View Full Version : Burned my BS2 Interpreter :-( Please check my schematic and tell me it looks o

05-02-2007, 01:48 AM
Okay, I got a call from Chris today and he told me I accidentally burned my BS2 interpreter on my OEM BS2 module.· Apparently, the EEPROM was fine so I must've just pushed too much current through or something to the interpreter's I/O pin.

Anyways, I have spent about a half an hour putting together exactly what I want to do and if someone could just glance at this and tell me that THIS IS SAFE and that this WILL NOT·destroy the BS2 interpreter again!!· Thank you!!

Just to re-iterate Pin0 to Pin3 are ALL outputs, meaning they output from the BS2 module to the FPGA board.· The reason for the voltage-divider is because the FPGA board can ONLY accept 3.3V input and not 5V TTL high from the BS2.· Thank you!!!

HOWEVER, does anyone know how I can or if the BS2 can read a 3.3V logic HIGH from one of it's I/O lines?· Because I would like the FPGA to output to the BS2 as well.


Post Edited (l337hxr) : 5/1/2007 6:55:36 PM GMT

Chris Savage
05-02-2007, 02:16 AM
There doesn’t appear to be anything wrong with this schematic. Even with all 4 outputs to the FPGA high you will be drawing <8mA. Just be careful with your connections and double-check everything twice before powering it up. Take care.

Chris Savage
Parallax Tech Support

Mike Green
05-02-2007, 02:25 AM
This looks about as safe as these things can get. Accidents can always happen (like shorting an unused I/O pin to the +9V supply), but the design looks sound. In particular, you've got a current limiting resistor on the GPS output. Even if that goes to +12V, you're limiting the current into pin 9 to (12-5)/22K = 0.3ma ... a very comfortable level. Even if an FPGA input were to become a low output by mistake with the Stamp trying to supply a high output, the maximum fault current is 5/1K = 5ma ... again a very comfortable level.

The BS2 can indeed read a +3.3V logic high on one of its I/O pins. You probably should have a 220 to 1K protective series resistor there in case the Stamp accidentally has its pin changed to an output of the opposite level.

05-02-2007, 03:03 AM
You need a ground from the Garmin eTrex unit -- you may have one but it's just not shown?

Also -- are you recieving from the Garmin or sending to it or both? If you're sending to it, you'll need an additional line to the Garmin, using a MAX232 driver on that pin. That's assuming the Garmin does not support a 'TTL' mode.

05-02-2007, 03:05 AM
Thank you!!!!

yes, I forgot to put the ground line from the eTrex to the battery/bs2 ground...but it will be there!

I am ONLY receiving data from the eTrex...I am not sending anything back to the eTrex.

05-02-2007, 03:08 AM
Cool. Just make sure the line recieving stuff from the eTrex is set as an INPUT (which it is by default, and SERIN will set it and leave it that way too).