Step 2: Let's Start...
As first step is recommended to test the digital board. I have inserted the 4 switches without soldering. I have found a 12V AC/DC adapter with the proper DC socket and used it to test the board. Very big mistake! DO NOT DO IT! In the manual is written that the maximum supply voltage should be 9V! I saw that the linear regulator used was AMS1117, which must survive 15V and I was calm. OK. At the first test it did not fail. See the movie.
Step 3: Soldering...
As first I have soldered the test signal connector. It must be first bent. Follow the battery connector and the power switch. After that comes a 4 pin header (J2) for the rotary encoder. With that the soldering of the main board has finished.
Step 4: I Am in Trouble!
There is a 0 Ohm resistor on the PCB, which bridges the power switch. To make the power switch functional this resistor (R30) must be removed. Easy done! New test... I have supplied the main board again (12V) and switched it on using the power switch. The screen remained white. (see the video). Few consequent attempts did not change the situation. Suddenly a tiny smoke started to go out of the AMS1117 regulator chip and it package blew up. I unsoldered it and placed a new one (I had few in my personal storage available). I powered up again the board - again white screen - no booting. After 20 seconds again came the blue smoke from the regulator chip and it burned out again. I removed it from the board. Using ohmmeter I have measured the resistance between the power line connected to the output of the AMS1117 chip and the ground. It was zero Ohm. Something went absolutely wrong here. The board was dead. I decided to find out where the problem is. There are two chips on the board - the STM32F103C8 and some serial memory chip. One of them was failing. To check which I used unusual method. I applied 3.3V (what should be the normal output of the AMS1117 regulator chip) on the supply line using strong power source. After few seconds the STM32F103C8 chip became extremely hot. It was the problem. It had to be unsoldered from the PCB It was very difficult task because I could not use hot air gun - it would desolder all surrounding devices. Then to me came the idea to desolder the chip by its own heat - I supplied the board again and after a minute the chip was so hot that the solder started to melt down. After that I removed it with a small kick on the bottom side of the board. The chip simply felt down. Using desoldering wick I cleaned up the soldering tracks for the chip.
I decided to try to repair the board. After removing the failing chip the LCD screen was again illuminated white.
I have ordered few STM32F103C8 chips form aliexpress. (4 chips were~ 3 USD) and after few weeks waiting they have arrived. I have soldered one of them on the board.
Now - it has to be programmed to recover the functionality. If all tasks are done correctly - everything should be OK again.There is also possibility that the LCD screen could be damaged. For that there is also a solution available - you could buy such one in aliexpress. It is standard 2.4" 37 pin colour TFT LCD using ILI9341 controller. Check also the pins order.
How to program the STM32F103C8 chip is described in the next step.
Step 5: Programming
The process of the programming the ARM chip is written in the attached document.
Under this link you can download the last flashing tool from the STM site.
Yo can see my setup on the picture. I have attached also the hex file, which I used. For the last version, you can visit the site of JYETech. For the USB to serial communication I have used PL2303 based converter. FT323RL also will work. CH340g as well. Before programming of the board some resistors must be desoldered from the board. (see the document). Do not forget to solder them again when everything is ready. I had luck and everything went good again. I continued with soldering of the analog board.
Step 6: Again Soldering
First must be soldered the resistors. I have used an Ohmmeter to check their value instead using color code.. At each soldered part I put a mark on the manual to know where I am.
After that I soldered the ceramic capacitors, the trimming capacitors, the functions switch, the electrolyte capacitors, the BNC connector, the pin header.
Step 7: The Rotary Encoder
It must be soldered on a small board. Be very careful to solder it on the proper side of the PCB - in other case the scope will fail.
Step 8: Assembling
Now we are ready for assembling.
First place the LCD in the dedicated place. I have removed the protecting folio before that. Under the scope I have put few layers soft kitchen paper. Bend gently the LCD connection flat cable and put the main board over it. Insert the rotary encoder in the header connector and fix it using two of the short screws
Step 9: Tuning
Now the analog board must be inserted as shown on the picture. In this way some analog voltages must be checked by voltmeter. Be aware that some of them depend on the supply voltage ( I have found this). The voltages written in the table at step 4 of the manual are measured at supply voltage 9.2V. After that some distortions of the signal (see the picture above) can be corrected by tuning of the trimming capacitors. See the procedure in the manual... and attached movie.
Step 10: Assembling and Final Tests
Now the analog board is fixed at the bottom cover.Both boards are joined together by their common pin-header interface. At fist the test terminal must be inserted. The top cover frame is put. Be aware that if you not orient it correctly, you will not be able to close the box.(see the picture above for the correct orientation). The housing is closed and after that fixed by 4 screws. As final step the plastic knob must be put over the rotary encoder shaft.
Now the scope is ready to use. It has internal test signal generator and this signal can be used for some adjustments and learning. The functionality of the different knobs is described in the manual. The short video shows some of the functions. One of them shows a lot a signal parameters in real time, what can be very useful in some cases.
Thank you for the attention and good luck with playing. Have a fun with this small toy - toy for adults and young electronics freaks,