• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Amplifying a 2.5V Square wave coming from a microcontroller?

Status
Not open for further replies.

sarahtelayrii

New Member
Hi,

I'm just asking for some assistance since I'm not sure of amplifiers much.

My question is that I've programmed my PIC micro that is emitting a Square wave 2.5V peak to peak to a transducer that can handle up to 140V, the thing is that I need to amplify this signal to at least 10 times so it's 25V peak to peak if possible at the output?? A overall gain of 10 times or higher.

I'm stuck between choosing between a opamp? voltage comparator? to amplify the voltage? I'm good in programming micros and electric circuits but when it comes to electronics part ive been somewhat confused in the amplifiers area. Also I checked my uni books however it explains only theory and there's no mention of any practical application (there's only info on sine waves, not square waves) that meets my need.

I have a 9V rail as well if need be. So any push in the right direction would be loved! thanks...
 
Last edited:

Hero999

Banned
You don't need an a linear amplifier like an op-amp.

You just need a switch.

You haven't told us anything abou the transducer: does it require a push-pull driver or will single ended do?
 

MikeMl

Well-Known Member
Most Helpful Member
Also, unless you can use a transformer or inductor, you will need a power supply voltage of at least 25V or higher. Do you have that available?
 

sarahtelayrii

New Member
A switch? :confused:

I've seen example circuits but they don't seem to make much sense and I'm not sure if they can give the output I'm looking for.

BTW its an ultrasonic transducer working from 38-40KHz.
 

sarahtelayrii

New Member
ahh the whole project runs of a 9V battery...

the micro takes in 5V and provides that 2.5V to the ultrasonic transducer. Instead of 2.5V I need it amplified. If not 25V but as much as possible..?

However I can get the 9V battery into a parallel configuration and yes now I have a 9V rail available...
 

MikeMl

Well-Known Member
Most Helpful Member
Any idea what the impedance of the transducer is?
Do you know if the transducer can tolerate a DC offset?
Do you have a link to the data sheet for the transducer?

If all you have is a 9V source, then all you can easily do is drive the transducer with a 0-9V squarewave, which obviously has a DC component. If the transducer cannot tolerate the DC offset, then you can Capacitively couple the transducer, in which case the transducer will get a -4.5V to +4.5V squarewave.

If you need more than 9Vp-p, then as I said earlier, you will have to use a transformer with step-up windings which will simultaneously boost the voltage and eliminate the DC component, or you will have to provide a higher voltage battery.
 

crutschow

Well-Known Member
Most Helpful Member
If you need more than 9Vp-p, then as I said earlier, you will have to use a transformer with step-up windings which will simultaneously boost the voltage and eliminate the DC component, or you will have to provide a higher voltage battery.
You should couple the source signal through a capacitor into the transformer to eliminate any dc into the transformer as well. Otherwise there will be a dc current component out of the source which will tend to saturate the transformer.
 

Hero999

Banned
ahh the whole project runs of a 9V battery...

the micro takes in 5V and provides that 2.5V to the ultrasonic transducer. Instead of 2.5V I need it amplified. If not 25V but as much as possible..?

However I can get the 9V battery into a parallel configuration and yes now I have a 9V rail available...
How much power do you require?

If it exceeds a couple of Watts then it isn't practical to run the thing off a single 9V battery.
 

Mr RB

Well-Known Member
Try a h-bridge IC, run from the battery you will get 18v peak to peak. Most of the little h-bridge chips will take a logic level input and drive 9v supply no problems.
 

sarahtelayrii

New Member
its a normal ultrasonic transducer...here's the data sheet:
http://www.electro-tech-online.com/custompdfs/2009/05/AU5550.pdf

I have it generating 38KHz square wave just fine, the transducer can even handle bandwidth greater than 150KHz as tested via uni lab equipment.

I just want a detection range of about 2-3 meters....mine so far can detect about 20cm without any amplification...

so the idea is the echoes come back and I can determine its distance. On the receive circuit I have plans for an inverter to amplify whatever is coming back to 5V peak to peak and then use a schmitt trigger to smooth it out into a square wave as much as possible.

I plan on using the 74HC14 Hex schmitt trigger inverter.
 
Last edited:

MikeMl

Well-Known Member
Most Helpful Member
First, it looks to me that is intended to be driven a 40kHz+-1kHz, which suggests that it is a self-resonant device. Shouldn't be hard to rewrite your code to move the excitation freq from 38kHz to 40kHz. If it is resonant, it might be a high Q device, so it will have greater output and receive sensitivity at its natural resonant frequency.

Second, this topic has come up before on these forums.

Can you use two port pins and drive them with opposite polarity. Driving the transducer differentially would double the drive amplitude per Mr RB's suggestion?
 
Last edited:

sarahtelayrii

New Member
I checked with both 38KHz and 40KHz there's not much different in terms of detection in cms. It's on 40.04KHz right now anyway. If I place a flat book on top the sound reflects but to a noticable extent about 20cm away regardless which is picked up by the receiver.

Anything further distance than 20cm the transmitter doesn't send the ultrasonic waves far enough. I want it at around 2 meters at least but with reasonable accuracy. The appropriate sensitivity of the tx/rx transducers is 40KHz.

Would a LM311 be enough for this? That is as its input a 5V p-p?

And PSPICE isn't seeming to be much help, if I use an opamp in an non-inverting or inverting amplifier configuration the output is *always* 15V or -15V (due to polarity change) regardless the input is at 1V or the resistors are changed in an attempt to change the gain to affect the output.

PS: I checked out that link, the guy was trying to use the same device im using to act as both a receive and transmit. But im using a separate device for receive so it would be different...
 
Last edited:

ericgibbs

Well-Known Member
Most Helpful Member
Would a LM311 be enough for this? That is as its input a 5V p-p?

And PSPICE isn't seeming to be much help, if I use an opamp in an non-inverting or inverting amplifier configuration the output is *always* 15V or -15V (due to polarity change) regardless the input is at 1V or the resistors are changed in an attempt to change the gain to affect the output.
hi,
Post the Spice *.asc file for the OPA cct, the LM311 is a comparator not a OPA.?
 

sarahtelayrii

New Member
Hi, here it is, a amplifying circuit using opamps. It's supposed to have a gain of 10 but the output doesn't reflect having a gain of 10 via an input of 3V. It's always 15V output, regardless of the resistor values or the input voltage:

 

Sceadwian

Banned
Are you powering the opamp via a +/- 15 volts? Cause 10 times -3 is -30, your opamp is saturated at the negative rail. Also the opamp is dead shorted, if you want to be able to read a voltage properly at the output you'll have to put a resistor to ground, try 1k ohm.
 
Last edited:

MikeMl

Well-Known Member
Most Helpful Member
Why is output of the op-amp grounded?
 

MikeMl

Well-Known Member
Most Helpful Member
Here is the correct way to set up a Gain of 10 amplifier:

Note the offset between Out1 and Out2. If using an opamp (instead of a comparitor), no resistive pull-up, pull-down, or resistor to ground is need to load the opamp.
 

Attachments

Last edited:

Sceadwian

Banned
Which still won't work at an input of 3 volts as it's past the power rails.
 

MikeMl

Well-Known Member
Most Helpful Member

Attachments

Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top