Analog Input

[Pandagineer]

Hello. I would like to measure the voltage of an external sensor using an analog input. I have the prototype deck. (And also the flow deck and CrazyRadio, FYI.) I understand there are analog input channels A0 thru A4, and ground.

If I digress for the moment, I'd like to say that I love this tutorial: https://www.bitcraze.io/documentation/tutorials/getting-started-with-stem-drone-bundle/, because I more or less understand all the code. I ran it successfully.

Back to analog input, I found this post: https://forum.bitcraze.io/viewtopic.php?t=2908. It seems like I need the two *.h files, deck_analog.h and deck_constants.h. That's understood, but...

1. how do these two *.h files fit into the bigger picture? Do I need a third file as the "main program", which somehow calls them? Can I call them from the flow deck tutorial I mentioned above?
2. In the two *.h files, where do I specify the channel? i.e. let's say I use channel A2. Would I type "A2" somewhere?
3. Note that the flow deck tutorial is written in PY, whereas the two analog input files are in C. I'm generally confused on when to use PY vs C. My preference is python. Are there python versions of the deck_analog and deck_constants files?

Thanks for the help!

[krichardsson]

HI, and thanks for the kind words on the stem drone tutorial. We're happy you found it useful!

I'll start with your question 3: The simple answer is that you use python for code that run in the PC and C for code that runs in the Crazyflie. In this case you will have to write some code in C to make the Crazyflie read your analog input. I guess that you maybe also want to use the analog value in your PC and to make this work you will have to write some code in the Crazyflie (C) that "publishes" the data and some python code for the PC that reads the values from the Crazyflie an does something useful with it, like printing or graphing the value.

Question 1: One way to look at header files (in general) is that they describe other parts of the code, for instance the signature of a function or, as in this case some constants that can be used in a function. deck_constants.h describes (defines) the pins on the expansion bus, while deck_analog.h describes the functions used for analog pins. You need to include header files in .c files before you use a function or constant, to tell the compiler that they exist.
You can not use the .h files from the tutorial code, as this is python.

Question 2: You include the header files at the top of a .c file and then use the functions and constants in your code. Something like this:

#include "deck_constants.h"
#include "deck_analog.h""

float readMyAnalogPin() {
    return analogReadVoltage(DECK_GPIO_MISO);
}

Check the Expansion port pinout to figure out which pin constant to use. In the example above DECK_GPIO_MISO is the same pin as A3

• You can read the Getting started with development to learn how to build and flash C code to the Crazyflie.
• The easiest way for you is probably to write an app in the Crazyflie
• If you want to make your value available to a python scrip, the logging frameworks is the easiest way

[krichardsson]

No this is not a problem related to your implementation. If there is no positioning data sent to the kalman estimator, the noise from the IMU will make the estimate slowly drift away and when it is too unreasonable the supervisor will reset it. This is what you see.

[Pandagineer]

Ok. FYI, I ran observed the console again. Out of 165 echos, 6 of them were the Kalman reset (3.6%). Then I commented out all data collection in the code, and instead printed "hello world". Now out of 82 echos, zero were the Kalman reset (0%).

There certainly seems to be a correlation with what my code is doing. If the Kalman reset is not a problem, I'm ok. I just wanted to let you know.

[krichardsson]

Thanks!
If you shake the CF a bit you will probably get some more as well :-)

[Pandagineer]

Update. I am successfully measuring the voltage of an external 1.6 V battery between pins A3 and GND. (Yay!)

My next questions (let me know if I need to start new discussions):

1. when I disconnect the external battery, the output sometimes goes to zero (roughly 10 mV), but then sometimes jumps to 3V. In practice, I will need the signal to stay at zero volts when I my sensor is reading nothing. (I don't mind averaging to filter noise, but if it jumps between zero and 3V, this would not work.)

2. When I apply -1.6V (i.e. I reverse the external battery), the Console stops echoing, and the M4 LED turns off. Will doing this damage the CF? If negative voltage is bad, how low is ok (i.e. can I give it -1 mV? -10 mV?) What is happening here?

For reference, my code is below. Thanks.

#include <string.h>
#include <stdint.h>
#include <stdbool.h>

#include "app.h"

#include "FreeRTOS.h"
#include "task.h"

#include "deck_constants.h"
#include "deck_analog.h"

float readMyAnalogPin() {
return analogReadVoltage(DECK_GPIO_MISO);
}

#include "debug.h"

double y;

void appMain() {
DEBUG_PRINT("Waiting for activation ...\n");

while(1) {
vTaskDelay(M2T(500));
y = readMyAnalogPin();
DEBUG_PRINT("%f", y);
DEBUG_PRINT("\n");

}
}

[krichardsson]

Yes please start a new discussion :-)