Stable ADC readings

[dream-]

I am trying to get stable ADC readings.

I got a PIC 16F688 hooked up to a battery with a voltage regulator and with proper bypass capacitors. Each time I poll the ADC using ADCIN I get a different reading. Even averaging 50 samples is not enough to get a stable value. I have tried both internal and external oscillators (up to 20MHz).

I am testing it using a simple voltage divider with two resistors of the same value so that I get a value around 512 (ADC in 10 bit mode).

Is there anything I can do to stabilize the readings? And what is the source of all the noise?

Typically I am getting values oscillating from 432 up to 457, that's about a 5% oscillation.

There has to be a way to make the readings more accurate.6

[Jumper]

If you use VDD as the voltage reference for your AD then it is most likely a not stable powerline. I know you said battery and voltage regulator but have you tried to measure the VDD with an ocsillocope?

If you really need to get high accuracy reading you might have to consider an external high precition voltage reference. That one you can connect to the VREF pin and then you can set up the AD to use that one.

Also if you are switching other stuff while doing the measurement it might affect the power supply to the pic as well.

I would start with making sure the power nice and clean and batteries are not the best source when you start doing new designs.

[Acetronics2]

Hi,

May we get a scheme , plus your program ???

Crystal ball is out of range ...

Alain

[sayzer]

Adding to what Jumper said, I also face similar issues.
Usually, using 7805 or 78L05 may not provide a stable 5V.
Say it is actually between 4.98V and 5.02V. (approx 5% datasheet statement)

So, if you are using 10-bit reading there is your problem.
Eventually, Jumper's suggestion of having a high precision voltage reference is a good idea.

Another issue :
Pausing 2ms after each ADCIN command may help.

[mackrackit]

And...

More CAPs.
A capacitor from the ADC pin to VSS will help smooth things out. Will not make up for a bad power supply though.

[Acetronics2]

Hi, Sayzer

I am testing it using a simple voltage divider with two resistors of the same value so that I get a value around 512 (ADC in 10 bit mode).

That means he works in ratiometric mode and supply changes do not interfere here ...
so, problem is elsewhere ...

Alain

[karlos]

Hello to all
I'm new in this forum and there is no other way to tell this: i'm the most ignorant in terms of electronics.
My english also sucks, but i will try my best to communicate.
I have the same Mazoul72's issues. I have the same steering wheel remotes and want to build some interface PIC based to enable the buttons to work with my Kenwood DNX5260BT, but in the last months i have been looking for the kenwood values, but achieve to nothing and i'm so frustrated. It appears that Pioneer's communication protocol is the resistive type, but kenwood is via data and i don't know what to do.
Do you experts think that is possible to build one interface like the mazoul72 did and try to change the values in order to work with kenwood?
Or, what else can i do? I have a ir remote control that works with radio. This is a good think?

Thank you all
Karlos

[mazoul72]

Hello Karl ,
glad to see you in this forum .
I hope that you will find for this new type of Car radio steering wheel command's .
I had news and very usefull help from mister_e , i hope you will have these information .
Do you have a Line-K or Bus can wires behind your radio car ?
Perhaps , it is the best to access to all car radio commands ??

Regards.
Mazoul72