• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Logic Analyzer Idea

Status
Not open for further replies.

AtomSoft

Well-Known Member
DISCLAIMER: (lol) Ok this is just me bored and tired and thinking so please dont mind if this is over simplified or sounds dumb in any way.

I love the PicKit 2 Logic Analyzer so much it gave me a idea on how to recreate it and test up to 8 inputs at a time for the same given time.

The Pickit 2 will be refered to from now on as the pickit ok lol

The pickit gives you few options on what to collect and when/length.

How about we take any PIC with a free FULL PORT like a PORTC or B with 8 full pins free... and we use those pins to gather data but only on a HIGH OR LOW situation depending on user selection.

So basically the user selects a time frame um....100 kHz (every 10 us.... then a start on HIGH situation on pin2.. we give them the option of 1-1024 (10us 10.2 ms ) samples to take.

Once they select those options and press start we wait for a high condition on selected pin2 and when high we start by taking the value of PORTC and placing it in a variable then exactly every 10us be sample the PORTC again and add to the end of the variable and so on untill the time is up.

Now with collected data we can have 2 images. a high line like a --- and a low line like a ___ then when we connect the variables to the line we essentially create a image. Im sure i can make a prototype in about a few hours but i gotta clean the house unless the wife will nag so ....

what cha think? or is it too simple lol
 

Sceadwian

Banned
No, good idea, very useful if you intend on snooping around other digital circuits. The only problem you'll run into is getting the data off the PIC and onto a PC fast enough, or storing it somehow, you could use a line based LCD to display the results but it wouldn't be very detailed.
 

AtomSoft

Well-Known Member
lol i would just store the data on the pic itself in a variable or large code space. About 512-1024 bytes long. Maybe EEPROM. Fast is simple i can use a 20MIP pic even if have to use dsPIC and then store the data in eeprom as regular full bytes and when done send them to PC and then have the PC create the images of it all this way the pic is just getting data and when done with that job sending data. Simple.
 

AtomSoft

Well-Known Member
I never said it was a LIVE feedback type thing. Its like the pickit 2 type work. It collects the info and then sends it to PC. As long as it know what info and stuff then no issue.
 

Sceadwian

Banned
Just keep in mind, at the one example you've given of a 10usec sampling period 1024 bytes of memory will only allow a 10ms capture window. You have to figure out what kind of signals you'll want to be looking at to determine if this is sufficient. Personally I've always been a very big fan of large capture buffers, I'd rather have too much data than not enough. This however could be solved easily with external memory.
 
Last edited:

Sceadwian

Banned
For a simple logic analyzer a DSPic is overkill. The advanced functions are simply not needed. Personally I'd use an AVR, or a PIC with a PLL clock multiplier, preferably one that has external ram capability, SRAM modules are not that expensive. Then capture buffer size isn't so much of a problem.
 

DirtyLude

Well-Known Member
Hardware for a simple logic analyzer is easy and plenty of hobbyists have made them.

To me a logic analyzer is the software more than the hardware. Just seeing little up and down lines is not very useful to me. Protocol analysis, is what a analyzer is best at. Easy viewing of pulse widths and times on the screen. Saving and retrieving logs for comparison...

You can look at Joe's blog when he was creating the Saleae logic analyzer. It has some interesting things in there, and it's an interesting example of getting something to market.
Joe 2008 Web Edition - Vox
 

AtomSoft

Well-Known Member
heh it is a overkill but somewhat like you said i rather have a overkill then a underkill lol meaning i rather have tons of options on a pic and not use then have one with no options and be in need of external parts.

This had 4KB vs the 1KB on a normal pic. If i use external memory most of the memory out there has around a 5ms write time and how would i capture 10uS data if it takes 5mS to write it lol

even 1mS is too long. I rather be able to write to eeprom anyway. Everything on chip. Thats a nice idea tho. You are a smart fella. You have any good thoughts on memory (EXTERNAL) that i might have a look at? Some links?

Thanks again for your interest in this. I know i might try to sound right or say something dumb but please i will never mean to offend anyone in anyway... im a harmless punk :D

So any more ideas?
 

Sceadwian

Banned
That's one of the things I like LTSpice for =) As long as you can format the data you can load stuff like that as a Piecewise linear voltage source, and then feed that into any virtual circuit you care to build.
 

Sceadwian

Banned
Atom, it's simply, go with a cheaper pic that has the ability to use external memory. Then you can buy big SRAM chips. You'll get MUCH more memory for the same price as a DSPic
 

AtomSoft

Well-Known Member
Thanks i completely understand what you are saying its just that most external memory takes too long to write to. By the time i write to it i would have missed a bunch of captures.
 

Sceadwian

Banned
External ram should be far faster to write to than eeprom.
 

Sceadwian

Banned
5mS?! You seem to be highly disillusioned about the speed of external SRAM. You're only limited to the timing of the SRAM chip in use. A few us maybe not ms.
 

DirtyLude

Well-Known Member
The Saleae Logic is nice, but I just meant to show that the hardware isn't very remarkable. The solution it has is to dump the logic data to the USB as fast as possible. It turns out that 26Mhz data is pretty much the limit for this.
 

AtomSoft

Well-Known Member
Sceadwian i would like to see those chips that go that fast. Can someone post me a link please. I do believe you and would actually love to see some info on them.
 

Sceadwian

Banned
It's called SRAM =)
Check digikey, access time is between 15ns and 150ns
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top