I am using a third part Duemilanove from DF ROBOT.
I have a muscle sensor that output analog signal. Let say a range between 1.0v to 3.0v roughly. But when I connect the sensor with Arduino using A0, the voltage jumps by almost 5v exactly. So if i use a multimeter to test the output voltage of the muscle sensor , I get around 6v - 9v. As a result, of course, it is out the range that an arduino accepts.
It is very strange that I couldn't figure out why the analog input voltage is altered every time it is connected to the Arduino.
Hi There, My sensor is this one. And I am very sure I connect the GROUND to the right GND pin...To make sure, I also connect the GND pin to one of the analog input to test it... It is ground.
Connect your voltmeter negative (-) lead to what you use as ground to measure the output voltage. Then use the positive (+) lead to check the ground connection for the sensor. It should show 0 volts. Does it?
Also, I don't think the voltage is offset. Because when I connect the sensor to the Arduino, the voltage changed to around 5.6v and sensor voltage output is not responded to muscle activities.
If you connect that circuit directly to your arduino then you are in danger of damaging your arduino.
You can't drive the analogue inputs greater than the supply voltage without causing damage.
You need at least two catcher diodes and a series resistor, see:- http://www.thebox.myzen.co.uk/Tutorial/Protection.html
Also, I don't think the voltage is offset. Because when I connect the sensor to the Arduino, the voltage changed to around 5.6v and sensor voltage output is not responded to muscle activities.
That is one reason as to why it is the offset voltage causing you problems.
Hi. Thanks for your suggestion, But originally, my sensor output values between 1- 3 volt. It is out exceeded the 5v limit of Arduino. But it changed straight to 5.7v after connection. Is that still because of the same reason you suggested?
How do you define connection? Is it just the one wire or are we talking about the ground as well. Getting 5.7V on the input to a system that has only 5V of power is a bit impossible without that voltage being present on the circuit in the first place.
So I assume you have a +ve and -ve power supply with a center ground, what voltage are these? Connect that ground to the arduino ground and measure the voltage output before and after you connect it to the arduino's analogue input.
I have one analog output from sensor connected to one of the analog pin of Arduino, then ground to ground as well.
Yes, I have +/- 9v supply with a center ground. I tried only connecting the ground of sensor to ground of the Arduino before I connect the analog input to any A pin. The voltage output becomes 8.5v, which is totally bizarre. At the same time, any muscle activity won't alter the voltage output.
Luckily, I borrowed my colleague's UNO and it works perfectly without any alteration. So it is the problem of my Arduino then. I am using a DFRduino Deumilanove. Don't know whether mine is broken or any driver problem....I tried to use on-board power supply connect to a potentiometer and send to Analog input (following the arduino tutorial). It works normally.
As you have a +/- 9V supply you need protection on the arduino even if the circuit does not normally produce voltages above 5V and below zero. This is because it very easily could produce these voltages. It there were voltage spikes you would never even see them on a meter you would need a scope.
Any idea what happen here?
My guess is that you fried your arduino pin on your unit. Add that protection before you fry your friend's Uno.
Have you got any idea why if I only connect the GND on my sensor to the GND on the arduino. The voltage output jumped to 8.5v. . I fried the GND as well?
I would start by checking the power supply to the sensor board. You are powering it with the two 9v batteries? When you connect the ground to the Arduino, check the voltage on the batteries. Both the same?
Then I would start at the output op-amp, and work back through the op-amps outputs from each stage. Find which of the outputs is changing when the ground is connected to the Arduino.
edit: And I would be certain the GND connection on the Arduino is still GND. Maybe there is a problem with the GND pin on your Arduino. I would do a continuity check from the pin to a known good ground point on the board. Zero ohms is best.