finding short on motherboards with a shorty (with display)

[cybermaus]

Not sure I see the difference with your earlier rendering?
And both of these renderings are the same?

But while indeed I think the display is rather "north" and not very centered, I do not think it is very important either way.
As long as it works.

Also, if you want the display a little more centred on the box,you could place the 9V battery on the other side.

[nikifena]

Nice project! Thanks for sharing.
Just a few ideas. What about adding an input protection circuit - two back-to-back 5V Zener diodes or unidirectional TVS?
In order to reduce the HF noise what about a 100pF capacitor across R7 and R8 and for better HF DC filtering 100nF across C3.

And more. Using off-the-shelf battery chargers with a USB port it could be done with a li-ion battery. Here is a good example: https://www.aliexpress.com/item/1005001466320793.html

[nikifena]

Hi everyone again.
I was thinking about how to improve the project, so here are my ideas:

1. Switching to tactile switches for powering and all other functions. Using 12mm tactile switches with caps has a few benefits - they sit well next to the display and the height is good to fit everything into a box. Also, having an electronic power on, there could be integrated auto power off. Two switches can be used for four different things:
SW1 short press - on/off
SW1 long-press - mute
SW2 short press - relative mode
SW2 long-press - calibration

Auto power off after some time 30-60seconds when the tester is not used.

2. Adding a lithium battery with a built-in charger and battery protection - usually, there are cheap PCBs from Aliexpress and they could be used here in order to make the project simpler. I realized that there is not necessary to have a 5V boost circuit. The voltage from a single battery can be used directly to power the Arduino and the display board. Only the current source left, so I suggest using a precision reference voltage with an enable pin. I found LT4120 as a good solution. There is a version with 2.5V output. Just an extra transistor will increase the current capabilities. A precision voltage source will improve the stability and the readings too.

3. Adding relative mode. There are two ideas:
-A classic relative mode - Just connect the probes to the circuit and press the relative mode to zero the reading or
-First select relative mode, then connect the leads to the circuit. When the value reading is stable, a beep indicates that the relative mode is used. In this mode, when a low value is measured, two fast beeps could indicate that for faster short finding.


4. Increasing the range of the unit. This could be done for the next revision of the unit. Switching some resistors could do that. There could be two more ranges - micro ohm range and ohm range (up to 100 ohms for example) The ranges could be automatically selected.


I've been working as a PCB designer for the last few years, so I'm happy to do a good-looking PCB. I can't modify the code, so I will be happy if kripton2035 will agree to improve the whole project.

I will put a schematics idea soon.

[kripton2035]

Everybody is free to do what they want with this project, that's why I published it.
so you can have a li-ion charger if you want. I prefer a simple 9v liion battery because I have plenty of them.
I HATE auto power off systems because they NEVER really switch off. and when you need the device that sat in a drawers for some time, the battery is flat
this never happens with a good old mechanical switch.
I'm already thinking at REL mode and greater range, but as you said it will be for the next release.

[kripton2035]

anyway your idea of moving the din plug and the arduino to the bottom to have room for the display and button is very nice. adopted !

[nikifena]

Dear kripton2035, the auto power-off circuit is not leaky and won't suck the battery. Both MOSFETs are off when the circuit is off and there is no leaky path.

For the current path resistors, I choose 2512 footprint for R2 and 1206 for the 1R resistors. The bigger resistors have higher thermal mass to keep the resistor temperature more stable over time keeping the readings accurate. I added some diode protection for protecting the frontend circuit.

The ADC is pretty good and it has a build-in PGA (programmable gain amplifier) of up to 8x gain which could be used for increasing the range of measured resistance. In this case what about reducing slightly the gain of the differential amp to 10?


Any recommendations are welcome

Niki

[sam_sam_sam]

nikifena

Can you please show the other end of DIN 5 connector

 and

I am not understanding the USB connector wiring what USB charger are you connecting to this device

 ( have done a lot USB charger devices [ and battery bank packs ] and have never seen one wired this way )
( most of the time the two center pins [ are shorted together or there is a resistor network ] on a USB charger are for sensing the charging current for the device that is plugged in so this where I am confused about what you have done here )

Are U2 U4 and U5 are suppose to be connected together  because I am a little confused here as well

Please do not take what I have pointed out here the wrong way I am just trying to understand what you have here to understand how it is wired together and be able to troubleshoot this device if should ever have to

Thanks

[Kean]

I am not understanding the USB connector wiring what USB charger are you connecting to this device

 ( have done a lot USB charger devices [ and battery bank packs ] and have never seen one wired this way )
( most of the time the two center pins [ are shorted together or there is a resistor network ] on a USB charger are for sensing the charging current for the device that is plugged in so this where I am confused about what you have done here )

For charging nikifena mentioned above about using an off-the-shelf "cheap PCBs from Aliexpress" so I assume the USB Charger component is meant to be one of those.

Are U2 U4 and U5 are suppose to be connected together  because I am a little confused here as well

Yes, they all share the I2C bus using the labelled SDA and SCL nets.  Oh, he called it "SLC "...

One thing I don't like in the posted schematic is the 2x1k constant load on the battery even when powered off.  It would be better the place that divider on Vcc and only sample it when Q1 is enabled, or even better duplicate the Q1/Q2 high side switch circuit off another GPIO to only supply the divider while reading the battery ADC value (less than 1ms).

[kripton2035]

prototype pcb ordered.
last pcb view is below.

[Maximilian]

Some time ago I built the same project from the same HackADay article with a Liion battery and it's really nice to have.
It's very handy to have to quickly find shorted capacitors and it has saved me quite some time.

The only problem with it is that the battery discharges quite quickly, I hope this can be solved.

Looking forward to building the upgraded EEV version.
 

[nikifena]

Dear Kean, thanks for the notes! You are absolutely right, the battery level calculator 1k divider resistors must be connected after the soft power switch. This divider could be made by 27k resistors since they exist in the current BOM. And yes, the I2C pin must be SCL. kripton2035, the clock and data pins on the Arduino are reversed on your schematics.

And more.
What about removing the current precision opamp gain stage and using only an ADC with built-in PGA with a variable higher gain. There are a couple of up to x128 gain ADC's with 24-bit resolution. The marked in blue  MAX11270 and CS1237 are my favorites for now. What is necessary: fast readings with more digits

Anyone with programming skills to write/modify the code?

kripton2035, your design looks better now.

sam_sam_sam, There are cheap PCBs from China with a USB-C connector, a battery charger IC and battery under and over-voltage protection too. Here is a quick example: https://www.aliexpress.com/item/1005001581000751.html
The DIN5 connector has a kelvin wiring to the probes as shown.

Niki

[kripton2035]

The only problem with it is that the battery discharges quite quickly, I hope this can be solved.
Looking forward to building the upgraded EEV version.
 

I never recharged the 9v battery I use for the prototype since the beginning of this project. hours if not days of use really.
yes. it is a mechanical switch, I prefer them to any "auto off" methods that never really off the power for that main reason.

[Mechatrommer]

[de_light]

What about removing the current precision opamp gain stage and using only an ADC with built-in PGA with a variable higher gain. There are a couple of up to x128 gain ADC's with 24-bit resolution. The marked in blue  MAX11270 and CS1237 are my favorites for now. What is necessary: fast readings with more digits
Niki

I like the idea of your suggestions! Any chance you can release the schematics/gerber files on a Github or something so others can collaborate?

[kripton2035]

I've implemented 6 digits to my shorty prototype. 10µΩ resolution. with 16 bits and pgax8.
but it's not stable. only the 5th digit is ok. this is not a precision instrument. not sure if 24 bits will add a lot of usability.
you may have to change a lot of other parts of the design to achieve it.

[cybermaus]

You have my support @kripton2035. Stay the course, lets get a few 5 digit ones in actual use before we start over complicating based on paper specs.

[masterx81]

Any news about this?
Had to repair a notebook with a ceramic mlcc cap shorted at 1.6ohm and i really tought that with shorty it would have taken much less time to spot it instead of constantly watching the display of the milliohm meter That sort of work that you do not too often but when you have to check dozens of caps on a mainboard  can be really annoying. 

[kripton2035]

I've received the pcb's.
had to deal with a voltage regulator mcp1755s not working at all when in parallel with the arduino regulator. this took quite some time to figure out.
rebuild the code to have a simple calibration procedure: you measure 0 ohm and 1 ohm and the calibration is done.
now I only have some instabilities that are not on the prototype ( ! ) that makes the measure instable at "high" ohms
you can measure in theory up to 7 ohms
I also changed the constant current (that was not one) with a zener.
we are almost there. will make a demo movie soon.

[masterx81]

Good job!
Quite interesting that on the prototype with flying wires on proto board all was stable, and with a proper pcb with good ground plane not 
In the mantime i need to source an accurate 1 ohm reference 
Most of the shorted things that i've found were under the 7 ohm (only few in the 30ohm range), so must be a good value.

[kripton2035]

these : https://www.aliexpress.com/item/1005002205975393.html
seems fine and enough for the purpose of this tool.

I would like the tool to be able to measure up to 1-300Ω to handle any kind of situation
but it would require a more capable adc.

[DavidAlfa]

This is very interesting. I looked at these DIY options last year, but hadn't time for that.
I have 4 digit decimal resolution DMMs at work (ex. 0.2145Ohms) which are great at tracing shorts, although very slow (1 reading/sec or even less when set in max precision)
However these are $$$$ expensive, I was searching something for myself, for hobby use.
I bough a $2 DT830G DMM to play with, aiming to modify it by adding an op-amp, so the 200 or 2Kohm scale become mOhms.
I'll update if I get enough accuracy out of it! It'll probably be crap but who knows

[AndrewBCN]

Great project, and the Arduino code is very well written, really an example of how to write clear, easy to maintain code. Thank you for sharing!

[kripton2035]

I have a pending update for the code, where I auto-measure the probes values at short and 1Ω value to auto calibrate the device...
will be there ... soon. stay tuned.

[jaromir]

Hello guys, I'm the author of the original project on hackaday.io
It was quick one evening work before contest deadline, serving as backup project in case the main one would have a problem. More of a toy than proper tool.
I must admit I'm delighted to see somebody found it useful and stunned by how far you brought the development, turning my quick and dirty hack into useful gear. Great job!

[cybermaus]

So. Is anyone already selling kits? Or ordered a bunch of PCB and have 2 to spare?