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View Full Version : Build a cable?



leetman
09-07-2008, 06:09 AM
I've been thinking of buying myself a BS2 OEM kit and wondered if I could use an ordinary serial cable to program it. Also, is it possible to remove the standoffs and plug the board in directly? Thx.

erco
09-07-2008, 07:50 AM
Yes and yes. I taught a class where several students plugged their BS2 Homework boards directly into the serial port on the back of their laptops without using any cable at all. It depends on your computer's particular physical port layout whether you have room to plug it in or not.

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"If you build it, they will come."

leetman
09-07-2008, 08:01 AM
Sweet! Thanks, erco!

leetman
09-08-2008, 01:43 AM
Also, the OEM cannot use power from the DB-9 connector, right?

Mike Green
09-08-2008, 01:51 AM
Serial ports are not designed to supply power. Sometimes you can "steal" a few mA from the handshake lines.
Usually that's used to provide the minus supply for proper RS232 operation. It would be really iffy to try to power
the OEM Stamp from that.

leetman
09-08-2008, 01:54 AM
Hmm. My thoughts exactly. Which means the BS2 OEM needs external power from the Vdd/Vin pins to program?

erco
09-08-2008, 02:02 AM
Yessiree. Although I haven't used the OEM board myself, I'm betting it behaves similarly to my BoE & Homework boards, although those OEM discrete components might require a bit more power. You'll need a clean +5V on Vdd or 7 volts or more on Vin to power your Stamp. On occasion, my Stamp will continue running & debugging even after I disconnect its 9V battery. So obviously, it is getting marginal power through the programming cable, but per Mike, you can't can't on that reliably or for start-up, or to power any external circuitry.

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"If you build it, they will come."

leetman
09-08-2008, 07:20 AM
But would it be possible to use the DTR, etc. lines and regulate them to power the BS2? I mean, it needs only 3 mA

erco
09-08-2008, 07:29 AM
You can certainly try for your application! If you have no external circuitry drawing more power, 3 mA may be doable, supplied through the cable. Keep in mind, there is a brownout regulator which will shout down the stamp if power falters temporarily. Might be worth having a large cap trickle charging in the background to provide temporary power during transients.

Of course, as long as you're tethered to your computer, you can also pull +5V off of a USB port to power something big. I have a couple of those new USB Ni-MH cells that recharge off a USB port. They get downright HOT during charging, so there is a lot of current available there.

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"If you build it, they will come."

leetman
09-08-2008, 07:33 AM
USB was always an option, but I didn't want two plugs going into the computer. I don't know, I still don't own a BS2 as of yet.

erco
09-09-2008, 08:50 AM
All this jaw-flappin' and you don't own a BS2?

Have some respect for yourself. Man up & get one. http://forums.parallax.com/images/smilies/smile.gif

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"If you build it, they will come."

leetman
09-09-2008, 11:25 AM
I know, I know. I'm planning to get one quite soon.

Dgswaner
09-09-2008, 11:39 AM
this is from the Stamp FAQ located here:

http://www.parallax.com/Portals/0/Downloads/docs/prod/stamps/basicstampfaq.pdf

"The BS2-IC consumes 8 mA in running mode and 100 μA in sleep mode, not including any circuitry on
the I/O pins."

and I think it's referring to the STAMP 28 pin package not the OEM kit. I have a BS2 oem. it's a good kit and easy to assemble... but I'd get the bs2SX oem kit. it's a bit more bang for the buck.

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DGSwaner

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"When in doubt, use C4" - Jamie Hyneman, Myth Buster

leetman
09-09-2008, 11:41 AM
I put that into consideration already. But I found that the BS2SX is something I'd really want, but the BS2 suffices for my applications and uses less power. I'd suspect the BS2 has similar current draw characteristics.

leetman
09-11-2008, 10:41 AM
The sale that just started really gives me a reason to buy one now! w00t!