New tool to find short capacitors on motherboards : shorty with display

[gabiz_ro]

Originally Posted by kripton2035

I received the pcb some times ago. but there is a failure I did not find until now.
I made some changes in the schematic, using a constant current source for better repetability,
well I'm still investing. the voltage regulator is giving 2.4V instead of 5V
... and it does not seems to be a short circuit !

Some more info about?
I mean about voltage regulator.

[stj]

do you mean your not getting enough current from the one on the arduino?
that doesnt surprise me really.
you probably need to use a 1A linear regulator and some tantalum caps

[kripton2035]

I added a voltage regulator 1755S to bypass the one inside the arduino. just thinking there would be a better regulation than the 1117. I also added a constant current source with the pnp transistor, to have better accuracy and better reproductibility of the measures.
now I'm debugging this new schematic, it's almost working, but as a reminder it is a hobby project, and I have been very busy these last months.

[gabiz_ro]

I was more about

I'm still investing. the voltage regulator is giving 2.4V instead of 5V

As I see 1755S is limited to 300mA
Aprox 60mA via Q1 and resistors, 240mA for Arduino, oled and others.

[kripton2035]

I checked on a lab power supply, the whole device is now using 50-60mA.
the current constant source now is using 30mA.

[gabiz_ro]

Some schematic will help a lot.
Where did you get 2.4V instead of 5V with voltage regulator?
Also
Voltage drop C-E on BC557 at 100 mA is in datasheet 0.65V
5V -Vdrop on BC557 = 4.35V
4.35V on 82 + 2 +1 ohms is around 0.051A that is 51mA but since it may be pulsing lab power supply will show some intermediate value.

I'm not so familiar with Arduino but in source code seems like you defined TRANSISTOR and BUTTON both to pin 3

[kripton2035]

I'm not so familiar with Arduino but in source code seems like you defined TRANSISTOR and BUTTON both to pin 3

transistor is on an analog pin 3 A3, and button on a digital pin 3 D3
they are not the same pin.
anyway, the transistor is always on, and has been removed from the source code when I use the constant current source.

[kripton2035]

this is the actual state of the schematic of the shorty-with-display input stage.

[gabiz_ro]

Are both 3 but must be something to differentiate.
For digital pin you can define simple with number only but for analog inputs you need to specify is analog one by using A prefix.

[dicky96]

Hi Kripton
Do you have any up to date news regarding the PCB?

[clearchris]

Originally Posted by dicky96

Do you have any up to date news regarding the PCB?

He has been busy with work. I have considered building one from the schematic, but it's not enough of a priority for me to drag out the perf board.

I am getting the LCD on order though.

[stj]

it's an OLED - get a selection of white, blue and mixed colour.
i wish they sold them in green - it would look like an old crt

[clearchris]

Originally Posted by stj

it's an OLED - get a selection of white, blue and mixed colour.
i wish they sold them in green - it would look like an old crt

I have this one in my cart. Not sure I want to go back to the old days with a choice of monochrome green or monochrome amber. I don't miss that at all.

https://www.aliexpress.com/item/3280...c00gcT6Vz&mp=1

[aneng]

@Kripton2035

Hi Kripton.... it's August now !! Please say you have more information on the PCB supply - or anything about this project. I can't wait to build one !

[clearchris]

Originally Posted by aneng

@Kripton2035

Hi Kripton.... it's August now !! Please say you have more information on the PCB supply - or anything about this project. I can't wait to build one !

My LCD for this project just arrived today, it's much smaller than I thought it would be. This project should be able to fit on some perfboard. If you want to build it on some perfboard, I'll go along. Last I heard there was one last issue, and kripton was busy at work. I'm sure he will come back when he's through.

Want to work through the last issue?

[h0baz]

nice job..

[paulyboy]

Any progress?

[stj]

not here - maybe check the thread at eevblog?

[clearchris]

From eevblog:

"sending good with a value from france to outside of europe (even into europe) has become a pain in the a** since january 2021 and new EU VAT rules.
it will be easier for me, and cheaper for everyone, to sell a gerber file of the pcb, and people ordering 5 pcb from jlcpcb or like.
instead of me collecting many pcb's and sending them one by one to the world."

I could contact him and get some sent to me and send them out to others (US only) if there are enough people interested.

[megaraider]

Yes the new EU VAT rules (January 1 or Jun 1, 2021) are a really f*cking pain in the a**.
No more exclusion on small values (less than 20€, including shipment).
In practice, this means that even end consumers and non-profit receivers / senders in the EU must handle themselves all bureaucracy and collect/deliver all VAT values to EU member State, plus a fixed fee to local/end carrier.
What a f*cking mess!