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1  Using Arduino / Sensors / Re: Muscle Sensor v3 problems on: June 12, 2013, 11:25:40 pm
Maybe you are just getting noise.

Does it drop to zero if you short the electrodes?

Have you tried running everything off of batteries w/o a connection to a PC?
2  Using Arduino / Sensors / Re: Ultrasonic HC-SR04 analog output possible? on: June 07, 2013, 11:58:38 pm
Well I was able to get something just connecting to the rear pins of the receiving transducer.

Sampling at 80kHz on a teensy 3.0, while I manually triggered the ping, I was able to see something pretty decent (I think), but it will probably be better to work off my own circuit. Shown is about 8 seconds of data.

3  Using Arduino / Sensors / Ultrasonic HC-SR04 analog output possible? on: June 07, 2013, 03:41:55 pm
I'd like to play around with the raw ultrasonic signal at the receiver of the HC-SR04.

I have found an ultrasonic board to assemble where I could get the analog output, but it cost 10x as much.
The HC-SR04 are so inexpensive it would be great to get the receiver signal before it goes thru some of the other ICs that digitize it.

I can't find a schematic of one, but there's this:,d.cGE

This seems the best doc I've seen for the HC-SR04:

And the SRF04 is similar:,d.cGE&cad=rja

Does anyone have any ideas where to tap in to the circuit to get the analog output of the received signal? Maybe it would be easier if I just use the HC-SR04 for the transmitter, and build a separate receiver to get the analog receive signal. Sound reasonable?
4  Using Arduino / Project Guidance / Re: Arduino with really fast A-to-D on: June 04, 2013, 02:14:02 pm
The teensy 3.0 might be enough.

I can get about 100kHz sampling rate with 16-bit samples, and write to microSD card simultaneously.
I can capture multiple pins but I don't know if it would work for 4. Probably not. I did not write my code very efficiently in places so there's room for improvement.

If I could do the sampling with DMA (I think others have) it would probably be able to do much more.
5  Using Arduino / Project Guidance / Re: Teensy 3.0 help. on: June 04, 2013, 02:00:21 pm
I've enjoyed working with the teensy 3.0. It's been much easier for me to work with than my efforts in the past with a Mega. And it's power and capabilities are not wasted due to the creator's efforts.

I have been soured on shields, because unless you are you using the most common arduino flavor at the moment, you have to try and figure out the exceptions.
For me, it seems a better use of time is just figuring out how to wire things up yourself, rather than trying to work around a shield that tries to optimize it for one specific board, and all other boards have to try and figure out how to work around it. Ultimately, there's a simple fix but figuring that out can be trying. I had cases where it was documented that I would need to wire things up differently (and/or bridge a pad) to the shield, but then the library would do an ifdef on the board, and cause pins to be used differently, and that caused a lot of headache with all the re-direction.
6  Using Arduino / Project Guidance / Re: Buying an affordable EEG device on: May 28, 2013, 05:25:21 pm
The TI chip is the way to go. I have a sample, but haven't spent the time yet to solder it onto a board.
I've seen the EEG off of someone else's device though and the EEG was beautiful.

And, I would never hook an electrode to anyone without everything solely running on batteries, and no electrical connection to anything else.
I choose to protect me from myself. smiley
7  Using Arduino / Sensors / Re: EMG delsys on: May 22, 2013, 12:13:23 pm
It can be amplified at the electrode or at the end of the wire, but in any case it needs to be amplified. I imagine the delsys amplifies the signal for you at the source. From the electrode on the skin, you are getting about +-100 microvolt signals, so this is a challenging aspect. With movement, you will get artifact from movement alone.

Also, you will get muscle firing from just tense muscles, which doesn't necessarily imply movement, and if there was movement you wouldn't know what kind of movement.
8  Using Arduino / Sensors / Re: EMG delsys on: May 21, 2013, 05:13:21 pm
surface EMG (sEMG), you are going to get very gross information about many muscles.

Needle electrodes (ouch) can gain more specific information, but even that has a lot of contamination from other muscles.
9  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: March 05, 2013, 10:06:23 am
OK, I'll do that. But I'd like to figure out why this circuit is not behaving like I expect. It bugs me that I can't even get 1.25 volts that this IC is supposed to maintain across those 2 pins. I'd like to see if I could get something like 1 mA or something from it.
If someone can tell me that the breadboard looks OK that would be very helpful. At least I would know if I'm understanding the circuit diagrams. Thanks for any help. I think I'll go read some of the general electronics post and see if I can feel comfortable with other circuits and their discussions.
10  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: March 05, 2013, 03:27:50 am
Didn't realize the thread was continuing. I have been busy reading some books and trying to understand electrical circuits and how to do the current source.

I'm working with an LM317T, but I'm having trouble with the basics. I thought I understood what was going on, but I don't.
V=IR, so since the IC is maintaining 1.25 volts across the "output" and "adjust" pins, I can use a 12.5kOhm resistor.

Oddly, I never get a 1.25V reading across the output and adjust pins.  Obviously I'm missing something.
If anyone wants to take a look, this is my understanding of the circuit diagram that I'm trying to duplicate in the breadboard. Attached pdf.

But I am having many difficulties with the basics. The voltages at the output and adjust seem to be zero, with both being about a 0.5 volts less than the input with reference to ground.

I am also having difficulty measuring current. I setup an LED so that I make sure that the current was flowing thru the multimeter, but when I connect the multimeter in series the LED goes off.
My multimeter is very confusing in regard to units of current (uA/mA/A), and seems unstable. But that's probably cause I'm doing something wrong if I can't get current to go through it.

And when I plug the circuit into a higher voltage power source (2.5V, 3.3V) the LED gets brighter, which would seem to indicate more current and thus not working as a constant current source. As I think LEDs get brighter on current and not voltage. When I plug in a 5V power source it starts fading and getting erratic so I guess that voltage is nearly out of range for the LED.

I did manage to get IC fairly warm when I plugged stuff together in certain ways so I assume it does work.

Oh, and yes at some point I can calibrate the sensor. But I still likely need a constant current source so that the calibrations don't change over time.
11  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: March 01, 2013, 01:06:55 pm
Don't trimpots usually have much higher tolerances and produce noisier signals?
12  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: March 01, 2013, 02:06:48 am
The signal is looking better with a better resistor for the instrumentation amplifier. I used a 10.2kOhm/0.1% tolerance. I attached a pdf of the pressure signals again.

The pictures are from 2 different trials.
Oddly, it does seem the device is altering the pressure a bit when it is detecting the systolic & diastolic blood pressure. Cause some noise-like signal appears where those pressures are in each trial.
13  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: February 28, 2013, 03:51:25 pm
You're right, I worded it wrong.

I meant the opposite. The good resistor I have is 0.05%, and the other one I'm using I don't know. But I'm guessing probably 5 or 10%.
14  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: February 28, 2013, 03:06:51 pm
I think part of my noise problem is the resistor I'm using now for the instrumentation amplifier.

I don't know the tolerances on the one I have but it's probably not good. The one I was expecting to use, until it was apparent the output of the sensor was 10x what the datasheet said, was very good. Now I'll just need to find one with better tolerances.

I hooked up the resistor with lower tolerances and the signal looks pretty clean with me just blowing pressure in the tube to the sensor.
15  Using Arduino / Sensors / Re: Problem with amplifying a pressure sensor for measuring blood pressure on: February 27, 2013, 12:18:26 pm
I'm sure you're right that I won't comprehend it, but I can get some assistance from others who do. So I'll look into it.

I do see this which may be what you were talking about:
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