Servo and BS2P

Newzed

I'm having a bit of a problem running my servo from a BS2P.· I remember the duration of the pulsout has to be increased because of the .8us unit of duration.· Is there anything else?

Sid

Shawn Lowe

What problem are you having exactly?

Shawn Lowe

Jon Williams

Nope, nothing else. Remember that when you use a servo you should initialize the pin like this:

Reset: 
  LOW ServoPin

That will force the pin low so that later PULSOUT instructions will go low-high-low as required by the servo.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA

Newzed

Jon, this is really weird.· This is part of my keyboard interface program - I was running the whole thing on a BSE, then switched to BS2P so I could use my piggyback DS1307.

When I send a command to run the servo, it just moves a tiny bit.· By putting in a bunch of debugs I was able to determine that it is acting as if it were resetting the Stamp.· I put a 470uf cap across the servo power leads but that didn't help.· I can try to run the servo in either direction but it always moves that tiny bit, and always in the same direction.

I commented out the servo instructions, hooked an LED from the servo command line to ground, removed the servo, took the servo line high for 2 secs, then low, and everything worked perfectly.

Here is a snippet of code from the bank that runs the servo:

pos = 750······ 'same as 600 on a BS2
SEROUT lcd, baud1,10, [noparse][[/noparse]"A", "Running 1",13]
low serv1
FOR com = 1 TO 101
PULSOUT serv1, pos····· ·'Goes beserk right here
STOP
PAUSE 20
pos = pos + 2
NEXT
SEROUT lcd, baud1, 10, [noparse][[/noparse]"C", "Enter command",13]
PAUSE 100
com = 1
RUN 0

I inserted the STOP after the PULSOUT command but it had no effect.
The program just jumped back to the very beginning of Bank 0 as soon as the servo twitched.

Hope you see something - if nothing else I can go back to the BSE and see if·everything still works.· I'll have to switch the clock bank back to a [url=mailto:D@1302]DS1302[/url].

Sid

K de Jong

Hi Sid,

Is your power supply OK ?? Do you have too many 'consumers' in your system ??

Regards,

Klaus

Newzed

Don't think so, Klaus.· Put a 470uf cap across the servo power leads but that didn't help.· Have no idea how much a servo draws when it starts - everything worked fine when I was on the BSE.· Tomorrow I'll hang a scope on the power lead and see if the voltage takes a downward plunge.· I really have a feeling that is the problem.· Disconnected the LCD display but that didn't help.

Sid

Bruce Bates

Sid -

Just as a test, try pulling the servo power lead off of the Stamp carrier board (presuming that's where it's getting its power) and run it from a battery instead. Make sure to add a common ground path. I think it will work with a dual power set-up.

If it still fails, the servo may be mechanically jamming and comsuming large amounts of current. Something as simple as bound up gears can cause that kind of thing to happen.

The old trick of putting DEBUG "Starting" at the head of the program is always helpful. If you see it displayed more than once you know the Stamp is being reset.

Regards,

Bruce

Newzed

Klaus and Bruce, as I suspected it was the power to the servo.· I tried a 3300uf and that didn't help, so I added a separate 7805 just for the servo running off of Vin.· Now it works perfectly.· Had to use pulse durations·of 1000 and 2250 to make it go right and then left.· Since this is a continuous rotation servo, I simply used a for/next loop to control the number of pulses the servo got.· I also increased the pause from 20ms to 40ms to slow the servo down a bit.· Even at 40 it runs smooth as silk.

Sid