Pololu micro serial servo controller and Gumstix Verdex

Support Servo controllers and servos
1

Setup:
Servo controller attached to verdex BTUART (ttyS1, 9600 baud, 3.3v etc), powered by tap taken from verdex 5vdc wall supply input

Symptom:
Servo controler powers up corectly then enters error state on first full command, green led indicating line activity is “feeble”.

Have tested:

  1. Servo controler using pololu usb to serial bridge (ttyUSB0, 9600 baud, 3.3v etc), works no problem,
    green led indicating line activity is “stronger”.

  2. Verdex BTUART using pololu usb to serial bridge (ttyUSB0, 9600 baud, 3.3v etc), works no problem.

I suspect a weak signal drive from the verdex BTUART (insufficent for 5vcc servo controler), but lack the test gear to confirm.

Does anyone have any experience with this pairing? or know why the servo controler works for one nominaly 3.3v input but not the other?

2

Hello,

The CP2102 used in our serial adapter tends to give above 3.3 V signals. Your 3.3 V device might give less. The idle state of the serial line is high, so you should be able to check the level with just a multimeter.

If the level is too low, you’ll have to insert a level shifter between the two. If your level is close to the threshold, you might be able to get away with just a resistor or diode trick (the serial input has a pull-up resistor of 4.7k or so) to bump up the voltage a bit. Also the RS-232 input just goes into a transistor-resistor inverter, so if you can get an inverted version of your serial signal, you can connect to the RS-232 input.

- Jan