Square wave problem

Cenlasoft · 2012-02-21 10:22

Hello,
I am trying to use an ultrasonic TX and I have attached a schematic showing the circuit I built. I simply using pin 0 to send out a square wave that is .5ms in duration with an interval of 20 ms. It is a continuous wave. It works for about 45 sec to 1 min and then stops. I checked this with a scope with the ultrasonic sensor and without. The prop simply stops sending the square wave. If I press reset on the prop it starts again.
Thanks for any help.
Cenlasoft

Circuitsoft · 2012-02-21 10:33

Can you post your code? The circuit looks fine.

MagIO2 · 2012-02-21 11:24

Wait nother 50 sec and it propably starts again. Sounds like a waitcnt-problem. But to be sure you should post the code - if it's more than a short program, attach a zipped version.

Another idea would be a recursion in your program which eats up the whole HUB-RAM.

groggory · 2012-02-21 11:52

Cenlasoft wrote: »

Hello,
I am trying to use an ultrasonic TX and I have attached a schematic showing the circuit I built. I simply using pin 0 to send out a square wave that is .5ms in duration with an interval of 20 ms. It is a continuous wave. It works for about 45 sec to 1 min and then stops. I checked this with a scope with the ultrasonic sensor and without. The prop simply stops sending the square wave. If I press reset on the prop it starts again.
Thanks for any help.
Cenlasoft

Try disconnecting this circuit completely...

Then running your prop program and puttnig your square wave pin on your scope and see if it'll keep working beyond the 45s-1min. If it is still working, then this circuit is the problem.

If this is the case I'm betting it has something to do with an interaction with the speaker/ transducer and your hex inverter. If you're using a piezo speaker perhaps you're hitting a natural frequency of it and it's overdriving the hex inverter and it's heating up and then going into shutdown? ...not sure.

What do you think?

Phil Pilgrim (PhiPi) · 2012-02-21 12:48

I'm voting for a software issue regarding use of waitcnt.

-Phil

Cenlasoft · 2012-02-21 14:27

Thanks for your suggestions. I tried sending a square wave using a signal generator set to 3.3 v and 40 khz. It did not fail. I have listed the code below:
{{
USTX.spin
Curtis Desselles
}}
Con

_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000

freqPin = 0
NewFreq = 40_000

Var
long stack1[32]

Obj

Pub Main

cognew(US_out(freq_Pin),stack1)

PUb US_out(fpin) | t

'' US pulse generator
'' -- uses ctra to modulate pin at 40kHz

ctra := (%00100 << 26) | fpin
frqa := 2_147_483 ' 40kHz @ 80MHz system freq
dira[fpin] := 1

t := cnt
repeat
outa[fpin] := 0 ' allow modulation
waitcnt(t += (clkfreq / 1_000_000 * 500)) ' on 0.5ms
outa[fpin] := 1 ' kill modulation
waitcnt(t += (clkfreq / 1_000 * 18)) ' off 19.5ms

Phil Pilgrim (PhiPi) · 2012-02-21 14:49

attachment.php?attachmentid=78421&d=1297987572

-Phil

Cenlasoft · 2012-02-21 15:51

Here is code properly displayed, thanks Phil:

{{
  USTX.spin
  Curtis Desselles
}}
Con

 _clkmode = xtal1 + pll16x
 _xinfreq = 5_000_000

 freqPin = 0
 NewFreq = 40_000 
  
Var
 long stack1[32]

Obj

Pub Main

  cognew(US_out(freq_Pin),stack1)


PUb US_out(fpin) | t

'' US pulse generator
'' -- uses ctra to modulate pin at 40kHz

  ctra := (%00100 << 26) | fpin
  frqa := 2_147_483                                             ' 40kHz @ 80MHz system freq
  dira[fpin] := 1

  t := cnt
  repeat
    outa[fpin] := 0                                              ' allow modulation
    waitcnt(t += (clkfreq / 1_000_000 * 500))                   ' on 0.5ms
    outa[fpin] := 1                                              ' kill modulation
    waitcnt(t += (clkfreq / 1_000 * 18))                        ' off 19.5ms

kuroneko · 2012-02-21 16:21

Pub Main

  cognew(US_out([COLOR="orange"]freqPin[/COLOR]),[COLOR="red"]@[/COLOR]stack1)

Cenlasoft · 2012-02-21 17:36

Thanks kuroneko, I don't know how I missed that. It works now. I wonder how it worked for 1 min before?
Cenlasoft

w8an · 2012-02-21 18:30

Seems like it would be a good idea to put some kind of procedure after the cognew(...) so that cog 0 doesn't go into some unknown free running state...

Pub Main
     cognew(US_out(freqPin),@stack1)
     repeat

kuroneko · 2012-02-21 18:30

Cenlasoft wrote: »

I wonder how it worked for 1 min before?

You basically placed your stack at address 0 in hub which definitely affects clkfreq (long[0]). If you'd waited slightly longer the pulse train would have restarted.

@w8an: cog 0 just stops when it reaches the end of the main method (provided no-one messed with its stack).

w8an · 2012-02-21 18:41

@w8an: cog 0 just stops when it reaches the end of the main method (provided no-one messed with its stack).

Noted

Cenlasoft · 2012-02-28 06:48

Thanks everyone for helping with this problem. In the circuit schematic (attached) that I posted, I want to tap in at one of the two traces going into the ultrasonic sensor. Basically I want to send a pulse (.5 ms, 20 ms interval) The amplitude is 10 vpp, At the tap point, I want to wait for a return pulse and measure the time of flight. I know how to do the spin code for that but, I don't want to burn my prop pin with the incoming signal pulse. The incoming signal pulse will be amplified using a 358 dual op amp which I have done already. It gives me a 2 vpp output. Any help with the circuit or code is appreciated.
Thanks
Cenlasoft

Square wave problem

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