Servo Controller

mattlorenzjr

I am working on a project where I need to control 8 or 10 servos from a PC.

I have this limited experience with controling servos from a PC:· PC->BS2->Servo.

I see there is a Servo Controller Board available in Serial and USB.

Does anyone have experience with this/these Servo Controller boards and are they intended for the Stamp to send signals to the SCB or is the intention for the SCB to get its signal straight from the PC?

I am looking for the easiest/most-straight-forward way rather than least expensive.

Mike Green

The USB Servo Controller is intended for use with a PC although it also has the ability to be used with a Stamp or other 5V logic microcontroller. Download the documentation for both the USB version and the serial version. The serial documentation describes the commands used while the USB documentation describes the use of a provided PC program to control servos.

FireHopper

I use the new psc in a project, It's connected to a basic stamp, seems fine. I can also connect it to my mac to check endpoints with a program I wrote.

mattlorenzjr

Thanks for the FAST response!· I really appreciate the help.·

I read the PDF Manual for the PSC Serial, which states that the PSC will take input from an RS232 Device; however the manual assumes the input is from a Stamp.

This statement:
"This device can be connected to a PC serial port using a MAX232 line driver. The circuit isn't supported by Parallax, but it's possible to make this connection with a few dollars of parts."
On this Page:
http://www.parallax.com/Store/Robots/RoboticAccessories/tabid/145/List/1/ProductID/376/Default.aspx?txtSearch=servo+controller&SortField=ProductName%2cProductName

Confuses me somewhat.· Does this mean I need this MAX232 line driver, or is it that I can just fashion my own Communication Cable PC's-DB9->PSC-Serial-In-Pin?

I found this page: http://forums.parallax.com/showthread.php?p=640507·which seems to indicate that I cannot just fashion my PC's-DB9->PSC-Serial-In-Pin, but I had better wire up this diagram or use a MAX232.

I·am going to use·RS232·vs. the USB because I am already familiar with Tx/Rx RS232 via VB6 but I am not at all familiar with coding for USB.

Basically, for reassurance, what is your take on wiring RS232 from PC to the PSC?· Just run it, use the suggested diagram, or use a MAX232?· Again, easy-straight-forward is favored over saving money.

Matt
·

Mike Green

You have to use a MAX232 or equivalent. There are some other circuits that can work, but you can't just connect the PSC to an RS232 port. It'll damage the PSC. One example of a non-MAX232 adapter is from SparkFun: www.sparkfun.com/datasheets/Prototyping/RS232-Shifter-v2.pdf. This is bidirectional and requires some changes to work with the shared I/O line on the PSC. Better to use the example you noted in your links.

Post Edited (Mike Green) : 6/8/2008 8:12:58 PM GMT

mattlorenzjr

Excellent, most excellent.

I do see online that the MAX232 is not very expensive, especially since an hour ago I thought I was going to have to put a Stamp in the mix anyhow.

Really, controlling 16 Servos with a MAX232 & PSC is unbelievable for the little cost!

I am controlling 8 or 10 outlets by mechanically connecting·lightswitches to servos to get the on-off motion necessary.

Sub Question: I do not see 120V relays on Parallax, but I am wondering, generally, how does cost of a servo + light switch ~$13.00 stack up against Relays and the subsequent necessary Relay Controller Board?

Matt

Mike Green

Good sources for relays include Jameco, Mouser, and Digikey. If you need to switch less than 5A, Jameco has a solid state relay from Crydom for about $13 that can be controlled directly from a Stamp I/O pin. If you want to use a conventional relay, you'll need a switching transistor and a diode as described in Parallax's Industrial Control tutorial around page 96. Go to the main Parallax page, choose the Resources tab, then Downloads, then Stamps in Class Downloads.

FireHopper

the usb makes a use of a usb > serial adaptor built into the board, and can be accessed like a serial port. I access it like a serial port on my mac.
I would think it would be the same on a pc as long as you have the ftdi drivers. I had to go tothe ftdi website for the mac drivers. I know it works, because my program can send serial commands to the controller.

mattlorenzjr said...
Thanks for the FAST response!· I really appreciate the help.·

I read the PDF Manual for the PSC Serial, which states that the PSC will take input from an RS232 Device; however the manual assumes the input is from a Stamp.

This statement:
"This device can be connected to a PC serial port using a MAX232 line driver. The circuit isn't supported by Parallax, but it's possible to make this connection with a few dollars of parts."
On this Page:
http://www.parallax.com/Store/Robots/RoboticAccessories/tabid/145/List/1/ProductID/376/Default.aspx?txtSearch=servo+controller&SortField=ProductName%2cProductName

Confuses me somewhat.· Does this mean I need this MAX232 line driver, or is it that I can just fashion my own Communication Cable PC's-DB9->PSC-Serial-In-Pin?

I found this page: http://forums.parallax.com/showthread.php?p=640507·which seems to indicate that I cannot just fashion my PC's-DB9->PSC-Serial-In-Pin, but I had better wire up this diagram or use a MAX232.

I·am going to use·RS232·vs. the USB because I am already familiar with Tx/Rx RS232 via VB6 but I am not at all familiar with coding for USB.

Basically, for reassurance, what is your take on wiring RS232 from PC to the PSC?· Just run it, use the suggested diagram, or use a MAX232?· Again, easy-straight-forward is favored over saving money.

Matt