Hello,
I am developing a project that consists in controling a micro servo motor using the audio output of a smartphone (iphone/android, etc).
I have used this scheme: (source: http://www.gluemotor.com/how-to-make)
I also made the control signals (50hz, 1-2ms pulse) with matlab, and exported in .wav format.
Here is a caption of the signal (audacity):
Right now I am able to control up to 2 servo motors (one per audio channel) with my iphone, just reproducing the audio files.
The main problem is when I try to do this with an android-based smartphone. All the android devices that I have used so far are not able to provide enough signal to run the servomotors.
I read about how the control signal must be. I found that it is just a voltage signal that uses the values 0-5v. (0 for no signal and 5v for the peaks).
I have not an oscilloscope, but I am pretty sure that the android devices that I have tested do not provide the voltage required of 5v.
So to fix this problem I need to amplify the signal in order to get 5v on the peaks.
I though that operational amplifiers may help me. So I get some 741 op-amp's and I mouted using the non-inverting scheme.
The problem is that the output signal do not work with the servos. I have used a 1.5 battery to test the circuit (input), and the output was 2.75V using a 2.2k and 4,6k resistor (that is close to the ideal output of 3V).
So the circuit seems to work well with a DC signal and having trouble with the "AC" one.
Anybody can figure out where is the problem?
I am using a 5v cellphone transformer to feed the op amp. I am using only 5v because this motors will be a part of project thats need to be powered up with 4 1.5 batteries.
I read that the op amps like 741 are able to manage signals with no much delay and distortion below 1mhz, so the signal generated for the servos should not be a problem.
I am completely lost, any help will be fantastic.
Sorry for my bad english.
PD: I have posted the same information on the forum allaboutcircuits, I post here the same for reaching most people possible.
I am developing a project that consists in controling a micro servo motor using the audio output of a smartphone (iphone/android, etc).
I have used this scheme: (source: http://www.gluemotor.com/how-to-make)
![cache.php](/forums/proxy.php?image=http%3A%2F%2Fforum.allaboutcircuits.com%2Fcache.php%3Furl%3Dhttp%3A%2F%2Fimageshack.us%2Fscaled%2Flanding%2F837%2Fvhc1.png&hash=47b7f458ebc9f0b82f2fb7e26844ca5a)
I also made the control signals (50hz, 1-2ms pulse) with matlab, and exported in .wav format.
Here is a caption of the signal (audacity):
![mydn.jpg](/forums/proxy.php?image=http%3A%2F%2Fimg5.imageshack.us%2Fimg5%2F4429%2Fmydn.jpg&hash=51d4239a0b4d057c214d22515262904b)
Right now I am able to control up to 2 servo motors (one per audio channel) with my iphone, just reproducing the audio files.
The main problem is when I try to do this with an android-based smartphone. All the android devices that I have used so far are not able to provide enough signal to run the servomotors.
I read about how the control signal must be. I found that it is just a voltage signal that uses the values 0-5v. (0 for no signal and 5v for the peaks).
I have not an oscilloscope, but I am pretty sure that the android devices that I have tested do not provide the voltage required of 5v.
So to fix this problem I need to amplify the signal in order to get 5v on the peaks.
I though that operational amplifiers may help me. So I get some 741 op-amp's and I mouted using the non-inverting scheme.
![cache.php](/forums/proxy.php?image=http%3A%2F%2Fforum.allaboutcircuits.com%2Fcache.php%3Furl%3Dhttp%3A%2F%2Fimg692.imageshack.us%2Fimg692%2F613%2F0p7e.jpg&hash=fba7a8b8787f598d555da3c2588ff7d2)
The problem is that the output signal do not work with the servos. I have used a 1.5 battery to test the circuit (input), and the output was 2.75V using a 2.2k and 4,6k resistor (that is close to the ideal output of 3V).
So the circuit seems to work well with a DC signal and having trouble with the "AC" one.
Anybody can figure out where is the problem?
I am using a 5v cellphone transformer to feed the op amp. I am using only 5v because this motors will be a part of project thats need to be powered up with 4 1.5 batteries.
I read that the op amps like 741 are able to manage signals with no much delay and distortion below 1mhz, so the signal generated for the servos should not be a problem.
I am completely lost, any help will be fantastic.
Sorry for my bad english.
PD: I have posted the same information on the forum allaboutcircuits, I post here the same for reaching most people possible.