Demo Board problem

Don French

I have a problem with my Javelin Stamp Demo Board.· I first realized I had a problem when the JIDE reported that "Possible Javelin on COM1·did not respond".·· My expertise is in software, and I am not the most experienced electronics guy around, but I figured maybe it was something with the regulator.· So, I measured the voltage between Vdd and Vss on the header just above the prototyping area.· And it looks fine at 4.95V.· I checked Vin and it also looked fine at about 8.17V.· Then, just for grins, I checked between Vdd and Vss on the 20-pin header.· Well, guess what? 0.17V!· So, now I am confused.· I am thinking that the regulator must be OK, since I am getting 4.95V over at the prototyping header.· But a few inches away at the 20-pin header, it is 0.17V.· What is between the two besides a few inches of copper·trace?· I have nothing plugged into this board except the Javelin module, the serial cable in the JDE port, and the power supply.·

The next thing I did was to run·down to Hobby Engineering and buy another Javelin module.· I plugged it in and·now I get +5V at Vdd on both headers, so I guess the original·Javelin module was·fried or·something. ·But that is not the end of it, because the JIDE doesn't recognize this one either. Any ideas on what it could be and what to do next?

Chris Savage

Don,

·· First of all, what type of computer are you using?· Is it a Laptop or Desktop?· As for the voltage measurements...The Voltage from the power supply goes into the Javelin through it's Vin pin.· That voltage is internally regulated by an on-board regulator and brought out to the Javelin's Vdd pin.· This voltage is present on the AppMod connector as well.· A lack of voltage is a good indicator that the Javelin's on-board regulator is not functioning.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Don French

I am using a desktop, but I have been using the same computer with the Demo board for weeks with no problem. I know all about what Vin is and what Vdd is, what I don't understand is how Vdd can be +5 at one header and 0 at the other. Can you explain that?

And now a brand new Javelin module cannot be seen by the JIDE, which makes me think I have a problem with the Demo board. Either that, or the brand new Javelin is no good either, which I really doubt.

Peter Verkaik

The vdd just above the prototype area (connector X3 in schematic)

is from the onboard regulator.

The vdd on the appmod header (X1) is from the Javelin.

These are seperate voltages, make sure you do not tie·them together.

See the board schematic here:

http://www.parallax.com/javelin/downloads.asp

regards peter

Don French

Really!? Two different Vdd's and they are both marked the same and you aren't supposed to tie them together? I suppose it says that somewhere in the manual and I just forgot from when I read it a couple years ago.

<Time passes while I go read the manual>

You know what? I couldn't find any such warning in the manual. I couldn't even find any description at all of the X1 header. On page 7, where it displays the Demo board and lists its features, it never even mentions X1 in the list of features. It does say that the power header is suppied by the linear voltage regulator, but someone not intimately familiar with the Javelin might not know that means "not the onboard regulator, stupid - NEVER TIE THE TWO TOGETHER"! And even if it did say that, it would also be helful if the manual mentioned that the Vdd on the X1 header was the one you were never supposed to tie to the Vdd on the other header.

So, anyway, it is clear that I fried something on the Javelin module, probably the onboard regulator, right? My next question is why doesn't my brand new Javelin module work? The regulator apparently works on this one because I have +5 at all the right places. But the module can't be found on my COM port, the same COM port that I have been using for the past few weeks with the old module on the same Demo board.

There seem to be four possibilities:

1) I fried the comptuer's COM port at the same time I fried the Javelin
2) The new Javelin is defective
3) The new Javelin behaves differently than the old Javelin when communicating through the JIDE port due to some design change between the two.
4) When I did whatever bozo thing it was that fried the first Javelin (yes, I did a bozo thing), I damaged something on the Demo board related to the JIDE port

I tested the computer's COM port by plugging an old COM mouse in and it worked, so I think the computer's COM port is OK.

I didn't have anything connected on the Demo board when I tried it the new module, so I am quite certain that I didn't accidentally fry it when I tried it, but it could have arrived defective.

I am not aware of any design changes since two years ago, but maybe I am wrong.

This leaves the Demo board. Looking at the board schematic (thank you, Peter), it looks like about the only thing that could be wrong would be C3 or C4.

Should I just blunder ahead and swap them out, or maybe someone has another idea? Thanks for listening.

Peter Verkaik

I don't think it is C3 or C4.

Your new javelin supplies +5V at the vdd pin of connector X1, so the new javelin

outputs +5V at its pin 21, so the new javelin regulator works.

If you happen to have a BS2 you can try to insert that and check if the basic stamp

is recognized. That way you can be sure the demoboard is ok.

The only other option I see with the new javelin, is to re-insert it (note pin 1) and

try to identify it again.

regards peter

Don French

I brought the new module back to the store I bought it from, and they verified that the module was defective and replaced it for me. So, I am a happy camper again. Thanks for your help.