Ultrasonic Receiver Circuit at 25kHz

[killer_fighting]

http://www.ecelab.com/circuit-ultrasonic-r.htm

Above is the circuit that I found from ecelab. The receiver circuit is meant to receive 40kHz. But, I need to receive 25 kHz signal instead of 40 kHz. Can I know how should I scale down my resistor, capacitor and voltage value?

 

[Nigel Goodwin]

The only changes needed are to alter the PLL frequency (check the dataset for the formula) and to use a correct ultrasonic receiver - do you have a 25KHz transducer?, it's a fairly obscure value (and barely ultrasonic).

 

[duffy]

^ Yes, nearly all of those those transducers are resonant. They don't work like a microphone, which can pick up a range of frequencies - most of them are tuned to receive and transmit on one particular frequency.

Notable exceptions are the Knowles SPM0404UD5 and the Senscomp transducers.

 

[canadaelk]

As duffy points out: these transducers are tuned to that 40kHz. Therefore, if you use a standard mic capsule, you will need a very narrow (high Q and gain) filter to cut off anything below and above the proposed 25kHz. Breadboarding will n ot do. A pcb with ground-plane is needed (that was my experience). E

 

[killer_fighting]

The only changes needed are to alter the PLL frequency (check the dataset for the formula) and to use a correct ultrasonic receiver - do you have a 25KHz transducer?, it's a fairly obscure value (and barely ultrasonic).

Yes, I have a pair of 25kHz transducer. Sorry, may I know what do you mean by PLL frequency? Which dataset that you mean?

 

[killer_fighting]

As duffy points out: these transducers are tuned to that 40kHz. Therefore, if you use a standard mic capsule, you will need a very narrow (high Q and gain) filter to cut off anything below and above the proposed 25kHz. Breadboarding will n ot do. A pcb with ground-plane is needed (that was my experience). E

How can I calculate the high Q and gain?

 

[ronsimpson]

Look at the data sheet for the NE567.
There is a formula for the frequency F=1/1.1RC That is the RC on pin 6.
There is also a formula for Q or bandwidth.

 

[audioguru]

It is a horrible circuit:

The lousy old 741 opamps have trouble above 9kHz.
The second opamp has no negative feedback so its output will be full of low frequency noise.
Resistor R5 is doing nothing and can be replaced by a piece of wire.
The 9V battery is missing a bypass capacitor.

 

[killer_fighting]

I see. In my ultrasonic circuit, I am actually ignore the NE567 part. To build the complete ultrasonic circuit, I have to include the NE567 part? Otherwise, do you guys have any suggested schematic diagram for me? I need an ultrasonic receiver circuit at 25 kHz.

 

[Nigel Goodwin]

I see. In my ultrasonic circuit, I am actually ignore the NE567 part. To build the complete ultrasonic circuit, I have to include the NE567 part? Otherwise, do you guys have any suggested schematic diagram for me? I need an ultrasonic receiver circuit at 25 kHz.

What exactly are you trying to do with it?. The NE567 is a PLL, and detects the 25KHz.

 

[audioguru]

The horrible amplifier will amplify all sound frequencies, not just 25kHz. Your 25kHz transducer might pick up a lot of background sounds. The NE567 is a circuit tuned to 25kHz and it is not affected by other frequencies.

What do you have that produces 25kHz? One of the transducers?

 

[killer_fighting]

What exactly are you trying to do with it?. The NE567 is a PLL, and detects the 25KHz.

I will explain it in details. Before that, let me shows the images for both of my ultrasonic transmitter and receiver which I bought from maplin.co.uk.
Ultrasonic Transmitter (25 kHz)
View attachment 61484
Ultrasonic Receiver (25 kHz)
View attachment 61484

I am doing a project which is related about communication part. I will use a microcontroller chip which is PIC16F648A to produce an input signal (25 kHz) with the function of CCP1 (PWM) in the PIC16F648A. In my planning, I will connect the Ultrasonic Transmitter to the inverting input (refer to LM741). After that, I will connect the Ultrasonic Receiver to the output (refer to LM741). Hence, the receiver must be able to detect the input signal 25 kHz which later on will be produced from ultrasonic transmitter.
Before I can do that, I must build an ultrasonic receiver circuit. Hence, I am eager to get a suitable and correct schematic diagram.

 

[Nigel Goodwin]

Sorry but you're still not explaining anything?, what is your end project supposed to do (not how you think it needs to work).

There's also no need to bother with the PWM module to transmit 25KHz, it's easier (and more versatile) to do it with simple timing loops.

 

[audioguru]

Maplin does not say who made the transducers and do not have detailed datasheets, so they are garbage.

 

[Sceadwian]

AG, could you be a little more negative? I have transducers just like this, they're simple and dirt cheap, it's nothing more than a piezo element connected to a small diaphragm, they work just fine as long as you don't expect epic range or power.

Seeing as how this is your project what have you done to create your own schematic Killer, there is more than enough available schematics that can be easily altered to suit your needs if you put forth the effort.

 

[canadaelk]

Sceadwian: My Lord, AG has tried. At times he even succeeds! E

 

[duffy]

OP - change that .01μf cap to a .015μf cap.

The equation you need for the center frequency of the 567 is

[LATEX]f_0 &= \frac{1}{1.07*R_8*C_5}[/LATEX]

Figure the center of the 5k pot is 2.5k, right? So plug in 2500 for R8 and .000000015 for C5 and you get:

[LATEX]f_0 &= 24.9khz[/LATEX]

You can adjust that to exactly 25khz by trimming the pot to 2492Ω (but it isn't that critical). The rest of the circuit will work at 25khz or 40khz - the only other frequency issue would be the transducer itself, and you say you have one resonant at 25khz.

 

[killer_fighting]

OP - change that .01μf cap to a .015μf cap.

The equation you need for the center frequency of the 567 is

[LATEX]f_0 &= \frac{1}{1.07*R_8*C_5}[/LATEX]

Figure the center of the 5k pot is 2.5k, right? So plug in 2500 for R8 and .000000015 for C5 and you get:

[LATEX]f_0 &= 24.9khz[/LATEX]

You can adjust that to exactly 25khz by trimming the pot to 2492Ω (but it isn't that critical). The rest of the circuit will work at 25khz or 40khz - the only other frequency issue would be the transducer itself, and you say you have one resonant at 25khz.

Cool, thanks for your explanation. By the way, I got a doubt, for my ultrasonic receiver circuit, does it is compulsory for me to include the NE567? What is NE567 used for? The values that I need to change is OP, R8 and C5, right?

Thanks for your details explanation!

 

[duffy]

YOU are OP - Original Poster. This is slang for the person who started the thread in a discussion on the internet.

R8 and C5 are on the NE567.

The NE567 is a PLL - Phase Locked Loop. It "locks phase" with an input frequency. This is the part that actually detects the 25khz frequency. If you want to detect 25khz, you need this part. The "decoded output" turns ON at 25khz. It is OFF at 26khz, or 24khz or any other frequency.

Unfortunately, ON and OFF are a transistor connected to ground, so you must provide a "pull up" resistor to read it, and when it is ON the output will be 0V and when it is OFF the output will be at Vcc, which may seem backwards, but is helpful if you are connecting a microprocessor that operates at a different voltage. Look at figure 16 and 17 on this page: **broken link removed**

The other parts of the circuit are an amplifier and a comparator, they will work at many frequencies. U1 is the amplifier. U2 is the comparator - this makes square waves, all the same amplitude (about 7.5V) out of the sine waves from the amplifier before sending them to the PLL.

In post #1 you said you wanted to "receive 25 kHz signal instead of 40 kHz". That frequency detection is done by the NE567. I did not understand your explanation in post #12. It would help if you drew a schematic (even a pencil sketch) of what you want to do.

 

[killer_fighting]

YOU are OP - Original Poster. This is slang for the person who started the thread in a discussion on the internet.

R8 and C5 are on the NE567.

The NE567 is a PLL - Phase Locked Loop. It "locks phase" with an input frequency. This is the thing that actually detects the 25khz frequency. The other parts are just an amplifier, and a comparator. U1 is the amplifier. U2 is the comparator - this makes square waves, all the same amplitude (about 7.5V) out of the sine waves from the amplifier.

In post #1 you said you wanted to "receive 25 kHz signal instead of 40 kHz". That frequency detection is done by the NE567.

I did not understand your explanation in post #12. It would help if you drew a schematic (even a pencil sketch) of what you want to do.

Where should I connect my ultrasonic receiver? Connect at the pin 2 from U1? I will scan my schematic and post to here tomorrow as I don't have scanner at here.