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| finding short on motherboards with a shorty (with display) |
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| zoltanh:
Few pictures with the last case design, 3D printing. The schematics and PCBA are without changes versus the previous versions. PCBA is made with SMD components and as I said the schematics is inspired from Shorty but has some important changes and I am not using an additional ADC. I used 4 wires probes and there is a compensation/calibration procedure. Actually, you compensate the resistance of tip up to its solder point to wires. The probe wires are directly soldered on PCB and I opted for power supply through Arduino's USB from charger or power bank. I calculated the cost with components I bought from TME and is almost 40 euro with PCB made in house - ready made laminate with UV photoresist - by photo transfer method. Probably with components from China and large ordered quantity of pcb to a manufacturer the cost is 1/3 of this one but the lead time of 2-3 months is overkilling. I would be able to build 4-5 pieces/week with components from TME but I do not think is any interest at price of 50-60 Euro/piece. I already found out short-circuits on several multilayered PCBA in just few checks. It is a very efficient tool for locating the short-circuit, and the accuracy in comparison with the professional/industrial milliohmeters with which I checked is difficult to explain. |
| kripton2035:
with the integrated 10b adc you can have sufficient resolution to find shorts, you need to be below 1mΩ to find the short precisely. you can play with the adc amplification factor to get this right. but you loose the highest value you can measure at 400mΩ max. with the 18b adc I use, I can go from 10µΩ to around 3.5Ω that's a far better for the use of finding shorts. and by the way I added a new digit to the display, to read the 10µΩ and it is still quite stable reading ! on my prototype it's quite amazing . and the pcb are coming from china, slowly I confess. but as it is a hobby work, I'm not in a hurry. |
| zoltanh:
Your schematics is much better but also complex and based on TME prices you must add some 4-5 Euro to the cost. However, I like very much your solution and construction, and if you remember when I started to design/build my circuit you have been the first person I asked about opinion regarding shorty as at that time you built the original shorty. Also, I got inspiration of exponential tone function from you as initially I have tested several solutions which worked satisfactorily but I liked more your solution. I opted for fast conversion and oversampling and I can go up to 1.8 ohms and down to 10 microohms accurately and stable and it seems to me it is perfect for locating the short in efficient and effective and quick manner. After first three versions I gave up to five digits after comma as you gain little bit more speed and stability and make no difference in comparison with four digits in finding the short circuit. I have seen at somebody from Russia a schematics of milliohmeter just with MCP 3421 without opamp and it seems also quite ok. On other hand I believe Scullcom used also oversampling with external ADC and opamp on his milliohmeters, I do not remember exactly as at the time I have seen his work I was not interested in milliohmeter subject. Industrial made PCB are much nicer as aesthetic and easier to hand soldering as pads are tinned and isolated by soldermask. |
| kripton2035:
I left the possibility to use the internat 10b adc in my schematic, the aop output goes to the arduino and the mcp3421. if someone don't have or does not want the 18b adc he can still use the same pcb. |
| kripton2035:
I was thinking of inverting the arduino and the display, because without that the display is too high on the box. what do you think ? |
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