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1291  Using Arduino / Motors, Mechanics, and Power / Re: R/C Lawnmower - 2 sets of motors with different gear ratios? on: March 11, 2013, 05:35:28 pm
For the most part I think you'll find your motors will be self-regulating and you shouldn't see this problem. One wheel pushing harder and faster than another wheel should cause that other wheel to speed up/use less current. If your motors have very high gear ratios then yes, you could have a problem, but the easy solution is to just reduce power to those wheels that are running too hard.

The flaw that I see in your design is that you haven't really focused on your main problem which is preventing wheels from losing grip and spinning. You need some kind of feedback from your wheels to see how quickly they are turning so that when one wheel loses grip you can push more power to the other wheels. Traction control, essentially.
1292  Using Arduino / Motors, Mechanics, and Power / Re: Powering pump on: March 11, 2013, 12:14:58 am
http://www.amazon.com/Vdc-Normally-Closed-Solenoid-Valve/dp/B007D1U64E
http://www.allelectronics.com/make-a-store/item/SOL-132/SOLENOID-VALVE/1.html

Have not used one and comments on them vary, but sounds like what you want.  You didn't provide much detail.

If you need a larger valve with well-stated specifications then I would suggest digging through sourcingmap.com. They have a pretty large list of Chinese valves for various voltages / flows / fittings and start around $10/ea.
1293  Using Arduino / General Electronics / Re: Breadboard on: March 10, 2013, 11:58:58 pm
The "ATmega328 on a breadboard (8 MHz internal clock)" thing should be listed in $ARDUINO_HOME/hardware/arduino/boards.txt. I don't know the various versions of the IDE well enough to say if it would be included by default as the tutorial kinda implies, but anyway here's one description on how to add it:

http://arduino.cc/forum/index.php?topic=124879.0
1294  Using Arduino / Project Guidance / Re: construction Laser level for digger on: March 10, 2013, 11:35:57 pm
If you're using a laser + receiver then you want to blink the laser at 38Khz and use three-pin IR receiver module to detect that signal. It's the type of IR receiver that would be used in TV's, etc. with a remote control, but you want a specific subtype that will allow a continuous 38KHz signal. Vishay describes their modules as "fixed gain" in their product matrix. They are really quite simple to use; when the receiver sees the light signal it sets its output pin voltage low and when no signal is present it sets its output pin high.

So on your receiver you need to have a row of X many receivers (~9 or so) to cover the physical distance you want and a way to invert the signal to turn a LED on/off when the laser beam is shining on that corresponding receiver. I believe this is the type of method that is used by the type of laser receiver used in your picture.

On the laser end you need to blink that laser at 38Khz and this can be done with an Arduino or more cheaply with just a 555 timer. Any cheap pen laser will do that without any issue and give you multiple tens of meters of range. A red laser is preferred as that is closest to IR frequency. In your case you need a wide, flat beam and you can find laser pointer modules that will put out a line (I'm sure you've used non-spinning laser levels that cast lines on walls, etc.), but I can't comment on how the reception distance will change in that respect. If the laser line is visible to you then it will be plenty visible to the receiver.
1295  Using Arduino / Sensors / Re: What sensor should I use to detect object going through a hole? on: March 10, 2013, 03:19:55 am
Another benefit of using an IR sensor is that I wouldn't have to worry about changing light conditions, correct? And do I need to do anything special to make an IR sensor work with a red LED?

IR phototransistors/diodes are still plenty sensitive to daylight. They have a pretty wide sensitivity.
1296  Using Arduino / Sensors / Re: peizo knock Example on: March 09, 2013, 04:00:58 am
For cleaning up the signal, try
http://leucos.lstilde.org/wp/2009/06/piezo-transducer-signal-conditioning/
and
http://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/f2012/asj42_gs368_ln226_awh49/asj42_gs368_ln226_awh49/index.html
1297  Using Arduino / Sensors / Re: What sensor should I use to detect object going through a hole? on: March 09, 2013, 01:08:16 am
IR phototransistors are much more responsive (report light changes more quickly) than photocells. If you try to catch a washer free-falling through the hole with a photocell I guarantee you'll have problems -- even using a laser as a light source. Using a real world example I can say that you can pretty lazily drop your arm through the laser and the photocell won't give enough voltage swing for accurate detection.

The simplest solution would be to put a funnel under the hole so the washer ultimately drops through a restricted space. I'd still recommend using an IR phototransistor and a red LED. An IR LED is not required and makes things more difficult because you can't see it. The other advantage of phototransistors is that you can use them with digital inputs and won't have the problems with the Arduino ADC mux.
1298  Using Arduino / Sensors / Re: peizo knock Example on: March 09, 2013, 12:50:40 am
Some piezo buzzers have circuits in them to make them "buzz" when voltage is applied (they're "self oscillating"). That's what yours is, JimboZA, and those (apparently) don't work as knock sensors.
1299  Using Arduino / Sensors / Re: Force Sensitive Resistor sensitivity on: March 09, 2013, 12:40:54 am
The force vs resistance chart for that FSR says it would provide resistance from 30K (20g) to 8K (70g). Using this in a voltage divider as described in the tutorial with the second resistor at 10K and an input voltage of 5V then your resistance is:

10K / (10K + 30K) * 5V = 1.25V (at 20g)
10K / (10K + 8K) * 5V = 2.78V (at 70g)

The Arduino gives 10 bits of precision (1024 values) with its analog readings from 0V to 5V. Between 1.25V and 2.78V (a 1.53V range) that gives you 1.53/x = 5/1024, and solving for x that's 313 values. So, yes, you should be able to adequately identify 20g, 50g, and 70g blocks.
1300  Using Arduino / Sensors / Re: Detecting a high speed object with a phototransistor. on: March 09, 2013, 12:16:05 am
http://www.cameraaxe.com/wiki/index.php?title=Sensors#Projectile_Sensor

Lots of discussion on that projectile sensor if you dig around a bit.
1301  Using Arduino / Project Guidance / Re: Measuring the weight of a beehive on: March 08, 2013, 01:52:11 am
I'm not sure a "balloon" type system would work quite as expected. When weight is added to the hive the balloon will flatten out and result in a non-linear pressure reading at your manometer?

Using the example of a car tire, pressure measured in PSI, the footprint (in square inches) of the tire multiplied by the inflation pressure equals the weight supported by the tire (an "ideal" tire, ignoring sidewall stiffness, etc.). When weight is added the footprint can increase and the pressure can stay near or at the original pressure.

I might be totally off my rocker.

1302  Using Arduino / Motors, Mechanics, and Power / Re: Relay shield on: March 07, 2013, 11:13:16 am
What type of light (voltage / amps / AC or DC)?
1303  Using Arduino / Project Guidance / Re: Load sensor amplifier on: March 07, 2013, 01:01:57 am
I'd be interested in your results, Lefty. Seems too good to be true.
1304  Using Arduino / General Electronics / Re: 109.3035 ohm resistor on: March 05, 2013, 06:34:54 pm
Well, I was implying that if it's spec'd at 109.3035R at 75F then you have to know when it's 75F if you expect it to be at 109.3035R (a circular problem).

As it turns out these types of resistor are accurate to 10 ppm from 15C to 50C so just having it at "room temperature" would be sufficient.
1305  Using Arduino / General Electronics / Re: 109.3035 ohm resistor on: March 05, 2013, 04:13:59 pm
The resistance of a PT100 sensor at 75 degrees Fahrenheit is exactly 109.3035 ohms.

But how do I calibrate my thermometer to 75F?
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