ad pot fastest response!

[Alaskanphoenix]

HI,
i must poll 7 pots on a 16f88 and send a message only when the pot is used,i tried to write and read the adval on the on-chip eeprom but it is a very slow process and i need a fast response!
Any idea or code example?

Thank you very much

[Dave]

Alaskanphoenix, Is there some reason you are writing the value to EEPROM?

Dave Purola,
N8NTA

[Alaskanphoenix]

My programming skill is very low, so i write in eeprom only for my laziness!
But i thing it is not very good!

Thanks

[mister_e]

if you plan to do something usefull with those value when the power is removed and then power up.. i'll suggest to detect the when the power is remove and then save your value to the EEPROM.

I know Melanie already posted something on that with the according circuit... can't find it as now.

ow if you need for speed, don't use ADCIN but read/write and configure your PIC A/D yourself. not hard, code space saving and much faster. OK for assembly too but... accessing register in PBP could be really fast enough.

[mister_e]

OK got the post of Melanie

http://www.picbasic.co.uk/forum/showpost.php?p=3452&postcount=3

So now, depending of your current stuff, you may use Interrupts (on PORT change, INT0, INT..., Analog comparator...) or polling the PIN for a low level. quite simple to do.

[Alaskanphoenix]

thank you Mister_e

i already use the ad configuration registers,but the polling of the 7 pots isn't fast enough!I read instant interrupt post and I think i must use the A/D Converter Interrupt but i don't understand how to configure and use interrupts! Could you post an example or another way to poll the ad pins and send only the one is used?

[mister_e]

A/D interrupt will be produce ONLY (as i remind) if a A/D conversion is finished.

We really don't know what you'll do, what you need to do so we can just throw some idea now. Help us and describe exactly what you need to do. That way we will avoid to waste your and our time.

[Alaskanphoenix]

You are right!
I use a 16f88 to control 7 pots connected at the 7 ad pin and 3 bottons, one to calibrate the pots and the other to send midi control change messages.The pots, when rotated, must send midi continuos change message through the ausart.The ausart is configured comply with the midi protocol(31250 baud).this is an example of the midi message:

define osc 20
define HSER_TXSTA 20h ' enable TX register
DEFINE HSER_RCSTA 90h ' enable RX register
define HSER_BAUD 31250 ' midi baud rate

for j = 0 to 6
RESULT[J] = NEW[j]
ADCON0 = %11000001 + (J*8) 'SET A/D rC + A/D = ON
PAUSEus 10 'PAUSE 10uS FOR CHANNEL SETUP
ADCON0.2 = 1 'SET GO/DONE-BIT + START CONVERSION
PAUSEus 10 'PAUSE 10uS FOR CONVERSION
RESULT[J] = ADRES
RESULT[J] = RESULT[J] >> 1
'read j, NEW[j]
if RESULT[J] <> NEW[j] then
'write j, NEW[j]
hserout [$b0, j, RESULT[J]]
endif

next j
goto loop

RESULT is the value of the controller comply with midi,it must be 0-127
$bo is the statusbyte, j the channel.
The problem is that the program sends midi messages continuously,i want it sends midi only when the pot is rotated, sending all the values untill i stop to rotate!
Also i want to limit the range of the pot with the calibrate button,when i first press the button i set the min value to 0, then i rotate the pot to set another value corresponding to 127 pressing the button.

Thanks

[mister_e]

sounds familiar with tons of recent MIDI controller i built here.

OK let's try to do some rough explanation
-------------------------------------------------------------------------------------------------------------------------
1.i want it sends midi only when the pot is rotated, sending all the values untill i stop to rotate!

what i suggest, is to store every POT valu in an array variable or different variable for each pot. You'll read ALL pot in a continuous loop then compare the result you have with the according variable or Array Index. Sure you'll have to insert a error percentage as the AD result may vary a little bit.

Once you have a different value you send it on the MIDI line.

-------------------------------------------------------------------------------------------------------------------------
2. i want to limit the range of the pot with the calibrate button,when i first press the button i set the min value to 0, then i rotate the pot to set another value corresponding to 127 pressing the button.

Perfect situation to introduce some POWER-UP check up. To make things clear figure the following. When you power up your system, you check if one (or more) specific push button are press, if so, you jump to the calibration routine
In the calibration routine, a LCD or XYZ LED will prompt for a start point on POTx, you place the pot to the according position then you press on a button. Once it's done same thing apply to the end point. Same for all POTs. Once it's done, it's up to you what you'll do as calibration confirmation.

Calibration must be store in a external EEPROM (or internal if available). When you boot your system, it just read the calibation and store them in some variables.

Hope this help

[Alaskanphoenix]

Thank you mister_e!
It's time to experiment!

I'll try some of your suggestions

Bye

[moyejw]

Alaskanphoenix, I'm not familiar with pbp syntax but try something like this IF...THEN statement in place of yours--

IF RESULT[J] = ADRES THEN NoCHANGE
CHANGE RESULT[J] = ADRES
/calculate mididata :see below
/send mididata
NoCHANGE NEXT J

To convert your AD input to proportional value between 0 and 127---
/this is simiiar to Farenheit to Centigrade temp conversion

You need these values from when you calibrate your pots. JCALLOW, JCALHI
are values received @ CALIBRATE BUTTON1. BUTTON2

JMIDIVALUE=127(ADRES - JCALLOW)/(JCALHI - JCALLOW)

[moyejw]

I'm not familiar with pbp syntax but try something like this IF...THEN statement in place of yours--

IF RESULT[J] = ADRES THEN NoCHANGE
CHANGE RESULT[J] = ADRES
/calculate mididata :see below
/send mididata
NoCHANGE NEXT J

To convert your AD input to proportional value between 0 and 127---
/this is simiiar to Farenheit to Centigrade temp conversion

You need these values from when you calibrate your pots. JCALLOW, JCALHI
are values received @ CALIBRATE BUTTON1. BUTTON2

JMIDIVALUE=127(ADRES - JCALLOW)/(JCALHI - JCALLOW)

[blainecf]

If you make the assumption that only one pot at a time is changing (unless you're an octopus and have 8 hands on 7 pots), you could do this:

[Pseudocode]

1. read one pot
2. compare to previous reading (see above threads)
3. if a pot changes
3a. Act on the change
3b. (now for the assumption) Instead of advancing on to the next pot, decrement your pot pointer so that the same pot will be read again (which will cancel out step #4, below)
4. increment your pot pointer
5. loop to #1

Why? If you assume one hand on a pot, once you start changing, probability suggests that you'll continue changing that pot. Assuming that that one pot is still changing, and therefore, re-reading, you'll save time NOT READING 6 other pots that, in all likelihood, are not changing!

Regards,