Using ServoPAL /ServoPAL functionality in custom board

Morrolan

Hi guys,
I was just wondering if there are any IC's out there which can do something similar to the ServoPAL, i.e. send a pulse from a BS2 and then let the ServoPAL IC hold the relevant position, rather than the BS2 having to continually pulse to hold that position?

What I have are 2 touch switches, one for left, one for right.

PseudoCode: (sorry not near my code)

ServoPosition  var byte (127 being centred)
ServoPosition = 127

If Left = Pressed then ServoPosition = ServoPosition - 5
Pause 20ms
repeat until Left = NotPressed then [b]hold position[/b]

And the same for Right.

My question is, can I use something similar to the ServoPAL to hold the position until either left or right is pressed again?

The reason I can't really use the ServoPAL is because space is at an EXTREME premium, as the device is worn on the body and forms part of a medical orthosis. (Sorry I'm not allowed to go into more detail )

I suppose the other alternative is to program the BS2 to pulse at that interval, but I haven't explored possible ways to code that yet.


Many Thanks in advance.
Morrolan

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Flying is simple. You just throw yourself at the ground and miss.

"I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
Stephen Hawking

RobotWorkshop

Hello,

You may want to checkout the chip in the following thread:

http://forums.parallax.com/forums/default.aspx?f=15&m=192088&g=197737#m197737

It looks like it might do what you are looking for.

Good luck,

Robert

Mike Green

1) A servo motor only requires a control pulse about every 20ms and many control programs can work in a cycle where a servo control pulse is generated at least every 20ms and the program does some sensor reading and computation in between the servo pulses. Look at some of the programs for the BoeBot for examples of this (like in the Robotics tutorial that you can download from Parallax).

2) The ServoPAL or the PWMPAL takes over this "every 20ms" cycle so that the Stamp can do more complex computation or sensor interfacing that might take more than 15-20ms.

3) Any small microprocessor could be programmed to do the same sort of thing. Microchip and TI both have some very small 6-pin SMT microcontrollers with an internal clock that could be used for this same sort of thing and take up very little space and very little power. You'd have to do your own programming, but this particular application is not very complex. Your program would have to initialize itself to not put out a pulse until it sees a positive-going pulse on one input line, time that pulse, then begin to output a pulse of the same width on an output line. If other input pulses come in, their width replaces the current one used for output pulse production. The output pulses are repeated every 15-20ms once started.

Bean

Mike,
I know of the PIC10F parts, but I didn't know that TI had any 6 pin devices. You don't happen to know of any part# for them do ya ?

Bean

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
www.iElectronicDesigns.com

·

Mike Green

Bean,
I checked my files, it's just Microchip that has the 6 pin devices (PIC10F). Sorry.
Mike

Bean

Darn, you got my hopes up Mike.
I was hoping for a SOT23 controller that had a little EEPROM.

Bean

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
www.iElectronicDesigns.com

·

Steve Joblin

would this chip help? http://www.selectronic.fr/includes_selectronic/pdf/Ferrettronics/FT639.pdf

If so, I know Jameco sells it for about $10