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Steve Joblin
01-20-2006, 09:52 PM
Following on from what Matt Battle had started (reference http://forums.parallax.com/showthread.php?p=564291 (http://forums.parallax.com/showthread.php?p=564291)), I am looking to make own "Stamp Lite" that just has the pre-programmed PIC, EEPROM, Resonator and two resistors.

It would seem that the schematic from Weethet has a few mistakes (see http://www.weethet.nl/english/basicstamp2_homebrew.php (http://www.weethet.nl/english/basicstamp2_homebrew.php)). I tried to combine the documentation from Parallax and the comments from Matt's discussion thread above hoping that i could get it to work. Unfortunately, to no avail... here is what I have...

The first circuit is the "Programmer" that I built on a small circuit board.

The second circuit is the "Stamp Lite" that is wired on a breadboard.
http://forums.parallax.com/attachment.php?attachmentid=40145
I didn't have 1uF electolytic caps, so I used polarized tantalums instead.

I know I need to check, recheck, and check my solder joints and physical implementation, but any ideas? Basically, I am looking for a "sanity check" that if I wired everthing as show, it "should" work. Thoughts?

Chris Savage
01-20-2006, 10:11 PM
Steve,

According to your drawing here you have the Vss and Vdd lines backward coming off the bottom of the board. Not sure what you're connecting them to, but that could cause power problems. Also, you have RX and TX coming off the bottom of the board, but where do they go? The MCLR line, is it being pulled up? It look like it is going through a switch, in which case it's floating. That's what I see so far.

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Chris Savage
01-20-2006, 10:15 PM
Two more things...pin 8 on the interpreter should be pulled high via 10K or it may rest low causing a break condition, which would prevent the Stamp from running code. Also, you have a line exiting bottom called /MCLK which is actually /MCLR. /MCLK would be considered the line going between pin 6 of the EEPROM and pin 7 of the interpreter. This weekend I may post my own schematic for an OEM BS2 which is simplified. Except my design allows you to still program it using an FTDI USB chip.

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Steve Joblin
01-21-2006, 02:08 AM
Chris - thanks so much for your help! I hope I didn't fry anything by having Vss and Vdd reversed!

The "Programmer" is on the first page... the bottom plugs into my serial port on my computer... the top plugs into the header pins that are on the bottom of page 2.

I will also look into the pull-up on Pin8 of the inerpreter.

I think that /mclk was probably just a typo that I copied over from the weethet page.

Very interested in your simplified schamatic for an OEM using the FTDI USB chip!

Again, thanks so much... hopefully I will be able to test tonight!

Chris Savage
01-21-2006, 02:17 AM
Weird, for some reason when I opened the PDF it only showed the second page, so I never even saw what you were connecting to. I just opened it from here at Parallax and it shows up fine. Now I see your programming board. BTW, the board I refer to is actually designed to program via the USB2SER development tool we carry. That works perfect. So now it's like having an SX in your design in that there's no programming circuitry per se, but there is a 4-pin header sticking up that the USB2SER plugs into. Eventually I hope to have a USB chip on-board though, which was the point of this. The main thing is that all the RS-232 circuitry is gone and reduced to just 1 or 2 components.

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

Steve Joblin
01-21-2006, 03:36 AM
Thanks for the update... did you see anything obviously wrong with the "Programmer"?

Chris Savage
01-21-2006, 05:56 AM
Didn't bother to trace that circuit. Sorry.

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)