A comment that I receive frequently about my Digital Setting Circles project concerns the fact that it uses a serial port rather than a USB port. I guess manufacturers don’t typically include serial ports on notebook computers or PDAs anymore. In my own defense, USB was just coming into common use when I designed this circuit about ten years ago, and USB is more complicated and expensive to implement.

Jimbo Harris actually adapted my decoder circuit to USB using a special cable from DLP Design. Jimbo was able to eliminate the MAX232 chip and the DB9F connector that way, but the net cost of the circuit was probably higher despite eliminating those parts. All the special cable really does is to make the USB port look like a serial port to the computer. There are plenty of commercial devices on the market that will do just that.

I’ve been told that USB-to-serial converters vary in terms of how well they work, which I find surprising. As far as serial interfaces go, the one in my decoder circuit’s about as simple as they come. It only runs at 9600 baud and only uses three serial lines (TX, RX, and GND) because it doesn’t use any hardware handshaking. There’s no twiddling of the lines at the hardware level. It really can’t get any simpler. It seems like, if a USB-to-serial converter works at all, it should work with my decoder circuit.

Are you using one of these USB-to-serial converters with my DSC circuit? Or perhaps with something else? If so, please leave a comment below and tell me about your experience. I’m going to experiment for myself here shortly–I ordered a $6 converter from Ebay (it’s hard to get cheaper than that, eh?) that I’ll try and post my results. And maybe I’ll consider doing a long-overdue update to my decoder circuit (but don’t hold your breath–it’s really hard to find the time for that kind of project these days).

8 thoughts on “Adapting to USB…

  1. Yes, I am trying this, but no luck so far. Before soldering, I am trying it on a breadboard…to no avail yet. The Laptop recognizes it, but I am getting no response via the Hyperterminal testing. That being said, I am just trying to get a response, since I wont get my decoders in for a few weeks. Should the circuit respond without the encoders attached? I’ll email a link to a snapshot of it wired up.

  2. OK thanks. This was looking bad until I decided that “If it ain’t talking, maybe the out is in?” I switched the pins for the USB tx/rx and all works now! Whew! Looks like a winner in my book, though I dont yet have the encoders for the full trial. You may want to let Jimbo know that on the bottom left of his schematic (red marked-up one), the “pin 6” and “pin 18” are on the wrong pins, per his actual connections. (see his later pic of the soldered connector) -Matt

  3. Dave, trying this with vista and having no success. How do I check this out? Any ideas, I’m kinda new at this. All I can tell you is that the PIC gets hot and your software doesn’t recognize the encoder hardware. I’ve downloaded ASCOM 5.5.1 and your driver and DSC.

    • Dan, it sounds like you might have made an error in construction. Check out the troubleshooting steps on the construction page and make sure all the parts are installed correctly, all the soldering is good (check the solder side of the board with a magnifying glass), cables are connected correctly, voltages are what they need to be, etc. The PIC shouldn’t get hot (but may warm a little).

  4. Dave,
    I found the problem. It works fine with the hyperterminal now. The printed board had a flaw in it and I had to re-soldered a connection.

    Can you tell me what the output for channel A & B are supposed to look like. I’m trying to hook up an optical encoder and I’d like to know what your interface is looking for.

    Thanks again


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