how do you probe tiny pins?

Thread Starter

strantor

Joined Oct 3, 2010
5,971
I'm trying to hack this Laser Rangefinder to get the measured range out of it and into some other device (arduino, PC, RPi - not sure yet). The logic analyzer I'm using has these probes which are not suitable. I tried soldering tiny wires to the pins and that worked for the IC with larger leads like you can see in the picture, but when I tried to do the same on the GP22 chip (QFN package, lower right) and on the STM32 uC I just made a mess. I'm asking two questions; one about probing with logic analyzer and another about how to permanently tap the signals once I decide which ones I need.

20220517_185323.jpg

In some youtube videos I have seen a setup where there is a bridge-like structure extended over the device under test, and spring-loaded probes that can be clipped onto it and stabbed against the desired test points. What's that called?
 

djsfantasi

Joined Apr 11, 2010
8,390
I’ve seen those clamp on test points at a convention. Just don’t know who made them. But they do exist so some clever googling should be able to find them.
 

Ya’akov

Joined Jan 27, 2019
6,008
Here, I grabbed the first thing that came to hand for a test. (I wonder how many will recognize it.)

They work really well and no danger of shorting because the adjacent clip body doesn’t allow the conductive barrel parts to touch each other.

C1341B9F-10FA-4DC4-BFF6-7CA353315FA0.jpeg
 

BobaMosfet

Joined Jul 1, 2009
2,000
Big chip:

1653587538213.png
The GP22 is a TDC (Time to Digital Converter).

I would get a datasheet for the LCD, if I were the TP in order to help figure out the comms between it and the HT1621B LCD controller. I couldn't find a real datasheet on the GP22 (it might be obsolete).
 

nsaspook

Joined Aug 27, 2009
9,987
These are most certainly the dream... but at $250 for a kit.....?
It's well under my monthly budget for repair, test and measurement equipment. ;)

A drop in the bucket compared to equipment that costs millions to buy, operate and maintain with boards priced in the thousands. It's like a high quality multi-meter, you can trust they will work, every time, all the time.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,971
I came here to say almost the same thing, but mine are these. They are quite good and seem to have the same size hooks as the ones you metioned
These look handy and I'll probably end up getting some but if they work on QFN or other legless chips I don't see how.

This is pretty close to what I had in mind but spring loaded so I don't have to hold them ( might need to probe several pins at a time).

I've seen those, but forgot about them. Would you would need a different one for each IC package?

I’ve seen those clamp on test points at a convention. Just don’t know who made them. But they do exist so some clever googling should be able to find them.
"clever googling" is an oxymoron for me. I always feel just one or two brain cells away from the perfect search term that would get me what I want, and it's very frustrating.

I did find these though; the closest thing to the concept I'm after, but I'm not convinced the flexible arms are a great idea.

https://www.sparkfun.com/products/19723


Anyone have experience with these? Do they suck as bad as I think they might?
 

Thread Starter

strantor

Joined Oct 3, 2010
5,971
This is close to what I saw but it wasn't 3D printed.

I'm beginning to wonder if what I saw was a commercial product at all. Maybe a guy just had some of these and attached them to some kind of bridging structure.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,971
Big chip:
The GP22 is a TDC (Time to Digital Converter).

I would get a datasheet for the LCD, if I were the TP in order to help figure out the comms between it and the HT1621B LCD controller. I couldn't find a real datasheet on the GP22 (it might be obsolete).
I have the datasheet for GP22 and HT1621 LCD controller.
The LCD is a custom thing, no datasheet, with a lot of non-numeric symbols/icons on it.
I would like to get a signal of exactly what's on the LCD, because the rangefinder has other features like compass, level, et. al, and calculates the hypoteneuse if you're aiming up hill or down hill. With the wires I soldered on I can see the serial commands going to it and with a small bit of effort can decode what memory areas are being written, but it will be difficult to reverse engineer their meaning (which memory areas correspond to which LCD segments and therefore the displayed values). There is a Python library out there which uses OpenCV to map out the segments of an LCD while it bit-bangs the HT1621 and I'm going to try it, but as far as I can tell, it's only ever been used to map 7-segment numeric LCDs. It requires me to disconnect the CS pin from the STM32 that's currently controlling it so that the computer can control it, which I've already done, but I think I may have messed it up in the process, not sure yet.

My first attempts were aimed at the GP22 but after reading the datasheet I became less confident that it would give me the info that I want. I think it just provides a number that corresponds to time-of-flight and the STM32 is probably turning that into a range value. I could probably scale it to a range value myself in parallel with the STM32 but there's more to the calculation than just range, and it still wouldn't give me the elevation, direction, and other stuff that I'm interested in.

It would be super cool if there is a diagnostic bus on it somewhere that is just puking out strings of all the info I want but I doubt it. I want to rule it out though.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,971
I've usually been able to probe the solder blob at the edge or add a little extra solder for a blob.
View attachment 268081

You do need good magnification with a proper solder system for this.
I'm able to solder one on. Or one every other pin. But two pins next to each other proves to be beyond my skill level. I can't solder one without desoldering its neighbor.
 

Thread Starter

strantor

Joined Oct 3, 2010
5,971
I've usually been able to probe the solder blob at the edge or add a little extra solder for a blob.
View attachment 268081

You do need good magnification with a proper solder system for this.
I read what I wanted to read there.
You didn't say anything about soldering wires on.
So how do you probe the blobs? With the clips you recommended? Or Just by hand?
What about probing 4 pins at once?
 
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