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

[badboydas]

Anyone building Shorty should note that all MCP3421's are not equal, the SMD code dictates the address (which you would change in the code line 45)
If SMD code is
CAxx = 0x68
CBxx = 0x69
CCxx = 0x6A
CDxx = 0x6B
CExx = 0x6C
CFxx = 0x6D
CGxx = 0x6E
CHxx = 0x6F
some of you will have known this,some may not have

I have still have not got it fully working but it is now talking to the MCP3421 @ address 0x69

[clearchris]

If there's a question of addresses, there are sketches included in the arduino gui where you can flash a program to the arduino and scan the i2c or spi bus for addresses.

[badboydas]

Originally Posted by clearchris

If there's a question of addresses, there are sketches included in the arduino gui where you can flash a program to the arduino and scan the i2c or spi bus for addresses.

Yes you are right, but the code states
"0x68 is the default address for all MCP342x devices"
Not every one here would be a keen programmer.

[badboydas]

And the line underneath,yeah come on this is hard work
uint8_t address = 0x69; // addresses do vary depending on smd code

[clearchris]

Originally Posted by badboydas

Yes you are right, but the code states
"0x68 is the default address for all MCP342x devices"
Not every one here would be a keen programmer.

I have done some i2c work lately, and if I can't communicate with the chip, the first thing I do is scan for addresses, not to really check for the address, but to verify communication and wiring.

Hopefully I'd have noticed the different address, but I can't say for certain I would have.

[Erico1]

I am a member of the forum where the design work is being discussed for the shorty with display.

There is some recent activity on this project ( as of June 2022) in the thread.

The OP in the EEVlog forum mentioned possible selling the Gerber file for the PCB and I am definitely on board with that.

[stj]

gerbers arent the issue,
i could cad that up in an hour or so.

the issue is Kripton changed the circuit because it couldnt provide enough stable current.
and a full circuit with changes wasnt released.

[clearchris]

That doesn't sound insurmountable. Couldn't we slap a linear regulator on there and get the current required?

[stj]

can you get linear regulaters operating at sub-volt range?
these testers use very low voltage to avoid turning semiconductors on.

[clearchris]

From the other thread, here's megaraider's 2c.

"The current source problem arises from using the 5V output line from the Arduino Nano.
As he wrote somewhere he couldn't figure out why the voltage (5V) dropped when the tips were connected. The LM1117IMPX-5.0 max. load current is 800mA.
While that might seem to be enough it's not: one must take in account the Arduino ICs, display, DAC, Op Amp and tips current source overall power consumption!
Therefore, replace that 5V line with a reliable 5V power supply."

5v regulators are very common, I'm pretty sure I have multiple types on hand even.

If that doesn't work, there is a schematic here for a series regulator, doesn't look that terrible. https://en.wikipedia.org/wiki/Linear_regulator

It's entirely believable that these nano clones use underpowered regulators. I would really be surprised if you were able to run them at 100% of spec.

[Per Hansson]

It can apparently also have a uA78M05 regulator and that is only good for 500mA:
https://www.arduino.cc/en/uploads/Ma...0Schematic.pdf

[stj]

so we need a 78s05?

[clearchris]

Originally Posted by Per Hansson

It can apparently also have a uA78M05 regulator and that is only good for 500mA:
https://www.arduino.cc/en/uploads/Ma...0Schematic.pdf

And sub in some chinese regulator to make BOM for a 3 usd board, there's your voltage sag. Can't say I'm surprised. I almost never use the on board power to run peripherals.

We could easily use a 78s05 as stj suggested (in jest?). We probably need to change the nano power to use the 5v pin instead of the vin pin. It would probably be better to have everything use the same power source.

[Per Hansson]

Well, you could use a regulator with a little bit better dropout voltage than 3000mV if you're going to power it from a battery I say!
I was looking for a replacement to my ESR tester and came across this 1117 with 350mV dropout and rated 1.2A it is a pretty nice upgrade over a standard 1117 at least:
ST LDL1117S50R: https://www.mouser.se/ProductDetail/...FiVf%2Fg%3D%3D

[clearchris]

Sounds good to me, what do you think stj?

[stj]

hard to believe that package can give 1.2A
i wonder how much copper groundplane it wants.

[stj]

looking closer,
maybe we should run it at 3.3v
then we can use a lithium cell instead of a 9v battery that may only be good for a few hundred mA
maybe a 500mA cell from a disposable vape together with a usb charger/protection pcb

either way, the BC557 has to go.
a P-type mosfet would be better

[redwire]

A one or two transistor constant-current source is not difficult, and possible to voltage-limit it. On laptops, GPU etc. I could see a need to keep it under 2V max.

[megaraider]

Originally Posted by clearchris

From the other thread, here's megaraider's 2c.
"The current source problem arises from using the 5V output line from the Arduino Nano. (...)
Therefore, replace that 5V line with a reliable 5V power supply."

Originally Posted by clearchris

5v regulators are very common, I'm pretty sure I have multiple types on hand even. (...)
It's entirely believable that these nano clones use underpowered regulators. I would really be surprised if you were able to run them at 100% of spec.

[And above posts...]

My thoughts FWIW:
a)
Is portability so important (at least at this stage)?
We all know it will be sitting on our workbench... will it not!
For what's worth we can even power it from an rescued ATX power supply.

b)
It's much better to have everything connected to the same power source.
Bypass / tweak Arduino board to use it instead (that shitty regulator is for costs saving only).

c)
YES, the LDL1117 will be able to deliver over 1A output current just like an 'old' LM7805 is.
As always it comes down to the heat sink: it's never to small!
Moreover, want to boost output current to several amps? The 'old' 2N3055 will boost it... Again the heat sink comes into play!

d)
Yes that BC557 has to be replaced! It's farmost and basic for current source.

[stj]

so lets use a chinese buck convertor
i think they can go down to 1.8v at 3A