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Need help with serial servo controller — Parallax Forums

Need help with serial servo controller

reuben brewerreuben brewer Posts: 2
edited 2007-11-10 22:46 in General Discussion
Hi, I'm trying to use the parallax serial servo controller (http://www.parallax.com/detail.asp?product_id=28023) and am having problems. I'm using an E128 (http://www.freescale.com/files/microcontrollers/doc/data_sheet/MC9S12E128V1.pdf?fpsp=1) to generate a serial signal that goes to the servo controller. I've plugged my RS-232 output into my computer's serial jack and have confirmed that I'm sending a properly-formatted servo position command of the form

!SC channel_byte ramp_byte pwm_pos_low_byte pwm_pos_high_byte CR

@ 2400 Baud, 8 bit data, 2 stop bits.

I've connected 5v, gnd, and the serial line from my E218 to the servo controller, and I see the controller's green light blink when I send it a command. However, when I scope the channel's signal, it just stays at 1.5mS regardless of what I command it to...

Any thoughts on why this isn't working?

Much thanks!

--Reuben Brewer
rdbrewer@stanford.edu

Comments

  • reuben brewerreuben brewer Posts: 2
    edited 2007-11-06 03:47
    Oh, I forgot to mention: For the "!SC" header, I'm sending the hex equivalent of each ASCII character: so "!" = 21 (hex) , "S" = 0x53 (hex) , and "C" = 0x43 (hex). So I'm sending

    0x21 0x53 0x43 channel_byte ramp_byte pwm_pos_low_byte pwm_pos_high_byte 0x0D.
  • jeffewongjeffewong Posts: 7
    edited 2007-11-07 06:02
    maybe you can try adding a pull up resistor 4.7k ohm to +5V at the signal of PSC. i faced similar problem before. After adding a pull up resistor, it works fine.


    connection:

    +5V
    |
    4.7Kohm resistor
    |
    |
    serial in of PSC(white)
  • rockerboyrockerboy Posts: 14
    edited 2007-11-10 22:46
    jeffewong said...
    maybe you can try adding a pull up resistor 4.7k ohm to +5V at the signal of PSC. i faced similar problem before. After adding a pull up resistor, it works fine.


    connection:

    +5V
    |
    4.7Kohm resistor
    |
    |
    serial in of PSC(white)
    I already have 10K connected to my 5V supply. Did you connect 4.7K apart from the 10K? I have attached my circuit diagram.
    bmp
    226K
    PC.bmp 226.1K
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