NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Support Forum » Nerdkit Serial to USB wires?

December 31, 2009
by promethean
promethean's Avatar

Can I use the provided cable with another device? This devices simply calls for a GND, TXD, and RXD. (It's a AVR Butterfly) If so, which wires are which on the provided adapter? I know black is GND, but not what the others are. Thanks!

December 31, 2009
by xiangrui
xiangrui's Avatar

Yellow one is TXD.

December 31, 2009
by hevans
(NerdKits Staff)

hevans's Avatar

Hi promethean,

xiangrui is right, but when talking about RXD and TXD it matters which device you are talking about. Each serial device has an TXD (transmit) and RXD (receive). From the point of view of the computer the yellow wire is the TXD line, which is connected to the RXD pin on the MCU. Hope that clears thing up!

Humberto

July 12, 2010
by lsoltmann
lsoltmann's Avatar

My NerdKit USB cable stopped working for some odd reason the other day so I switch over to a Sewell USB-Serial cable and wired up a DB-9 connector to the breadboard. I looked up the serial pinout and am getting that pin 2 is Rx data, pin 3 is Tx data, and pin 5 is ground. Every time I try to upload code to the MCU is says

Connecting to programmer: .avrdude: butterfly_recv(): programmer is not responding

I've tried switching the Tx and Rx pins just to make sure I didn't wire them backwards but that doesn't seem to help. Tried reinstalling driver and cycling power. Any thoughts on whats going on here?

July 12, 2010
by Rick_S
Rick_S's Avatar

You may be running into a problem in the difference between "standard" RS-232 protocal Vs. TTL level protocol. The main differences from what I understand is that besides the voltage levels being higher with standard RS-232, the signal is also inverted.

There are several ways around this. One of the solutions is using an inverter like the NK guys did on their serial adapter prior to the one they currently use. Another way and one I've used a few times is through a Maxim MAX232 IC. This single chip handles complete RS-232 to TTL conversion very reliably. Depending on the variety it may or may not need a few capacitors along side it to act as charge pumps to raise the RS-232 voltage levels.

If you search Google for RS-232 to TTL you'll find all kinds of examples to help out in the design.

Good luck and keep us updated!

Rick

July 13, 2010
by lsoltmann
lsoltmann's Avatar

Thanks for the response Rick. I will definitely give it a try and let you guys know.

July 13, 2010
by Keyster
Keyster's Avatar

Isoltmann, Rick is 100% correct. he helped me with a similar problem the other day. i was trying to use a "china" bought USB to serial adapter (pl2303 based) with my nerdkit and it would not work. also, the nerdkit USB to Serial cable would not work with my GPS (which is standard RS232). i added the MS232 IC and now my Nerdkit will talk with the GPS (RS232) and the China purchased USB to serial converter. note: as expected i cannot program the nerdkit thru the MAX232 with the nerdkit cable.

my assumption here is the nerdkit supplied cable has a MAX232 built into the dongle. ;)

my thread has pictures if you need to see the setup.

link to other thread

July 15, 2010
by lsoltmann
lsoltmann's Avatar

Got the parts in for the adapter based on this website (http://www.seattlerobotics.org/encoder/aug97/cable.html) and that did the trick. Works great now. I appreciate all the help guys. On a side note I found this website about making your own PCB's at home that I thought look really cool. Thought you guys might like it if you haven't already come across it. http://www.riccibitti.com/pcb/pcb.htm

July 15, 2010
by Rick_S
Rick_S's Avatar

I used that method to make several boards, the most recent being one to hold a small USB based atmel board with other components. This device controls manual movement of a CNC milling machine where I work as well as behaves as a mouse for the attached PC. It is controlled by an industrial inductive joystick.

Here's a Link to the site with my project photo's.

Rick

Post a Reply

Please log in to post a reply.

Did you know that you need to think about wires differently when you're transmitting signals more than a few inches? Learn more...