MPXA4115A picbasic code

[ScaleRobotics]

Thanks Bitmaniac,

Don't let me worry you! The speed difference will probably have a bigger affect on your PWM sensing and pass through, than altitude conversion. But I think 8mhz is reasonable for this. Yours is the motor control for a glider, so even if it is a little glitchy, you are not going to notice much, since to get to altitude you will probably be at 50 to 100 percent throttle, or you will be at 0 looking for lift.

I was originally thinking of speed for the higher bit conversions, like 15 and 16 bit. But I think the speed of your conversion will be 2 us, where with 20 mhz, the conversion is 1.6 us. So just the 16 bit analog oversampling takes 100 ms with 20 mhz and 125 ms with your 8mhz internal. Not a big difference there! Of course the 15 and 14 bit samples are MUCH quicker.

So no, really, I think you will be fine.

[bitmaniac]

So you think I have to stick to my already made pcb and don't try an 20 MHZ crystal.
Here it is the final pcb in 3d and shematic I am going to use.
I am finishing the firmware part now thanks to Darrel ADC convertion and your help. I will use 14bit with 8mhz internal (12f683). The pcb will support ICSP an optional button and a led indicator. I have not try the pcb (in real) only in Proteus sim. I will let you know of the progress. for the moment take a look...

EDIT: in schematic the 100n pic decoupling is missing (in pcb is ok)

[ScaleRobotics]

So you think I have to stick to my already made pcb and don't try an 20 MHZ crystal.

I think your design is feasible. There is no harm in designing the board before the firmware is completed. But there might be some harm ($$$) if you have them made before testing. I would recommend that you wait till you write your PWM sensing and generating code, and test it, before you decide on a final layout. On a breadboard, adding a crystal is easy, if you need to...

[ScaleRobotics]

One change you might consider would be to change pin 5 (CCP1 HPWM pin) to your servo connector. That way if you decide to use the HPWM function for PWM out, you could go ahead and do it. You could always reverse your connectors if you decide you want to use the HPWM for PWM in. And if you wanted to make it really flexible, consider moving your two least important inputs/outputs to the crystal pins. You have enough space on your board for a resonator. Why not make some pads for inserting a resonator, and run your LED and Serial connector off of those traces. That way (if you have to) you can sacrifice the LED and serial for a crystal.

[bitmaniac]

You are in my mind actually I have already daone what you suggest but I had already develop and etced the above pcb version so I 'll give a try as it is and I have already residign the pcb with extra crystal pads BUT I have not implement the HPWM idea you suggest . It is a perefect idea I will add this too this weekend. Thanks.

[bitmaniac]

Reviced sch & and pcb...

I improved pcb (after suggestion from Scalerobotics).
Arm button removed (arm will be done by throtle or by default min ALT).
20Mhz crystal included. (although I did notice according to manual at 20Mhz HPWM for THR out has min limit to around 1221Hz not so good!)
(...also In Circuit fw update)

Working on Fw now. I have problems with HPWM though!

[ScaleRobotics]

Well, it looks like I convinced you to go with a crystal, and you convinced me to go without one. Pretty funny. Sorry about the bad advice I gave about the pwm. I didn't do enough homework.



Code and schematics here: http://sites.picbasic.net/component/...,91/pageid,81/

[flotulopex]

Thanks bitmaniac,

I have read Alain's explanation about "oversampling" and "rolling mean value" in a previous post but I'm still not clear why it is necessary to declare a DEFINE to do so.

I think, I don't understand what the DEFINE does.

Any clue for me?

[mark_s]

Thanks bitmaniac,

I have read Alain's explanation about "oversampling" and "rolling mean value" in a previous post but I'm still not clear why it is necessary to declare a DEFINE to do so.

I think, I don't understand what the DEFINE does.

Any clue for me?

Hello,
You are correct you should set the pic to 10 bits:
DEFINE ADC_BITS 10

http://www.darreltaylor.com/DT_Analog/

If you study Darrel's example in the above link, bottom of the article.
You set your oversampling resolution in this line:


ADbits = 12 ; set to 12-bit resolution

Regards
Mark

[Acetronics2]

I think, I don't understand what the DEFINE does.

Any clue for me?

Hello, Roger

DEFINE only set a constant ... used to DEFINE some processor module or macros configs.

the value is tested, and relevant settings are chosen by the compiler ( sort of conditionnal assembly - if you prefer ... sort of !!! )

just look at the difference ( in the asm listing) between DEFINE ADC_BITS 8 and ADC_BITS 10 ...

Should be little differences in the ADCONx setting values ... don't you think ???

Alain

[flotulopex]

Thanks Alain,

I was confused because of the value (16) in Darrel's code example.

I now understand what this particular DEFINE does