Indeed I was confused, Thank you very much for the simplification of the concept. I noticed that the reactance of the capacitor and inductor values was both close to +30k and -30k, which makes sense now why you asked for that value.

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/signals/complex/react.html

I changed C1 to 22pf and inductor to 22.2, the circuit is so much better tuned now, I get a good signal with a 30k resistor and I use much less current (15 times less?) My transducer voltage went up significantly too, given the smaller current drawn.

My next step....

I like to try and clamp that source (TX) down to ground. I have a 100 transistor pack and both a NTE2361 (NPN) SI NPN HI speed switch and a NTE2362 (PNP). As I mentioned I'm not as good on transistors, re-learning my way though. Any help on figuring out those values?

dc42,

Here is my current circuit...



I some calculations and came up with:

fc= 1/(2*pi*sqrt(1mH * 670pf)) = 194.438KHz

Not sure how to apply the 4pf capacitance from the diodes, which may or not make a difference.

Here are some results...

R1 = 30k



R1 = 5.6k



R1 = 2K



I have a small assortment of transistors (I'm not as good on transistors) my experience has being that they were too slow on RF level, likely because of the saturation you mentioned. I'm looking for a signal mosfet for that clamping of the Tx but in the meantime, how would I go about the transistor amplification? Given that I'm short on a high BW op-amp.

pito,

Good points on resistive loading on my transducer, the datasheet on the transducer says 60 +j0(t) (uses internal transformer) 500 watts, so it does not seem to hurt it so far.

http://www.odomhydrographic.com/media/user/file/AirmarTransducers/ss510_rD_lr.pdf

I'm currently using a 10nf in series with a 2k resistor. I also use a 1mH inductor in parallel with the diodes, which gives me a great looking signal atm. (I'll soon post a screenshot of my scope)

You are correct about the 328p, the fastest I can sample with the Uno is around 16-20us, way slower than what I need. I will however try and use the Due tomorrow (I got two with me).

The current application for this is an echosounder, just for depth which I feel I can accomplish with just timing but I rather digitize the signal and do some DSP with it for future projects of underwater acoustics. Seems like 4us sampling (250KHz) is the best I can accomplish with the Due, from reading this:

http://www.djerickson.com/arduino/

Seems I'm close now to getting this into the Due, if it could do 500KHz (apparently stated in the datasheet) I would be golden...

I'll also look into that higher BW op-amp, Thanks!

Thanks for all the replies!

The dual diodes trick certainly got me started! I tried that spice circuit and as dc42 mentions, I used the 102 capacitor, replaced the 100k resistor with a much smaller one and got better results, also used a 1mH inductor to dissipate the DC build up, the end result so far is a really short blanking area of <100us (way better than I expected).

As dc42 also mentions, the bandwidth limitations of the LM324 would not allow me to even make a unity gain filter.
I now realize I need much better bandwidth op-amps. What would you guys suggest?

My transmit pulse is about 100 us, this signal returns after a short period (a couple hundred microseconds) so there is no overlapping between transmit and receive, both are 200 KHz. I would like to transform the return signal up to 0 to 5v, currently it is a couple hundred millivolts on the best case.

I'm building a water echosounder with a single transducer (200 KHz). All works well on the transmit side, but now I want to read the small signal returning. My transmit is in the hundreds of volts (about 600-800 vpp) and the signal I'm interested in is in the millivolts. From the end of the transmission to the start of receiver could be as low as 150 us.

My problem is that I can't figure out a way to hook up this to a microcontroller without burning it. How could I extract the smaller signal ?

@Crossroads

That SRAM chip might just do it for me!

After I get some SRAM, I could just do some simple code to read and write over SPI as fast as possible for say 5ms and see how many times it does it. I wonder how you guys manipulate the sampling rate of the Arduino's ADC? If this even helps...?

Thank you all for the information provided!

I have to say I will need to attack this on a different approach than I initially intended. This is what I'm trying to do...

A signal comes in, which will be between 0V and 5V. The signal is between 1ms and 5ms long. I would be sampling this as fast as possible, storing the values and later sending them over a wireless serial radio. So the main thing then would be a way to store as many samples as possible during that short amount of time. If the Arduino could simply store those samples in it's memory then great! But I think it is beyond it's memory capacity, but I could use external EEPROM to store the information and send it after the signal has finished. How fast could I sample then if I don't have to worry about the baud rate, only storing on EEPROM ?

I see you guys mention how fast the ADC on the Arduino samples, I was not aware that you could manipulate the sampling rate of the ADC on the Arduino, any light on this?
I also like the idea of a faster baurdrate to help do most of this on a real time basis, I might end up doing this on a separate project for signal detection.

I'm currently trying to use the Arduino's ADC to sample a waveform that will be between 0V-5V and transmit the samples over serial so that it can be recreated on a PC running some plotting software. I would like to know how fast can I sample a waveform (1ms? 1us?) and be able if possible, to transmit this data real time. Another option would be to store about 8 seconds worth of sampling and transmitting such samples. How fast could I sample? I'm willing to use the fastest baud-rate possible to achieve this and if there is a better option than using the Arduino.

I could also use many Arduinos to do it too.

Sounds very easy!

I'm in fact going to be in Houma, La Monday

I actually got some of those Push buttons laying around, a HD Brushless DC motor and a steeper controller I could put together in some sort of way.

PM me some info

You will need to enlighten me because I'm lost here.

What is Pin 17 for? I have done both the sensing EMF from all 3 phases with a 10k resistor and also using the 4'th connector on the brushless DC motor on which cases it both uses sensing to decide the next step against it's internal EMF comparators. How is this none sensing?

Did you look at the data-sheet I posted?

Pin 1, 3 and 16 run the 3 phase and pin 17 does the sensing. Pin 4 can be used to control the outputs, Check Page 11.

[Serial]

while(Serial.available()>0)   
{
  int incomingserial = Serial.read();
  if(incomingserial == a)
  {         
    while(sensorread==LOW)
    {
      Serial.print("This Is Case A");
      digitalWrite(motor1, HIGH);
      delay(500);
      digitalWrite(motor1, LOW);
      digitalWrite(transmitter, HIGH);
      digitalWrite(buzzer1, HIGH);
      sensorread=digitalRead(pinx);
    }
  }
}

The way I wrote it, the while statement will run indefinitely until sensorread becomes HIGH. Could you post your entire code?

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1251570417

Would be a good start...

Why not use this?

http://www.nxp.com/documents/data_sheet/TDA5140A.pdf

Works for me...