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stanleyella

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Joined: 25/06/2022
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Posted: 04:22pm 14 Jul 2023

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A linear pot say 10KR between 3.3V and ground and the wiper to a-d pin and use floats ie volts!=pin(31). should 0 to 3.3, see the results. math scale will scale it to say screen height or whatever if you want.

Mixtel90

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Posted: 04:58pm 14 Jul 2023

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The usual rotation angle for a standard pot is about 270 degrees. Anything that goes much past that is usually a multiturn pot or a rotary encoder. :) There are exceptions, but not all that common.

You can change the range of the ADC inputs and make them independent of the 3V3 supply. Connect a LM4040 3V0 precision shunt regulator to VREF and use OPTION VCC 3.0. The ADC inputs will then cover 0-3.0V.

The LM4040 is available in other voltages that you can use in the same way. 2.048V is useful for binary values. 2.5V is also available.
Edited 2023-07-15 03:05 by Mixtel90

Mick

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stanleyella

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Posted: 05:44pm 14 Jul 2023

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I think they use rotary pot on r/c servos maybe as I converted a couple to continuous rotation and posted on picaxe forum that you could then read the pot position.
long time ago.
https://www.youtube.com/watch?v=aa9sXwqO8GY&t=4s
Edited 2023-07-15 04:14 by stanleyella

stanleyella

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Posted: 07:05pm 14 Jul 2023

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I looked at my old gcbasic "oscilloscope" using arduino 328p and notice how stable it is compared to using pico. no trig.
https://www.youtube.com/watch?v=nyCjT879oZk

Mixtel90

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Posted: 07:51pm 14 Jul 2023

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That doesn't necessarily mean it's more stable, just that the display you are seeing isn't updating as quickly. That could be that the display system itself is slower or that the sample rate is slower. In fact, when using a digital scope, you reduce the sample rate in some cases to improve the display.

If you have a properly working triggered timebase set to single scan then one scan is triggered then that's it. The display can't be anything other than absolutely rock solid. If it isn't set to single scan then it will trigger each time the trigger condition is met, usually not in the middle of the current scan though. :)

Mick

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phil99

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Joined: 11/02/2018
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Posts: 2136

Posted: 10:35pm 14 Jul 2023

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@Lizby
In addition to the previous answers (a linear pot is what you need for uniform increments) the pot could be 'noisy'. Unreliable contact between the wiper and the carbon track results in a fluctuating voltage.
Adding a 100nF cap between AIN and Gnd. may help filter that out.

> setpin gp26,ain
> do:? int(303*pin(gp26)):pause 999:loop
2
2
35
208
312
445
582
670
764
858
953
999
999
999
999
>

Edited 2023-07-15 09:39 by phil99

stanleyella

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Posted: 01:21pm 15 Jul 2023

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Mixtel90 said That doesn't necessarily mean it's more stable, just that the display you are seeing isn't updating as quickly. That could be that the display system itself is slower or that the sample rate is slower. In fact, when using a digital scope, you reduce the sample rate in some cases to improve the display.

If you have a properly working triggered timebase set to single scan then one scan is triggered then that's it. The display can't be anything other than absolutely rock solid. If it isn't set to single scan then it will trigger each time the trigger condition is met, usually not in the middle of the current scan though. :)

It was years ago probably on a uno 328 10bit adc.
I tried lgt328 at 32MHz and 12 bit adc and think it was stable to. I don't know why sameish code on pico is unstable display ie doesn't start at same position, unless pico too fast for wave freq. I really don't know. Never mind, it was never meant to be a real scope, just playing with graphics and how easy to use them it is.

Volhout
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Joined: 05/03/2018
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Posted: 02:14pm 15 Jul 2023

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Picomite mmbasic can be interrupted by console. If you are reading adc in a mmbasic loop, such as DO:LOOP or FOR:NEXT, the speed of reading adc is not constant.
Settick is better, but the adc burst reads, has most stable timing of reading adc.

PicomiteVGA PETSCII ROBOTS

stanleyella

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Posted: 04:41pm 15 Jul 2023

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Volhout said Picomite mmbasic can be interrupted by console. If you are reading adc in a mmbasic loop, such as DO:LOOP or FOR:NEXT, the speed of reading adc is not constant.
Settick is better, but the adc burst reads, has most stable timing of reading adc.

the manual says to an array so no loops, cheers stan, it's not like 8bit.
Dim samples!(160)
adc open 500000,1 'samples per second
adc start samples!()'get new samples
math scale samples!(),80,samples!()

Mixtel90

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Posted: 05:15pm 15 Jul 2023

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Stop sampling when the array is full.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
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lizby
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Posted: 05:28pm 15 Jul 2023

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Thanks for the explanations. I found a bag of pots labelled 20K trimmer from a supplier I haven't bought from in probably over 15 years. It travels about 5/6ths of a turn, with detents.

Rounding to 2 decimal places there was very little dither--but a little bit--if I make sure that the change from the previous reading is no more than 1 one-hundredth, it looks like I will not see any dither.

setpin 31,ain
dim string a,b,c,
do: a=str$(pin(31),1,2): if b<>a then: b=a: ?a;" ";:endif:pause 1000:loop

Turning it back and forth gives this:

3.25 1.49 1.50 1.49 1.50 1.49 1.62 1.65 1.97 2.06 2.16 2.20 2.21 2.20 2.30 2.32 2.42 2.51 2.63 2.85 2.94 2.95 3.11 3.30 1.39 1.40 1.39 1.40 1.29 1.07 0.91 0.56 0.54 0.01 0.23 0.24 0.36 0.49 0.63 0.73 0.78 0.82 0.95 1.13 1.22 1.25 1.27 1.40 1.58 1.60 3.30 0.01 1.49 1.56 1.55 1.56 1.55 1.56 1.55 1.56 1.55 1.56 1.55 1.56 1.55

PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed

Mixtel90

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Posted: 07:44pm 15 Jul 2023

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Sometimes pots are marked with a letter to indicate their law:
A = audio taper (logarithmic or pseudo-logarithmic)
B = linear
C = reverse audio taper (as A but reversed)

Pseudo=logarithmic is usually two or three linear sections stuck end to end. For a type A pseudo log that will be a high resistance section followed by a lower resistance section(s) as the pot is turned clockwise.

There are also special 3-terminal pots (the look normal) where the centre is grounded and the two ends are both logarithmic! These used to be used for balance controls and are pretty rare now. Yet another sort has a centre tap on the track which is used with a capacitor to ground to create loudness controls. You rarely come across either of these wierdos now.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

phil99

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Joined: 11/02/2018
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Posts: 2136

Posted: 09:51pm 15 Jul 2023

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@Stan
See if this makes any difference.

Dim samples!(160)
adc open 500000,1 'samples per second
samples!(159) = 0 'set last element to 0
adc start samples!()'get new samples
Do : Loop Until samples!(159) 'wait till array is full
math scale samples!(),80,samples!()

Or if the last sample can be 0

Dim samples!(160)
adc open 500000,1 'samples per second
samples!(159) = -1 'set last element to -1
adc start samples!()'get new samples
Do While samples!(159) < 0 : Loop 'wait till array is full
math scale samples!(),80,samples!()

Or just to be different

Dim samples!(160)
Refresh.Rate = 500 'ms - must be longer than sample time
adc open 500000,1 'samples per second
adc start samples!()'get new samples
Pause Refresh.Rate 'wait till array is full
math scale samples!(),80,samples!()

Edited 2023-07-16 10:19 by phil99

zeitfest
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Joined: 31/07/2019
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Posts: 482

Posted: 02:38am 16 Jul 2023

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A pico project using 4 pots for analog inputs (Arduino based)

phil99

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Posted: 04:21am 16 Jul 2023

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@Stan
This seems ok.

MODE 2 'PicoMiteVGA "scope.bas"
Dim samples!(320)
ADC open 500000,1 'samples per second
Do
samples!(319) = -1 'set last element to -1
ADC start samples!() 'get new samples
Do While samples!(319) < 0 : Loop 'wait till array is full
Math scale samples!(), -72, samples!()
Math add samples!(), 240, samples!()
For n=0 To 319
Line n, 0, n,320, 1, 0
Pixel n, samples!(n), RGB(yellow)
Next
Loop

Volhout
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Posted: 06:11am 16 Jul 2023

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You can use an interrupt when done. No need for samples(319)=-1
Look at my mains voltage monitor, that reads into alternating arrays, when 1 is processed, the other is filled from adc.

Volhout

Peters latest ADC RUN can do this autonomously. But haven't tried it yet.
Edited 2023-07-16 16:12 by Volhout

PicomiteVGA PETSCII ROBOTS

phil99

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Posted: 06:41am 16 Jul 2023

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Quite right about the interrupt but I don't know if Stan has other interrupts in the program. The fewer the better.

Now with a graticule.

MODE 2 'PicoMiteVGA "scope test.bas"
Dim samples!(320)
Dim integer x, y
ADC open 500000,1 'samples per second
Do
samples!(319) = -1 'set last element to -1
ADC start samples!() 'get new samples
Do While samples!(319) < 0 : Loop 'wait till array is full
Math scale samples!(), -72 , samples!() 'scale to fit screen
Math add samples!(), 240, samples!() 'set 0V to bottom of screen
For x=0 To 319
If x Mod 40 Then
Line x, 0, x, 240, 1, 0 'Blank old trace
Else
Line x, 0, x, 240, 1, RGB(0,64,0) 'Time lines
EndIf
For y = 0 To 240 Step 30
Pixel x, y, RGB(0,64,0) 'Volt lines
Next
Pixel x, samples!(x), RGB(255,128,0) 'Trace
Next
Loop

Edited 2023-07-16 22:21 by phil99

stanleyella

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Joined: 25/06/2022
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Posts: 2129

Posted: 02:28pm 16 Jul 2023

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Lots to try with simple scope idea, thanks for the ideas. I tried the interrupt weeks ago but no luck. It's supposed to trigger when the array is full but not sure how to implement. The problem is that's not going to make the samples start at the same point on a repetitive waveform.
I tried do until sample! >1 and sample!<1.1 :loop
Then start sample array but no display.
I'll try the code posted. cheers, stan

stanleyella

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Posted: 06:41pm 16 Jul 2023

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my code drew lines between the a-d values and erases each then redraws new so visually looks fast
dim count%,samples!(160),old_samples!(160)
SETPIN GP26, AIn
adc open 5000,1 'samples per second
cls
do
adc start samples!() 'get new samples
math scale samples!(),79,samples!()'scale to 80 pixel
for count%=0 to 158 'screen width
line count%,old_samples!(count%),count%+1,old_samples!(count%+1),,rgb(black) 'erase old_sample
line count%,samples!(count%),count%+1,samples!(count%+1),,rgb(white) 'draw new sample
next count%
math add samples!(),0,old_samples!() 'copies new samples to old_samples
loop

NPHighview

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Joined: 02/09/2020
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Posts: 200

Posted: 08:18pm 16 Jul 2023

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Here's a non-interrupt-driven double-buffered version for use on the WaveShare Pico-Eval-Board (480x320 LCD). Sorry, I don't have a PicoMiteVGA (but this should work fabulously well on a Colour Maximite 2):

'PicoMite "scope test.bas" for WaveShare P-E-B (480x320) (Landscape mode)
'Adapted by NPHighview from Phil99 on the Backshed Forum July 2023
'Adds double-buffering and array graphics (FAST!)
'Next on the to-do list: add interrupts.

Dim Buffer1!(480), Buffer2!(480), Horizontal!(480)

Dim HGratx1(13), HGraty1(13), HGraty2(13)
Dim VGratx1( 9), VGratx2( 9), VGraty1( 9)

Dim integer x, y

Const Background = RGB(48,64,48) ' medium dark grey/green a la Tektronix
Const Graticule = RGB(black)
Const Signal1 = RGB(yellow) ' dual colors used for debugging double-buffering
Const Signal2 = RGB(yellow)

' Pre-set buffer values for use in fast array graphics

Math Set 0, Buffer1!() : Math Set 0, Buffer2!() ' Pre-set Buffers to draw lines at the bottom
Math Set 0, HGraty1() : Math Set 320, HGraty2() ' Pre-set Arrays for Horizontal Graticules
Math Set 0, VGratx1() : Math Set 480, VGratx2() ' Pre-set Arrays for Vertical Graticules

For x = 0 To 479 : horizontal!(x) = x : Next x ' used in array graphics
For x = 0 To 12 : HGratx1(x) = x*40 : Next x ' for time graticule
For y = 0 To 8 : VGraty1(y) = y*40 : Next y ' for volts graticule

' Set up the screen and ADC hardware

CLS Background
ADC open 500000,1 'samples per second

' Begin signal acquisition and display

Do
' While acquiring Buffer 1, display Buffer 2

Pixel Horizontal!(), Buffer1!(), Background 'Clear previous display of Buffer 1
Buffer1!(479) = -1 : ADC start Buffer1!() 'Start Acquisition into Buffer 1
Line HGratx1(), HGraty1(), HGratx1(), HGraty2(), 1, Graticule ' Redraw overwritten
Line VGratx1(), VGraty1(), VGratx2(), VGraty1(), 1, Graticule ' Graticules
Math scale Buffer2!(), -108, Buffer2!() 'Scale Buffer 2 to fit screen
Math add Buffer2!(), 320, Buffer2!() 'Offset Buffer 2 to bottom of screen
Pixel Horizontal!(), Buffer2!(), Signal2 'Display Buffer 2 scaled/offset
Do While Buffer1!(479) < 0 : Loop 'Wait until Buffer 1 is full

' While acquiring Buffer 2, display Buffer 1

Pixel Horizontal(), Buffer2!(), Background 'Clear previous display of Buffer 2
Buffer2!(479) = -1 : ADC start Buffer2!() 'Start acqusition into Buffer 2
Line HGratx1(), HGraty1(), HGratx1(), HGraty2(), 1, Graticule ' Redraw overwritten
Line VGratx1(), VGraty1(), VGratx2(), VGraty1(), 1, Graticule ' Graticules
Math scale Buffer1!(), -108, Buffer1!() 'Scale Buffer 1 to fit screen
Math add Buffer1!(), 320, Buffer1!() 'Offset Buffer 1 to bottom of screen
Pixel Horizontal(), Buffer1!(), Signal1 'Display Buffer 1 scaled/offset
Do While Buffer2!(479) < 0 : Loop 'Wait until buffer 2 is full

Loop

End

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