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46  Using Arduino / Sensors / Re: LuminOx oxygen sensor on: February 13, 2013, 07:34:16 pm
You can use the 5V pin of the Arduino to power the sensor.
The term "3.3V TTL level RS232" indicates that the serial connection is with digital signals of 3.3V.
The Arduino Uno uses 5V digital signals, so you have to adapt them to 3.3V.

The conversion of RS232 5V to 3.3V is not hard to do, I can't find it right now. Hopefully someone else knows.

The serial port is used to upload a sketch and for the serial monitor.
But if you use SoftwareSerial, you can create a second serial port for the sensor.
http://arduino.cc/en/Reference/SoftwareSerial
That way, you can still send messages to the computer, and have full control over the sensor.
47  Using Arduino / Networking, Protocols, and Devices / Re: /dev/ttyACM0 in bash on: February 13, 2013, 02:28:01 pm
You could set the settings for the serial port, with stty
48  Using Arduino / Project Guidance / Re: New to this. Need advice with USB mouse interface on: February 13, 2013, 12:58:18 pm
That is very interesting, but I can't open the Eagle schematics file.
Is the page more useful : http://fab.cba.mit.edu/classes/4.140/people/andy.bardagjy/input/index.html ?
The datasheet provides also example schematics : http://www.avagotech.com/pages/en/navigation_interface_devices/navigation_sensors/laserstream/adns-9500/
But it seems rather difficult.
49  Using Arduino / Project Guidance / Re: Lamp controller on: February 13, 2013, 08:11:30 am
It can be done.
The Arduino Mega 2560 has more serial ports, and the SoftwareSerial can create serial ports on normal pins on the Arduino Uno.
http://arduino.cc/en/Main/arduinoBoardMega2560
http://arduino.cc/en/Reference/SoftwareSerial

It can be done in (many) other ways.

For example the very cheap 433MHz modules could be used with VirtualWire.
Every slave has to be an Arduino.
http://www.open.com.au/mikem/arduino/VirtualWire/

An ethernet or wifi shield can turn the Arduino into a simple webpage.
So you could control the Arduino with any PC or a tablet.
50  Using Arduino / Sensors / Re: MQ8 H2 sensor on: February 13, 2013, 04:25:35 am
After the burn-in time, they are reasonably stable.
But still for just one type of gas and indoors and for a certain air humidity.

I can't find in the datasheet how sensitive the MQ-8 is to oxygen. You have to test that.
Perhaps you need also an oxygen sensor : http://en.wikipedia.org/wiki/Oxygen_sensor
It seems that a galvanic oxygen sensor is used for simple measurements and a lambda oxygen sensor is used in cars.

The MQ-8 sensor uses 5V for the heat element. The sensor could get 50 or 60 degrees celsius (the metal on the outside). That should be avoided. Ask anyone who works at a natural-gas processing plant, they might freak out.
51  Using Arduino / Sensors / Re: Sensing people standing around a piece of artwork. on: February 13, 2013, 04:03:40 am
You could start with the MLX90614, that's hard enough to detect the number of people.
The temperature you measure depends on the temperature around. On a cold day it is easier to detect people.

I suggest to combine a few sensors.

At least add a PIR motion sensor. You could even use two of them, on the left and right side of the art object. You could use more PIR sensors, like a row of 5 or 7, and shield the front with a small opening for a small beam.

Ultrasonic sensors can measure the distance. For example the ping))) modules. Perhaps you should use just one. I don't know if the ultrasonic sound will interfere if you use more than one.

Some radar motion detectors are not expensive. But you need the complete module with variable sensitivity, not the radar elements without amplifier (as sold on Ebay).

A theramin is something that senses if someone is very close : http://en.wikipedia.org/wiki/Theremin

Measuring the weigth of the people in front of the art object with a weigth sensor in the floor is out of the question ?
52  Using Arduino / Sensors / Re: MQ8 H2 sensor on: February 13, 2013, 03:46:54 am
I have made a page for those sensors : http://playground.arduino.cc/Main/MQGasSensors
But they are not very accurate, and you have to figure out the ppm for the value yourself.
53  Using Arduino / Interfacing w/ Software on the Computer / Re: Interfacing techniques: Help!!! on: February 13, 2013, 03:45:06 am
You can emulate a usb keyboard with the ATmega328 using V-USB : http://www.obdev.at/products/vusb/index.html
If the computer has a serial port or parallel port or PS/2 port or game port, you could use that.
Or using bluetooth, with a bluetooth dongle in the PC.
Perhaps using ethernet or wifi.

And beside those, you could open a device (like a keyboard or a usb audio stick) and connect your ATmega328 to the circuit board of that device.
54  Using Arduino / Sensors / Re: Pressure Sensor on: February 12, 2013, 05:48:37 pm
Is the actual pressure sensor underneath the black rubber ?
And are there three pins to connect it ?

If you know the brand of the washing machine you can perhaps find how to use the sensor.
Is it one of these (click "See Larger Photo") : http://www.made-in-china.com/showroom/lucydeng1/product-detailLqimbMGPbNWH/China-Washing-Machine-Water-Level-Sensors-Pressure-Sensors.html


55  Using Arduino / Sensors / Re: Strange Analog Input Problem on: February 12, 2013, 05:31:52 pm
retrolefty, it is amazing how you solved it.

oldnoob, a good grounding is important. With sensors it is very important.
Perhaps you can make a drawing of it. Or you can stretch your circuit as one long circuit and check how the ground is.
The ground of the sensors should go the the ground of the Arduino, because the signal is going to the Arduino and that should be accompanied by the ground.
56  Using Arduino / Motors, Mechanics, and Power / Re: Can I Connect a DC Motor to the Transistor's Emitter? on: February 12, 2013, 01:31:31 pm
If the motor is connected to the emitter (and ground), the voltage could be that low.
Also, if you use a battery for the motor, it is best to connect the motor to the collector (and battery plus).

You can try for yourself, and measure the voltages.
But use a resistor of about 1k at the output of the Arduino. That way the Arduino output is protected in case you connect something wrong.
57  Using Arduino / Motors, Mechanics, and Power / Re: Can I Connect a DC Motor to the Transistor's Emitter? on: February 12, 2013, 04:25:58 am
Yes, that's also good.
But if the output of the Arduino is only 4.5V and the Vbe (voltage drop from base to emitter) of the transistor is 0.7, and the voltage drop over the resistor is 1V, the motor gets only 2.8V.

You also can't use a 12V motor.
58  Using Arduino / Motors, Mechanics, and Power / Re: three servos, 4 motors, LED's....How do I power all this stuff? on: February 12, 2013, 04:19:16 am
The first one depends on the motors. For an unregulated power supply I would prefer to use 15...25 V, and use DC-DC converters to make a good 12V for the motors.
The second one is a brandless cheap switching power adapter again. If you buy that, you probably have to buy a better version soon. Don't try to buy a good 12V 4A power supply for 10 dollars, that's not possible.

If you want something cheap, this one: http://www.mpja.com/12-Volt-Power-Supply-85A-100W-Switching-Hengfu/productinfo/16013%20PS/
But I'm not sure how it will behave without any load.

If you want something better: http://www.mpja.com/12-Volt-Power-Supply-51A-Linear-IHN12-51/productinfo/6609%20PS/
59  Using Arduino / Sensors / Re: Strange Analog Input Problem on: February 11, 2013, 06:48:40 pm
Use a resistor of 1k between sensor and Arduino input, to protect the Arduino. Perhaps the sensor generates a spike of 12V during startup.
Use an other input pin of the Arduino, you might already have damaged an input pin.

Did you set the internal reference of the Arduino ? (you should not).
Did you connect the sensor to Aref ? (that is not an input).
Did you connect Aref to something else ?
If the sensor is stuck at 2.24V, is that measured with the Arduino or with a multimeter ?

If you still have problems, we like to have more information.
Which Arduino Board ?
Please upload the sketch.
What sensor, please paste a link to it.
Can you draw how everything is connected.

If grounding is a problem, you could power the Arduino with a battery, or via the usb with a laptop with its power supply disconnected.
The impedance of an Arduino input is very high. It might even be higher than the impedance of the multimeter. So it doesn't make sense that the voltage drops.
60  Using Arduino / Project Guidance / Re: New to this. Need advice with USB mouse interface on: February 11, 2013, 04:10:49 pm
Yes, but the data path doesn't seem good to me.
I mean this: from gaming mouse to Arduino is possible, but the analog output to be able to use a multichannel analog input doesn't seem right to me.

Can you use an analog optical sensor and connect that directly to the A/D board ?

I'm not very familiar with Matlab setups, so I don't know what else would be possible.
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