Hi, I'm doing a project and I am using the picaxe 18M and I need some inputs, such as when I managed to make the black line follower CNY70, just yesterday with the LDR program readadc and now I need to send a signal and seen trigger, I can program a signal 25microsegundos to be a frenuencia of 40khz and can be sent to a transducer?
Trigger to make signal 40kHz.
- Thread starter AKil
- Start date
Andrew Cowan
Senior Member
I'm not quite sure on everything you are asking, but this may help:
1) You can generate a continual output wave useing the pwmout command (on certain pins).
2) You can generate short pulses using the pulsout command (on all output pins).
Hope this helps!
A
1) You can generate a continual output wave useing the pwmout command (on certain pins).
2) You can generate short pulses using the pulsout command (on all output pins).
Hope this helps!
A
BeanieBots
Moderator
PWM (not PWMout) can be used to specify how many pulses are generated.
hippy
Ex-Staff (retired)
If I've understood correctly, the requirement is to send a short burst of 40kHz to an ultrasound transducer, that short burst consisting of eight 25us active pulses with 25us spacing between each.
I've seen similar eight pulse requirements in DIY ultrasound range finders but I've never seen any explanation as to why eight pulses are required; can more or less be used ? That may make things easier.
However many pulses, I don't think that's possible using just an 18M though it should be possible using PWMOUT plus some external logic, a counter and some gating to allow only eight pulses through.
It should be possible to use HSEROUT on an X1 or X2 with a 40,000 baud rate. HSEROUT 0,($55) would send five pulses ( start bit plus four data bits ), HSEROUT 0,($55,$F5) should send eight pulses with the required timing. It would be worth checking with a scope that the timing is correct but I would expect the data to be sent back-to-back.
An 18X can have its SFR's poked to send bytes at 40,000 using the internal UART and I think back-to-back data transmission can be achieved.
Getting the transducer activated is only half the story; detecting an echo and being able to determine the time is the other half, and probably more than half the work. All-in, it's easier to use a dedicated module like the SRF04 / SRF05 which is much easier to interface to.
I've seen similar eight pulse requirements in DIY ultrasound range finders but I've never seen any explanation as to why eight pulses are required; can more or less be used ? That may make things easier.
However many pulses, I don't think that's possible using just an 18M though it should be possible using PWMOUT plus some external logic, a counter and some gating to allow only eight pulses through.
It should be possible to use HSEROUT on an X1 or X2 with a 40,000 baud rate. HSEROUT 0,($55) would send five pulses ( start bit plus four data bits ), HSEROUT 0,($55,$F5) should send eight pulses with the required timing. It would be worth checking with a scope that the timing is correct but I would expect the data to be sent back-to-back.
An 18X can have its SFR's poked to send bytes at 40,000 using the internal UART and I think back-to-back data transmission can be achieved.
Getting the transducer activated is only half the story; detecting an echo and being able to determine the time is the other half, and probably more than half the work. All-in, it's easier to use a dedicated module like the SRF04 / SRF05 which is much easier to interface to.
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Hello i¡'m making my circuit with picaxe 18M he make puls 40Khz and MAX 232 to make 20 VPP with picaxe 18M i make pulsout 1,2 ( 1 = pinout and 2 is 20microseco but i need 25micros :S i dont know how to make that but i can't put 2.5) and with Max232 he make 0 to 10v and 0 to - 10 and transfer to trandsducer and when signal come i amplify that and i pulsin with picaxe i dont know that its correct :S or i can put a comparator when it detect i compare with 5 v signal and i connect with picaxe another theme is i want calculate the time with the picaxe , any command to clk? to know time , i have distance and propagation m/s 
http://www.rev-ed.co.uk/docs/srf004.pdf
http://www.rev-ed.co.uk/docs/srf005.pdf ( i have looked this but the other is already nice) i gonna test the 2^^
http://www.rev-ed.co.uk/docs/srf005.pdf ( i have looked this
but the other is already nice) i gonna test the 2^^BeanieBots
Moderator
The 18M does not support the "PWM" command which can stipulate the number of cycles so you will have to do it in hardware. (or use 08M/X2)
There are several methods you could use.
If you are not too worried about the exact number of cycles, (and I don't believe it to be critical), simply AND the signal with another output so that you can 'enable' the pulse stream for a fixed time period using pulsout.
Alternatively, feed the stream into a counter (eg 4017) and use a suitable Q output to dissable the stream (via a gate) after the required count.
There are several methods you could use.
If you are not too worried about the exact number of cycles, (and I don't believe it to be critical), simply AND the signal with another output so that you can 'enable' the pulse stream for a fixed time period using pulsout.
Alternatively, feed the stream into a counter (eg 4017) and use a suitable Q output to dissable the stream (via a gate) after the required count.
But pwm with 40Khz and 50% duty and 4017 to make 8 cycles are nice but i think the best solution are pulsout and pulsin :S but i dont know what is range and what i can do with range,, ihave picaxe 18M agfter that i amplify with Max232 and after that the signal go to transducer, to get echo i amplify signal and dont know if i can connect direly to the picaxe to receive pulsin :S , i can know the time with thwe picaxe with readclk?
hippy
Ex-Staff (retired)
PULSOUT may allow you to generate the required pulse but cannot execute quickly enough to give you the correct inter-pulse spacing. You will not get a 40kHz burst that way.
That's a physical, mechanical, component, circuit and implementation issue. The approach there is to prototype and see what results you get.
That depends on how your incoming echo detect circuit is designed. To use PULSIN you will need a pulse which is a measure of time between trigger and echo received. This may require additional circuitry.
READCLK will not be useful for determining the time between triggering and echo. You will have to use PULSIN or some other mechanism.
Then I would give a pulse output 40kHz rather a frencuency to 8 cycles of 40khz, after passing through the max232 and has what I need to be passed to 20Vpp and a transducer with a frequency of 40Khz, but I think as a pulse Pwmout or not pulsout which would be best suited for the reception I think that amplify and taken to picaxe serious enough, or so I'm doing a little circuit SFR004
Picaxe -> MAX 232 -> O ) ) ) ) ) ( ( ( ( ( O -> Amplifier -> Picaxe
I think that can be ok :S
Picaxe -> MAX 232 -> O ) ) ) ) ) ( ( ( ( ( O -> Amplifier -> Picaxe
I think that can be ok :S
hippy
Ex-Staff (retired)
I was assuming the intent is to make a cloned Daventech SRF04 ( or similar ) using a PICAXE rather than PICmicro ...
Schematic - http://www.junun.org/MarkIII/datasheets/SRF04.pdf
Timing - http://www.junun.org/MarkIII/datasheets/SRF04_timing.pdf
There are two issues there which have been recognised -
* The ability to generate the required 40kHz burst.
* The mechanism to determine the time between trigger and echo.
The dedicated PICmicro is capable of running at higher speeds and performing timing which the PICAXE by itself cannot. It is therefore necessary to use additional circuitry and/or alternative mechanisms to perform the same task.
This is also, I suspect, where the 'eight pulse' 40kHz burst idea originates from. Presumably there needs to be enough pulses to get the transducer outputting, but not too many to mask the echo.
I have seen a design on Google which use a single pulse and a very simple echo detect circuit as you suggest but I do not know how effective that would be.
The best way is to try it and see what happens. The only thing missing in your sugested setup is, how does the receiving PICAXE know when the pulse was sent ? It can read the ultrasonic pulse ( some time after it was sent ) but could not determine the time delay without an additional input. You also need a means to turn that time delay into a pulse which PULSIN can read.
Schematic - http://www.junun.org/MarkIII/datasheets/SRF04.pdf
Timing - http://www.junun.org/MarkIII/datasheets/SRF04_timing.pdf
There are two issues there which have been recognised -
* The ability to generate the required 40kHz burst.
* The mechanism to determine the time between trigger and echo.
The dedicated PICmicro is capable of running at higher speeds and performing timing which the PICAXE by itself cannot. It is therefore necessary to use additional circuitry and/or alternative mechanisms to perform the same task.
This is also, I suspect, where the 'eight pulse' 40kHz burst idea originates from. Presumably there needs to be enough pulses to get the transducer outputting, but not too many to mask the echo.
I have seen a design on Google which use a single pulse and a very simple echo detect circuit as you suggest but I do not know how effective that would be.
The best way is to try it and see what happens. The only thing missing in your sugested setup is, how does the receiving PICAXE know when the pulse was sent ? It can read the ultrasonic pulse ( some time after it was sent ) but could not determine the time delay without an additional input. You also need a means to turn that time delay into a pulse which PULSIN can read.
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i dont know that ,, in the circuit srf04 the trigger are coming out of the pic and pic only make 8 cycles of the triger? after that max232 make 20vpp? is that right?
But i want generate pulse in my picaxe and make 8 pulse of 40Khz but all program i see they use pulsout :O and u say me i can't make a puls of 40Khz with that.
,, in the circuit srf04 the trigger are coming out of the pic and pic only make 8 cycles of the triger? after that max232 make 20vpp? is that right? But i want generate pulse in my picaxe and make 8 pulse of 40Khz but all program i see they use pulsout :O and u say me i can't make a puls of 40Khz with that.
hippy
Ex-Staff (retired)
That is correct.i dont know that
That is also correct.
A single PULSOUT can give a 25us pulse ( SETFREQ M8
ULSOUT pin,5 ) but consecutive PULSOUT's will not give a 40kHz burst; the gap between pulses will be longer than 25us.Consecutive 25us pulses with 25us inter-pulse gaps can be generated with PWMOUT but you will need to enable and disable PWMOUT or gate those pulses to give just a number of pulses rather than a continuous stream.
If you want only eight pulses ( each guaranteed to be 25us with 25us gap ) you will almost certainly have to use some circuitry to ensure only eight pulses are issued.
hippy
Ex-Staff (retired)
You can use "PWMOUT 3,24,50WMOUT 3,OFF" to give a burst of pulses ( and at 8MHz you can adjust that to make it fewer pulses, or under-clock and get more pulses ), but if you want an exact number of pulses you will have to count them and use external hardware to count them and gate them, or provide some other pulse gating mechanism.
WMOUT 3,OFF" to give a burst of pulses ( and at 8MHz you can adjust that to make it fewer pulses, or under-clock and get more pulses ), but if you want an exact number of pulses you will have to count them and use external hardware to count them and gate them, or provide some other pulse gating mechanism.SilentScreamer
Senior Member
PWM runs in the background, pwmout off simply stops it from running.
hippy
Ex-Staff (retired)
You probably have an older manual. The one I have is "Version 6.8 02/2009", 221 pages. "PWMOUT pin,OFF" is listed on page 139.
But anyway; trust me, "PWMOUT 3,OFF" turns off PWM on a PICAXE-18M. Or you can try it for yourself with a LED+R connected between Output Pin 3 and 0V ...
#Picaxe 18M
Do
Pause 1000 : PwmOut 3,255,255
Pause 1000 : PwmOut 3,OFF
Pause 1000 : PwmOut 3,255,25
Pause 1000 : PwmOut 3,OFF
Loop
That LED should then show Bright-Off-Dim-Off etc.
Andrew Cowan
Senior Member
Up to 20 pin chips, you can only use PWMout on one specific pin.
28 pin chips have two PWM outputs.
A
28 pin chips have two PWM outputs.
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hippy
Ex-Staff (retired)
At the same time ? Probably not or you could simply send the same signal to two transducers.
In which case the PICAXE-14M which can route PWM using HPWM might be a good choice.
Now only i want to make a signal of 40Khz with picaxe to tranfer to MC1458 amplifier to put 20 Vpp to tranducer.
I want a command to make a signal of 40Khz if i make a pwmout 2,24,50 : pause 200 microseconds and i put pwmout 2,off its ok i calculte i cycle are 25 micros 8 are 200micros with that i can make 8 cycles no?
I want a command to make a signal of 40Khz if i make a pwmout 2,24,50 : pause 200 microseconds and i put pwmout 2,off its ok i calculte i cycle are 25 micros 8 are 200micros with that i can make 8 cycles no?
hippy
Ex-Staff (retired)
Each PICAXE command takes approximately 250us at 4MHz and for as long a PWMOUT is active, those 25us pulses will be coming out. How many pulses you will get depends on which PICAXE you are using, what PICAXE clock frequency you are operating at and where exactly the code is in program memory.
If you want an exact number of pulses you will need to count them or gate them in some way.
The easiest thing may be to set up a test program and look at what PWMOUT generates on an oscilliscope. Then decide if that is acceptable or not.
If you want an exact number of pulses you will need to count them or gate them in some way.
The easiest thing may be to set up a test program and look at what PWMOUT generates on an oscilliscope. Then decide if that is acceptable or not.
Andrew Cowan
Senior Member
That will create a 40kHz wave for 1.6 seconds. Is that what you want? To pause 200microseconds, you may want to use the pulsout command on an unused pin.
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