output pulses

LW

I have a basic stamp 2 I wish to make it generate a pulse out on one pin I need it to be around 360 hz the complicated bit is I need it to not generate every 36 pulse. So 35 pulses then a missed pulse. Any ideas welcome. Lynton

stamptrol

So, what have you tried so far?

Its always easier to get help if you show folks what you've attempted yourself.

Cheers,

Mike G

See the PULOUT command in the STAMP manual.

Mike Green

The PULSOUT statement generates a pretty accurate pulse, but doesn't generate the space between the pulses. What you can do is set aside an I/O pin so it's not connected to anything and use that with a PULSOUT statement to produce the space between the pulses. Let's say that 360Hz is a 3ms period (roughly) and you want a 1ms pulse. The unit for the PULSOUT is 2us on the BS2. You'd have this for one pulse:

pulseWidth CON 500
spaceWidth CON 1000


PULSOUT pulsePin,pulseWidth
PULSOUT extraPin,spaceWidth

You'd repeat this 35 times, then the 36th time you'd use

PULSOUT extraPin,pulseWidth+spaceWidth

You could also put the two PULSOUT statements in a FOR / NEXT loop to get the 35 times, but you'd have to adjust the pulse widths slightly to account for the overhead of the FOR / NEXT statements. You'd have to adjust the timing anyway to account for the overhead of the PULSOUT statements.

vaclav_sal

Mike Green wrote: »

pulseWidth CON 500
spaceWidth CON 1000


PULSOUT pulsePin,pulseWidth
PAUSE 2

.

Mike , would this accomplish the same given / assuming the 1 ms on / 2 ms off setup is OK for 35 pulses and than wait 3 ms

PAUSE 3
for the 36th pulse ?
Vaclav

Mike Green

Yes, but PAUSE is a coarse delay with a resolution in milliseconds while PULSOUT provides a fine resolution (2us).

Phil Pilgrim (PhiPi)

Lynton,

I believe this will do what you want:

' {$STAMP BS2}
' {$PBASIC 2.5}

OUTPIN  PIN 0
DUMMY   PIN 1
BAUD    CON 16384 + 227

DO
  SEROUT OUTPIN, BAUD, [REP $f0\35]
  PULSOUT DUMMY, 868
LOOP

It creates the pulses by sending a stream of characters with SEROUT using inverted mode.You can adjust the width of the pulses by changing the $f0 to, say, $f8 for narrower pulses, or $e0 for wider ones. Because, as Mike points out, PAUSE is so coarse, the inter-burst gap has to be filled with something more precise. This entails using an extra pin for a PULSOUT which, on the BS2 has a resolution of 2 us.

It's always hard to predict exactly how much delay the PBASIC interpreter's overhead will add to the timing. This is one case where having a good scope helps, since you can twiddle the constants until everything comes out just right. Here's a trace from my scope, showing the OUTPIN output on channel one and the DUMMY output on channel two:



-Phil