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Pololu USB to Serial adapter question — Parallax Forums

Pololu USB to Serial adapter question

lwcyblwcyb Posts: 13
edited 2015-02-18 10:09 in BASIC Stamp
I'm trying to save space on a board of mine that is incorporating a BS2px by using a USB-to-serial breakout adapter board. The USB board in question is this one here: https://www.pololu.com/product/391

I'm having trouble communicating with the Stamp when I go to upload my program. I've switched the RX and TX lines around, hoping for a simple mistake like that, but to no effect. The error I get is "No Basic Stamps found on Com port #xx". I am getting both feedback and echo statuses as "Yes". The description suggests the logic levels should be compatible with the Basic Stamp but maybe I am understanding this incorrectly.

I would appreciate any advice on the issue, thanks.

Comments

  • Martin_HMartin_H Posts: 4,051
    edited 2015-02-16 06:54
    That is a USB to TTL serial adapter, which use 0 volts and either 3.3 or 5 volts. Except for the OEM models the stamps use RS-232 voltages which are inverted true to false, and use positive and negative voltages. At the very least you'll need to use something like a hex inverter to correct the truth values, and possibly a level shifter. A max-232 IC has all of this in one package, but requires some external capacitors to create the negative voltages.
  • ercoerco Posts: 20,256
    edited 2015-02-16 07:36
    You also need an ATN line connection. Many (if not all) of the Prolific chips work do not work on the Stamp. The one you linked to shows a CP2101 (?) in the photo. FTDI chips are generally the ones which guarantee success, as many forum posts have discussed: http://forums.parallax.com/showthread.php/155520-Serial-to-USB-adapter

    https://www.pololu.com/product/1606

    If you only care about a small footprint on your board, you can use nearly any 4-pin connector to hook up an external USB serial adapter. I often use a simple 4-pin male header immediately beside the Stamp, as shown below.

    attachment.php?attachmentid=103389&d=1376708665
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2015-02-17 09:20
    If you were trying to integrate a BASIC Stamp into your design (not using a module) then you could use the concepts described here: http://www.savagecircuits.com/bs2oem

    However, with a module an RS-232 interface is required as mentioned.
  • lwcyblwcyb Posts: 13
    edited 2015-02-18 10:09
    Got it. Thanks guys.
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