need help explaining this circuit!

[legolaslee]

Hi guys. I need help with this circuit. I don't understand how does it work. Can anyone explain to me this circuit? Its the ultrasonic transmitter by the way, and IC 3 is 4093. VR4 is used to adjust the frequency to 40 khz.

https://img140.imageshack.us/my.php?image=schtranspk9.jpg

 

[ericgibbs]

Hi guys. I need help with this circuit. I don't understand how does it work. Can anyone explain to me this circuit? Its the ultrasonic transmitter by the way, and IC 3 is 4093. VR4 is used to adjust the frequency to 40 khz.

https://img140.imageshack.us/my.php?image=schtranspk9.jpg

Its a 40KHz pulse generator using the 4093 which drives a push pull transistorised output stage for the transmitter module.

 

[legolaslee]

Hmm. What about the NAND gates? What does it do?

 

[ericgibbs]

Hmm. What about the NAND gates? What does it do?

The bottom section of the 4093 inverts the pulses from the pulse generator so that the transistors are driven by th opposite phases of the pulse, compared to the top transistors,,,push pull,

 

[legolaslee]

Hmm. Whats the meaning of transistors driven by the opposite phases of the pulse?
IC3/2 and IC/3 are used to generate a pulse?

 

[ericgibbs]

Hmm. Whats the meaning of transistors driven by the opposite phases of the pulse?
IC3/2 and IC/3 are used to generate a pulse?

The ultrasonic transducer requires a push pull drive for maximum output.

The transistors are switched so that the pulse voltage across the transducer is is applied one way then reversed.

Note: the transistors are npn and pnp.

 

[ericgibbs]

Look at these twi gif's

Showing the pulse state as High in Red and Low in Green.

 

[legolaslee]

I see! But why can't they just put 1 npn on top, and 1 pnp below, instead of 2 on top and 2 below?

 

[ericgibbs]

I see! But why can't they just put 1 npn on top, and 1 pnp below, instead of 2 on top and 2 below?

How would that reverse the drive to the transducer.?

 

[legolaslee]

Oh. So i have to reverse the drive so the transducer can work. Okay thanks man!

 

[Nigel Goodwin]

Oh. So i have to reverse the drive so the transducer can work. Okay thanks man!

You don't 'have to', but doing so gives you four times the output.

 

[ericgibbs]

The ultrasonic transducer requires a push pull drive for maximum output

hi Nigel,
I did try to explain the push/pull, I think he finally understood.

 

[audioguru]

The CD4093 Nand gates IC is a Schmitt-trigger type.
But the Cmos oscillator should use an ordinary CD4011 Nand gates IC.