Ultrasonic circuit explination

[Corky]

I know this is a very common circuit to build as a beginner but i cant get my head around it, this is my undertsnading so far:
the ultra sonic transmitter and reciever work as an object detection device, when the reciever is activated the small voltage travels to the 3 op amps and gets amplified to make the led come on which in turn makes the relay switch on, but i am having trouble with the need for the 555 timer, i have simulated this circuit and i still cant understand what it does, i understand the normal operation of a 555 timer which has possibly confused me more.
any advice or infomation on this would be much appreciated

Dale

 

[ericgibbs]

hi Dale,
This circuit appeared on another forum site, its totally useless and will not work as described or as drawn.
Trying to contact the 'designer' [I use that term loosely] is a waste of time. no response.!

Eric

 

[JimB]

The 555 is an oscillator driving the two transistors which form a basic amplifier to drive the ultrasonic transmitter.

Having said that, there are several things about that circuit which make me think that it was drawn by someone who does not know what he is doing.

JimB

 

[JimB]

EG, good to see that we are in agreement on that circuit!
JimB

 

[Corky]

thanks guys, i was having doubts myself, i had simulated this circuit and couldnt get it to work how i was expecting to too, back to the drawing board again i think

why would he need an amplifier to drive the transmitter?

 

[ericgibbs]

thanks guys, i was having doubts myself, i had simulated this circuit and couldnt get it to work how i was expecting to too, back to the drawing board again i think
why would he need an amplifier to drive the transmitter?

Hi,
This is a good question, he does not specify the types of ultrasonic TX or RX sensors, a high power TX would require a buffer amp.
He does not specify the LED, LDR Relay etc.....
The 9V batteries with this design would have very short life, also WHY is isolation needed to drive a relay.?

Eric
I have some LTSpice sims I did for anther OP trying to build this circuit, if you are interested.?

 

[JimB]

why would he need an amplifier to drive the transmitter?

To give it more Oooomph!

More seriously, the characteristics of the ultrasonic transmitter are unknown.
It may need more power to drive it effectively than can be provided by the output of a 555, especially a low power cmos version (7555) used in that circuit.

JimB

 

[Corky]

ive done a bit of research and found the reason for the 555 which i wasnt understanding, its to create the needed 40KHz which is now obvious,

I dont have LTSpice i use livewire for my projects, i havent used LTSpice so i dont know much about it. would you reccomend it? and do you know where i could get it from?

 

[ericgibbs]

hi,
Look at these images, I will post a link for LTSpice, which is free, also a free Yahoo user group.

This RC amp uses CA3240 OPA's.
E
https://www.linear.com/designtools/software/?gclid=CPWsppLZl8ECFc7HtAodVn4AXg#LTspice

https://groups.yahoo.com/neo/groups.../neo/groups/LTspice/files/%20Lib?prop=eupdate

 

[Corky]

these drawings are really helpfull and im getting there but im still unsure what the transistor pair section is doing, i have simulated again on this drawing and i can only see it inverts the output, am i right in thinking that and if so why would this be needed? thanks again

 

[ericgibbs]

The transistors on the 555 output are supposed to be a push pull arrangement that could deliver more 'power' to the transducer than a 555 can supply.
The same circuit could use a 7555 which is CMOS version and has a lower drive capability than the 555 TTL version.

Again , not knowing details of the users TX transducer.?
E

 

[Corky]

I have simulated this, it shows on the simulation that the 555's output is 9vish and when i use the 'boxed section' it only inverts the output.

i am confused about why this would be needed?

 

[ericgibbs]

i am confused about why this would be needed?

hi dale,
My last post explains it.
Look and compare these two images, 555 and 7555, also tell what are drive requirements of TX transducer.?
Also on your sim compare the power level at the transducer with and without the buffer.

 

[ericgibbs]

I should also point out the loading of the transducer on the output will also effect the 40KHz 555 frequency setting, as we dont know the transducer spec', the transistor buffer also isolates the transducer from pin #3.

EDIT:
Compare the two version, buffer, no buffer.
I have had to adjust the timing on the unbuffered version to get the frequency back to 40KHz, also note now the Mark/Space ration is no longer 1:1.

Also observe the power difference in the 470 load, the difference increases as the load resistor value is reduced.

 

[audioguru]

I wonder why the receiver transducer is connected directly to the 9V battery and ground?
If it is not connected to +9V then positive going input halfwaves turn on non-inverting opamp A which turns on non-inverting opamp B which turns off opamp C which turns off the LED.

EDIT: I forgot to say that 3 opamps are used in the receiving amplifier because the lousy old LM324 opamps have hardly any voltage gain at 40kHz.

 

[chemelec]

Not Only is the 40 Khz Reciever at 9 Volts, So is the input at Pin 3 of the LM324.
Obviously this won't work as shown.

 

[Corky]

eric gibbs, your posts have helped me out alot, thanks alot

ill give it a go making it myself from scratch now its gonna be better for me to learn aswell

ill let you know if i get any problems lol

Dale

 

[Corky]

would it be better to not have a load resistor?

 

[audioguru]

would it be better to not have a load resistor?

The load resistor represents the load caused by the transmitter transducer that we know nothing about.

 

[chemelec]

Looking over that Schematic, There are Many Errors.

I'm considering to debug it and draw up a new, working schematic for it.
But not much time now as I am going for a holiday to Australia in another week from now.