Ok, it has a mistake in my digramm, when the Rx receive an echo wave, the reset of comparator is at 0V, so the output of comparator still be at 0V everytime

humm how can I correct this without another logic gates ?

 

finaly, i think that my last diagramm is ok

When we generate the ultrasonic wave, Input of the 0,5ms multivibrator will be at 5V, and the reset of comparator will be at 0V during 0,5ms
If we have a received wave during the 0,5ms, comparator will stay at 0V

Now, after 0,5ms, reset of comparator will be at 5V, if we dont receive any echoes, output of comparator will be at 0V, and the 0,33ms multivibrator output will be at 0V, we must wait 1 second to generate the next wave.

But if we have an echos, the output of comparator will be at 5V, and this wil be trigger the 0,33ms monostable, and immidiatly sent a second wave and in the same time, the 0,5ms output will be at 0V, and output comparator will be at 0V with or without echoes (during 0,5ms)
etc etc
If my diagramm is ok, can you help me to choose the best compoents to do this


NE 555 : 1Hz, 3KHz and 40 KHz generator
0,5ms : multivibrator with Q/Q_ output two gate of 4093 ?
Ampli : ???
Comparator ???
MOSfet : IRF 630 N channel
Diodes : 1N4148

 

what is aop? I would simply use AND gate after the output of the comparator.

 

Or, since a comparator will be open collector anyway, you can use a transistor to ground the ouptut of the comparator.
But still, I am not so sure that a comparator will detect the signal correctly, it might trigger for just about any noise that gets into the rx. I think the lm567 will work better, and it has open collector too so you can switch to it in the process.

Anyway this seems so simple that I am tempted to build it myself too.

 

Ok, here a 567 is used to detec the (only) 40KHz ultrasound wave
http://basicrobot.blogspot.com/2009/03/ultrasonic-sensor-circuit-1.html
(see the last schematic)
But, author use also a comparator (the LM311) " To help minimize false
triggering, the output is fed into a voltage comparator set to trigger
at the appropriate level."

So , it's possible to use the receiver stage of this schematic, and add the transmitter stage of my schématic

 

ok and now what do you think ?

 

hum sorry, but it's no problem with the output of the 567 decoder, as the output of comparator is at 5V when we have an eco an at 0V if not
But where is the restet pin of 567 ?
http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS006975.PDF
It's the Pin 4 ???

 

can this be a definive diagramm ?

sound frequency is 125Hz (at 136cm) to 1724Hz (at 10cm)

 

Pin 4 is definitely a supply voltage. You should feed the monostable output through a resistor to the base of npn transistor, which will switch pin 8 to ground.

 

like this ?

 

definitive electric schematic ?
Any reccomandation ? any idea to eliminate few components ?

 

yes that´s it.

 

Personally I find that project (the link in the first post) to be terribly annoying, and offensive to Leon Theremin and anyone who has seen an actual theremin in operation. However, since it is what you have asked for, I suppose I have no choice

I stumbled across this simple version of the instrument that sounds a little more like the original, and requires similar movements. It doesn't require ultrasonic rangefinders (which really ought to have a microcontroller to decode the inputs). All it needs is a pair of 555 timers and a couple of LDRs:

I realize this might not be what you're looking for, but I wanted to throw it out there just in case.

Good luck!
Regards,
Der Strom

 

It doesn't require ultrasonic rangefinders (which really ought to have a microcontroller to decode the inputs).

µcontroller is not a neccesity, there's a lot of ultrasinc project without controller

Two CDS photocell ? why ???

 

µcontroller is not a neccesity, there's a lot of ultrasinc project without controller

Two CDS photocell ? why ???

a microcontroller makes decoding the signals much easier, but that is true--it's not absolutely necessary.

The photocells respond to the change in light (shadows) created by the hand. The closer your hand gets to the LDR, the darker it gets. It preserves some of the original idea behind the real theremin.

 

Hello,

There are a lot of theremin schematics around:
http://www.thereminworld.com/schematics

Most of the schematics make use of RF generators.

Bertus