Pocket PC Oscilloscope

S

stk2008

New Member
Hi all I am dabbling with this

https://www.virtins.com/page2.html

I am playing with the

VIRTINS Pocket Multi-Instrument.

I am using a Dell Axim X50 PDA that is receomended due to it being able to accept an external input via the headset jack.

They sell the probes (very first link I posted at the very bottom).

But I want to know if I can make one? just till I can get some moneys to purchase one.

If you look at the specs they say no more than 24v in and providing you dont go above that the output voltage will never be any more than 3v.

All the info is there for some one that knows what they are doing but I dont know what to do.

Any advice would be great.

Thanks
 
Looking at this pdf manual they seem to cover the input. Pages 30 and 31 I believe. The trick is that sound cards have a pretty wide range of input impedances. For example to make a relatively accurate 5:1 or 10:1 probe it would be nice to know the actual device input impedance. I would start using 4 diodes for clamping as they show and maybe 1 M ohm in series with each input. Using maybe an old BIC or similar pen to fabricate the probe(s) as you have 2 channels.

Ron
 
The probes are just a standard Cro probe with a RCA plug fitted to the end instead of the standard BNC connector used on Cro probes.

If you look on Ebay you will find Cro probes out of China real cheap, and will just need a standard BNC to RCA adaptor from any Hifi shop to make it work.
You might even find a BNC to stereo jack instead of using a RCA to stereo jack as they show in the photo.

I have used the Chinese probes for years now and have had no trouble what so ever.

Pete.
 
Thanks so much all this is great.

I have a probe that I use on me tek 2205 could I use this if I get a connector?.

Thanks
 
Yes, that should do. I was assuming you wanted to build one. Off the shelf should work. I assume it is a 10:1 probe?

Ron
 
Hi there yes its a 1:1 and 10:1 it has a switch I assume all so I would be best off using it ONLY in the 10:1 setting?.

Thanks
 
Yes, you want to use 10:1. Audio cards are not quite designed like scope inputs. They are also not very forgiving. Likely would not hurt to shove a few diodes in as shown in the link I posted earlier. You just don't want to damage your sound card.

Ron
 
Otay!
 
Hi all I am stumped here.

I have managed to hook me test probe to me PC line in and I am sure its sending a signal to me sound card but the problem is when I connect a 1.5v battery I dont get a decent read out just messed up crap or some times nothing.

I was expecting to get what I do on me tek 2205 and thats the trace jumps 1.5 line up but it wont it just some times goes up and with out me even releasing the connection the line comes back to ground lever on its own?.

Any one else used these free sound card based oscilloscopes?.

Thanks
 
The sound card is AC coupled, it cannot digitise a DC level.

The kick up and return to the 0v line is the same as you would see on your tek 2205 if you set the input coupling to AC.

Sound card scope? I would not bother with one.

JimB
 
Does it offer vertical coupling mode? You would want DC coupling to see a trace shift. If the trace shifts and returns it sounds like the voltage (battery) is being AC coupled.

Never mind, I see Jim covered it. I need to look at the last page before posting.

Ron
 
Last edited:

Isn't line in AC coupled?

edit------------------------
Oops, I should read all post first
 
Last edited:
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