How long does PULSIN take?

Armored Cars

When in manual mode my car is really jerky, how long does PULSIN take so I can adjust PAUSE accordingly?

MANUAL:
··· DO
····· PULSIN 2, 1, mansteer
····· PULSIN 3, 1, mandrive
····· IF mansteer<400 THEN GOFWD
····· PULSOUT 0, mansteer
····· PULSOUT 1, mandrive
····· PAUSE 20
··· LOOP

steve_b

What version of stamp are you using?

If you are running Pbasic...hit F1 and look up PULSIN.·

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Steve
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Armored Cars

Im using a BS2 and I did look, all I found was a chart which stated the maximum pulse width, which Im assuming is not how long it takes since a 140 ms pause is much longer that how fast my car was jerking.

allanlane5

I believe 'PULSIN' waits for the beginning of the pulse up to 131 mSec, then waits for the end of the pulse up to 131 mSec.

And 140 mSec is like 1/10 second. I believe you can 'percieve' that short a time -- but not enough to say "is much longer than how fast my car was jerking".

One way to minimize this would be to only do a single PULSIN per loop. Thus:

CheckMan VAR BIT

MANUAL:
· DO
··· CheckMan = ~CheckMan
··· IF CheckMan THEN
····· PULSIN 2, 1, mansteer
····· PULSIN 2, 1, mansteer
··· ELSE
····· PULSIN 3, 1, mandrive
····· PULSIN 3, 1, mandrive
··· ENDIF
··· IF mansteer<400 THEN GOFWD
··· PULSOUT 0, mansteer
··· PULSOUT 1, mandrive
···' ·PAUSE 20
· LOOP

Now, if you are driving pins 2 and 3 with the output of a Servo reciever, it is probably repeating at a 20 mSec rate -- but you don't know when you start to sample it.· It could be 40 mSec worst case.· If the Servo pulse has already started before you start to sample it, you may read it as 'too short'.· Outputting a 'too short' servo pulse could make you jerky.

One solution could be to read the servo signal twice, and take the second signal as the one you'll keep.· That should·guarantee that the second signal gets both the start·AND end of the pulse.· Then you probably don't need a 'pause' at all, because reading the servo signal will take that much time.

OK, I've now updated the code above to do the 'read servo input signal twice'.· You still want to read only steering, or only drive, each time through the loop, but you can update both servos each time through the loop.· This should work.

Post Edited (allanlane5) : 12/14/2004 8:36:46 PM GMT

Shawn Lowe

Check out Tracy Allens website: www.emesystems.com. He probably has a good write up on the time of execution of the pulsein command.
Shawn Lowe

Armored Cars

I think Ill use relays to switch the servos to manual control, but I have another question.
After about a minute of using the code

MANUAL:
DO
PULSIN 2, 1, mansteer
PULSIN 3, 1, mandrive
IF mansteer<400 THEN GOFWD
PULSOUT 0, mansteer
PULSOUT 1, mandrive
LOOP

mandrive will start to equal mansteer. I didn t have enough wires to run anything to pin 3, but after awhile it starts copying pin 2.

What this code is doing is taking the pulse from an RC reciever and sending it to the servos.

allanlane5

If pin 3 is 'open', i.e. nothing connected to it, you have what is called a 'floating input'. These can pick up RF from the air really easily -- typically 60 HZ AC flourescent lamp noise.

And WHAT DO YOU MEAN you are doing a 'pulsin' on a pin with nothing connected? That's going to time-out every time! That's a 131 mSec delay in your program every loop. If you HAVE no input signal, don't try to READ an input signal.

At least tie the pin to ground with a 22 Kohm resistor, to give yourself a 'soft' ground signal.

Armored Cars

I went ahead and added the extra PULSIN because I would be using it once I got the wires to hook it up, I didnt realize it took any longer. That was the problem though, thanks.