Products > Test Equipment
MS05000 Budget Logic Analyzer Probe Set Design
skip:
It works! I discovered this thread last Tueday and today I have my very own working probe set. I ordered the boards from Ted on Tuesday and they arrived on Thursday, I ordered the parts from Digikey on Wednesday and they arrived on Friday! Wow, what amazing service.
So far I've built 2 X 3.3v versions, I think I'll take a break and build 5 volt version if and when I actually need them.
I must say the assembly was a WORKOUT for me, I mostly do software work and although I've been soldering for over 50 years stuff this tiny was a real challenge!
Thank god for my Metcal (ebay) soldering iron and my Amscope microscope or it would have been hopeless. I was too paranoid to try drag soldering so I soldered each pin individually with my .25mm tip. I'll might try drag soldering on the next board, the resistors and caps took most of the time anyway.
All thee boards worked perfectly the first time.
The picture shows my completed probe wired to a surplus Pano Logic thin client which I've programmed with an 8 bit counter clocked by 125 Mhz to generate test signals. As you can see the scope measured and displayed the fastest signal of 62.5 Mhz without problem.
Thanks for the project Ted!
notfaded1:
Can't beat Metcal after I bought a 5k with dual irons... I'll never go back.
Gandalf_Sr:
Nice job Skip, glad they are working for you.
electricMN:
I finally got some boards built and tested. The only problem I found building them was locating a 1.4mm key wrench to fit the potentiometer. I ended up getting a couple from McMaster-Carr, I was ordering some other stuff from them anyway.
I tested it by hooking it up to an Arduino Uno board which had a digital caliper hooked to it reading the serial data from the caliper. I ran into a problem with hooking the Arduino I/O pins to the LA. The Arduino has built in pull-up resistors on the inputs that are 20K. The LA has 10K pull-down resistors on its inputs. I had to add 2K pull up resistors on the I/O pins on the Arduino in order to get it to work with the LA. I think I'm going to replace the pull-down resistors on the LA with much larger values. I think they're there just so there are no floating inputs on unused inputs.
Thanks for the hard work putting this project together Ted. :-+
Gandalf_Sr:
electricMN
Thanks for posting the pictures and the comment about the pull down resistors. I discuss these resistors earlier in the thread; I found it works fine without them but the datasheet for the voltage level translator IC says the input pins shouldn't be left floating - I'm sure that 100k or even 1 Meg would work just fine.
The Piher trim pot was chosen because it's sealed and rated for 1,000 operations (unlike many trimmers that are only rated for 100). If you check the datasheet, you'll see that it's supposed to be available in Phillips head type too but the only type Digikey ever seems to have in stock is the Hex drive.
Anyway, glad that you got it working OK and the pictures look great!
:)
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