40 KHZ pulse train adain!!

[Summertown]

I went thru this a while back...
I need to generate a 40 khz pulse train for an ultrasonic measuring device for measuring the water in a tank.
Previous advice was to use an external inverter, easy enough. That was until Mr Google found this gem http://www.robot-electronics.co.uk/htm/srf04tech.htm Looking at the diagram the devive gets in & out of phase signals from pins 2 & 3.
I am using a 28x.
For those who are familiar with the Microchip devices, is this possible on a picaxe.
Gonzo

 

[eclectic]

To make life simpler, have a look at this link.
They work perfectly.

<A href='http://194.201.138.187/epages/Store.storefront/?ObjectPath=/Shops/Store.TechSupplies/Products/SRF005' Target=_Blank>External Web Link</a>
e.

 

[Summertown]

It is the same item, the 05 being an updated 04. I still would like to know how they do it, even with an overclocked chip.
Gonzo

 

[eclectic]

My apologies.

I assumed (wrongly it seems), that this was
a separate question to your 03 June posting
and that you were simply looking for a rangefinder.
e.

 

[Summertown]

That's OK, I need to build a bundle of these things, a sib
single 28X solution would be great.Gonzo

 

[snailinstruments]

Try the PWMOUT command.
Josef

 

[hippy]

<i>Looking at the diagram the devive gets in &amp; out of phase signals from pins 2 &amp; 3... is this possible on a picaxe </i>

No. The PICmicro there is almost certainly bit-banging the two signals out rather than using any on-chip hardware. A 40kHz output means switching the output pins every 12.5uS, which is easy enough on a PICmicro, but not for a PICAXE without using PWMOUT, and that is only a single signal, so hence the need to use some external hardware inversion to create an out of phase signal.

 

[hippy]

Q : Do you need two out of phase signals ? Have you considered just a single signal with the transducer to 0V ?

 

[Dippy]

If my addled memory serves me at least one of the Devontech u/s device made cunning use of a RS232 (Max type) to pump-up the voltage to the U/s transducer - maybe thats why they need 2 pins(?)

And the SRF05 is an improvement on the SRF04. After BB's post t'other day I got a couple and they (with careful mounting) provided pretty accurate ranging at 5m outdoors on a windy day.
I've seen an ic somewhere to control up to 6 from serial PICAXE 2-wire - much cheaper than a bundle of SRF08/10.

And with the SRF05 from Devontech at &#163;14 odd I couldn't be arsed to try and make my own.

 

[hippy]

That SFR04 mentioned in the first post seems to use an RS232 buffer ( I hadn't paid any attention until mentioned ), which is a clever way of putting 24VPP across the transducer. That no doubt maximises range over the normal out of phase 10VPP, or single phase 5VPP.

 

[Summertown]

Hi Hippy.
Bloke thanks for that gem. This is the question I have banging on about for ages. Looks like I am off to the bookshop for a book on PICmicros and/or use the Rev ed card.