Scribbler 2 Level Converters

Mike Green

I know there have been problems with the "hacker's port" level shifters. I assume that a +5V pullup may help force the shifter into input mode. Anybody knows for sure? What would be a minimum value for such a pullup? Any other suggestions? I'm trying to attach a WiFly-RN-XV on an xBee 3.3V/5V adapter board. These use a 74LVC244A for buffering. I'd rather not have to bypass the level shifter.

Duane Degn

Mike,

The there are already 4.7K pull-ups on on the hacker port lines.

Phil posted a link to the level shifter datasheet in this thread (post #30). There was some discussion about the level shifter there as well.

This thread is about trying to us a Ping with a S2.

I strongly dislike the level shifter on the S2. It keeps me from using many devices I would like to use with the robot.

Mike Green

Boy, I'm just having all sorts of problems with the Scribbler's Hacker Port and the DB-9 Serial Port.

For the Serial Port, I'm using a Parallax USBto232 adapter. I can program the Scribbler, and transmit to the Scribbler, but nothing seems to come back from the Scribbler. I've used a variety of serial drivers including FDS, all at 9600 Baud. I wonder whether this is due to the RS232 interface circuitry "stealing" voltage from DTR for the negative supply.

For the Hacker Port, I'm trying to use the xBee 3.3V/5V adapter plugged into P4 and P5 to run a WiFly adapter. Sending data to the WiFly adapter from the Prop seems to work, but data from the WiFly adapter to the Prop doesn't get through. When I looked at the 3.3V/5V adapter schematic, there's a 1K serial resistor on the output of the 74LVS244A and that would limit the low voltage to the level translator, particularly with the 4.7K pullup. I shorted out the 1K resistor on the DOUT pin to the Hacker Port and that didn't seem to help.

Anyway, I'll appreciate any suggestions. I'm trying to make up a version of FemtoBasic for the Scribbler 2 that uses a WiFi connection for its console, supports most of the S2.spin calls, and stores up to 8 programs in the user area of the EEPROM, but I've got to get the hardware working first.

Duane Degn

Mike,

I'm using a Parallax USBto232 (Rev with my S2 and I can use PST with a terminal window just fine. I don't suppose this could be a PC vs Mac issue (IIRC you use a Mac)?

Is there something you'd like me to try using my USBto232/S2 to see if I can replicate the problem you're having?

I've seriously thought of removing the level shifter in my S2. However, part of the fun of a ready made robot is the ability to share programs with other robot owners. If I were to liberate my S2's hacker port, the programs I may write using devices connected to the hacker port wouldn't be usable to most S2 owners with their shackled unmodified hacker port.

Phil Pilgrim (PhiPi)

Mike Green wrote:

I wonder whether this is due to the RS232 interface circuitry "stealing" voltage from DTR for the negative supply.

That could be. If your comm program keeps DTR asserted while it's connected, TxD won't be able to pull the line low enough. Try to see if you can deassert DTR manually. Either that, or use a DB9 breakout board, break DTR, and just connect it to ground

-Phil

Mike Green

Thanks guys. I have another USBto232 adapter hidden away. That does work when I use PST with DTR deasserted. I still need to figure out how to get data from the WiFly adapter into the Prop without modifying the Scribbler hardware.