I want to order a gyro ( LPR550AL Dual-Axis ) from one of your partners, and I have some questions first. I have read the datasheet of the gyro, but still no answer for me.
First of all, the use of Vref pin is necessary ( something like… do i need to connect it with the 3.3V line, or the GND line, or just leave it unconnected ) ?
I am going to use the gyro with a 3.3V microcontroller, and I already have 3.3V regulator on my board, so I won’t use VIN.
Second question, which output has less noise on it ? the 4X or the X ? because I did not get the exact idea behind x and 4x. I mean… 4x gives a resolution 4 times bigger than X or… ?
Vref is an output. The outputs of the gyro are centered around the voltage of Vref. It is not strictly necessary to use Vref, but it might help with calibrations. You could also use Vref with analog circuits, comparing it with the outputs.
Yes, 4X gives you more resolution while reducing the range of values you can measure. The 4x output is just an amplified version of the same basic signal, so it is not going to have less sensor noise in some fundamental way. However, there are many sources of noise, and not all of those will be amplified by 4x. Also, the amplification is done on the same chip with the same references, temps, etc., so that amplification is less likely to introduce noise than any off-chip amplification you might consider.
When I looked at the x and 4x outputs on an oscilloscope with the board just sitting on my desk, and with 20MHz bandwidth limiting, there was basically no difference between the noise on the two pins. So, ultimately, your decision on which outputs to use should depend more on what range is appropriate for your application than on concerns over one signal being of better quality than the other.
I want to use the gyro for a remote controller ( something like Nintendo’s Wii Remote ), but for planes and stuff like that, so i will hold the remote quite steady in my hand, i’m not going to play tennis with it or stuff like that.
Vref should be something like half of the voltage Vdd supplies ? And the most important part, Vref varies ? I mean… i have about two ADCs left on my microcontroller ( besides X and Y from the gyro ), and one of them i could use to measure the voltage on Vref, but when will I do this ? I mean… do I do a boot-read, or do I have to read sometimes ( something like every 10 seconds ), or read the Vref everytime I read X and Y, and do a little processing on it ?
Second… I did not quite understand the X-4X.
I have a 3.3V uC ( PIC24something ), and which pin should I use, X or 4X so I can benefit of the maximum resolution of the sensor ? Anyway I don’t need many degrees or a very very high resolution, because after I will read the value on a 10-bit resolution, i will divide the result by ten or even more, so I would have a quite steady voltage when i hold my remote in my hand and let’s say concentrate to keep it steady and not move it. Also I have 2 joysticks ( potentiometers ) on which I will do the same thing… because I don’t really need 1024 values for when I move my finger on it… about 25 values i think it’s pretty good.
So, which one should I connect, X or 4X to my uC ADC ?
Oh and please help me check my other connections: the Vin pin will be left unconnected, PD and ST unconnected, Vdd to my 3.3V regulator, GND to my regulator’s ground, and what’s left of the X-Y pins ( either X-Y either 4X-4Y ) unconnected. And the rest ( X, Y let’s say, and Vref ) to my uC ADC. Is it correct ? Also please don’t forget to clear me out with the Vref thing.
Did you look at our product page and the datasheet for the gyro? On our page, we say:
The point is that Vref is what tells you what zero is; when you read your x and y outputs, you compare it to Vref.
I don’t know what you don’t get about the x and 4x. One pin gives you more range, the other more resolution in terms of degrees per second per bit of your ADC conversion. If you don’t need the range or resolution, why do you care so much? Also, this is one of those cases (as opposed to something like trying to apply power both ways) where you can just try both and see which works for you.
I’ve got another problem now.
I got the gyro and measured it with my oscilloscope and found out something I did not expect.
I’ve assumed that when the gyro is positioned at 0 degrees by either plans, it would give the Vres voltage on the 4X and 4Y pins ( form now on I use only the 4X and 4Y, not the X and Y ). And it did. I thought that when I move the gyro to have something like 45 degrees on each of the plan, the gyro would report me a voltage where I would know I am at 45 degrees. The problem is that the voltage comes back to Vref when i stop moving.
Also, the voltages should be for example when i move on one direction 45 degrees something like: Vref + 2mV*45. I’m not pretty sure about that.
Can you please clear me out on this ? thanks
And also, when I will put it on my microcontroller board, how can i determine the position my remote controll is in ? ( the whole idea behind buying this gyro was to know how my remote is tilted - X and Y axes ).
What you describe is exactly what a gyro does - it measures the rate of rotation. When you stop rotating, outputs go to zero (or Vref). An accelerometer can be used to do something closer to what you want, though readings can be affected by motion other than the turning that you care about. For totally precise tilt measurements, some devices combine accelerometer and gyro readings.
Okay, but now I only have a gyro, and I want to measure the tilt and pan of my board ( which is a RC ).
What shall I do ? Have a reset button when I have my remote on horizontal position, and then continuously read data from the gyro and add or substract angles ? Is my logic ok ?
I am asking because I think that there maybe is someone who already had my problem and can tell me a solution, so I don’t waste another week in finding it.
Continuously integrating the angles, if done well, can let you keep track of your angle for a minute or maybe more, so if that solution sounds good to you, you could go with it.
But since I do not know the exact constraints of your project, and since the whole purpose of a gyro is to do things with angles, your question is basically the same as “what can I do with a gyro?”. I think that the most useful thing you can do now is go search Google for what other people have done with gyros.
You cannot make accurate pan and tilt measurements with just a gyro. Gyro measurements drift over times as short as a few seconds. As Paul said, you need both a gyro and a accelerometer. You then need to combine the data from both devices. Google “kalman filter” for more info. You can build the circuit yourself, or get this board: pololu.com/catalog/product/1263.
I did not say that he needs both a gyro and an accelerometer, and I certainly do not think that it is necessary for doing something fun with remote control gestures, which is what I think he wants to do.
