PC based Oscilloscope

johnson kennady said:

i connected an analog signal to A1 pin from function generator with a frequency 25hz.

johnson kennady said:

i used temperature sensor moniter program

Are you sure that temperature monitor program sample rate is high enough for 25Hz signal? You need at least 250 samples per second sampling rate here. If sample rate is less than 50Hz, then output most probably will be like you see now - seemingly random data.

johnson kennady said:

2.how to get all ADC Value (from 0000, 0001, 0002,0003, 0004.,005 upto 1024) through hyperterminal?

Huh? What's exactly your problem? I would say: use hex coding and that's it. If data shall be human-readable in hyperterminal, then show it as ASCII decimal numbers.

sir, thanks for your quick reply

i'm made some modification in the temperature sensor monitor program. here it is

 P2DIR |=0xFD                                                                                                                                                                       ;
    P2REN = 0x02;
    ADC10AE0 = BIT1;
    ADC10CTL1 = INCH_1 + ADC10DIV_7;       // Temp Sensor ADC10CLK/8 and analog input to A1
    ADC10CTL0 = SREF_1 + ADC10SHT_3 + REFON + ADC10ON + ADC10IE + ADC10SR;
    for( degC = 240; degC > 0; degC-- );    // delay to allow reference to settle
    ADC10CTL0 |= ENC + ADC10SC;             // Sampling and conversion start
    __bis_SR_register(CPUOFF + GIE);        // LPM0 with interrupts enabled
    results[0] = ADC10MEM;

ADC10SR (sampling rate) is 50ksps(from datasheet) which is greater sampling rate than you mentioned(250 samples) . so that i gave 25hz analog signal (sample rate = 2* input frequency).

in my visual Basic program, i'm export hyperterminal value to picture box via serial port. oscilloscope wondow draws a line as per hyperterminal value . but my hyperterminal output looks like this as below

0000

0234

0576

0999

0345

0096

0000

0124

and goes on. it receives random value as you said.

but if hyperterminal receives all ADC value like this

0000

0001

0002.

.

.

0100

0100

.

.

.

1023

1022

1021

.

.

0500

0499

.

.

0001

0000

i will get pure sine wave in the oscilloscope window
   

johnson kennady said:

ADC10SR (sampling rate) is 50ksps(from datasheet) which is greater sampling rate than you mentioned(250 samples) . so that i gave 25hz analog signal (sample rate = 2* input frequency).

This is capability of ADC, not necessarily actual sample rate. How often ADC values are actually read and transmitted to your application - is completely different thing. You shall check not only how fast ADC sample your input but how often those samples are sent to your software! Again I highly doubt temperature monitor application will update reading 50000 times per second. Try to set 0.1 Hz on your function generator and check graph you are getting in result. Try to add timer to your host software and count samples per sec it receive.

p.s. Oscilloscope with 0.5Hz bandwidth... cool :)

Sir,

i changed my input to 0.1 Hz. now the output gets improved compared to previous result. thanks for this.see below

please look at the Red 1 area, it looks like a good result that i want. here the hyperterminal values are 1.58768, 1.62324, 1.784673.

But in the Red 2 Area, i dont want this result. here the hyperterminal values are as follows

1.56263

0.32455

1.48643

0.17462

1.32344

0.17385

for every value, the intermediate value are coming( green coloured values). i dont want the green coloured values. i want only 1.56, 1.48, 1.32

why is it coming?

here should i consider the synchronisation ?

Your "sine" is clipped. It seems that your ADC is getting not only positive but also negative voltage input. You need to set DC offset for your generator like 1V and let it output +/- 1V AC signal resulting voltages in range 0 upto 2V.

johnson kennady said:

i dont want the green coloured values.

Obviously :) Debug your application and find out where those wrong values come from. At the moment nobody can tell you because not enough info.

Are you sure you read ADC data register right after conversion - every time? And there's no reads before conversion is finished? I suggest to use ADC in IRQ mode, save reading in global volatile variable, send contents of this variable to host application.

yes i am using IRQ mode. no problem in Microcontroller program. Problem in VB program.  i received unwanted special characters like !@#$%^&* etc leads to error in output signal. now i  made a program to filter out the special characters. now i got 90% of output

look below

Thank for your great Help sir

johnson kennady said:

i received unwanted special characters like !@#$%^&* etc leads to error in output signal.

These characters are coming through serial port.  looks good when i checked my output in Hyperterminal the output is in four digits (0046, 0048, 0059 etc...) . In VB.net i import  that ADC output through Serial port to Listbox. here i received 1 digit, 2 digit and 3 digit  which they are error values. i need only 4 digits. so it has to be filtered out.

if you look at the numbers below  without bordered that looks like sine waveform

Bordered Numbers are error values needs to be filtered out (1 digit , 2 digit value and 3 digit values)

Error Values are from special characters like   !@#$%^&*()_+?<> and so on

Decreasing     

1.10459433040078              

0.603616813294233             /// ASCII code 246(3 digit value) . special character is ;

1.0019550342131

0.0342130987292278                  //// Ascii code 14 (2 digit Value). Special characters shift out

 0.00733137829912024

0.679374389051808

0.613391984359726

0.0513196480938416

0.466764418377322

0.354349951124145

0.32258064516129

0.0439882697947214

0.254154447702835

0.0171065493646139

Increasing

0.285923753665689

0.351906158357771

0.403225806451613

0.444770283479961

0.0146627565982405

0.618279569892473

0.681818181818182

0.0171065493646139

0.935972629521017

1.00928641251222

1.06060606060606

0.0122189638318671

1.18279569892473

0.0122189638318671

1.27321603128055

0.0195503421309873

1.29521016617791

As I said - debug and find where those wrong numbers are coming from. Is is ADC or just math error - hard to say. Because not enough info.

Main question - does raw ADC output also have such "wrong" measurements?

johnson kennady said:

looks good when i checked my output in Hyperterminal the output is in four digits (0046, 0048, 0059 etc...) . In VB.net i import  that ADC output through Serial port to Listbox. here i received 1 digit, 2 digit and 3 digit  which they are error values. i need only 4 digits. so it has to be filtered out.

I assume, your digits are litteral digits, consisting of four ASCII number digits.

It's possible that your VB listbox automatically interprets some of them as double-byte characters due to some weird automatic conversion.

'0064' converts to '@' (test: hold down ALT and type '0064' on the num pad). This auto-conversion might be triggered by the leading zero. Actually, Windows too often automatically does unexpected things and you have to run circles to make it stop.

Ilmars said:

As I said - debug and find where those wrong numbers are coming from. Is is ADC or just math error - hard to say. Because not enough info.

Main question - does raw ADC output also have such "wrong" measurements?

The error from only in VB not ADC. ADC works perfect

Ilmars said:

 does raw ADC output also have such "wrong" measurements?

I used to level shift the input analog signal (making bipolar input to single polar)

finally i got output. look below

johnson kennady said:

my first four digits(XXXX)  were only changing. but not YYYY. why it happened?

Debug it :)

Good news. Now i got output. My YYYY digit keep oscillating as XXXX. I changed my microcontroller program

for channel 1

ADC10CTL1 = INCH_1 + ADC10DIV_7 + CONSEQ_3;  

for channel 2

ADC10CTL1 = INCH_1 + ADC10DIV_6 + CONSEQ_3;  

now i go for VB Program for 2 channel Oscilloscope.  illmars sir ,  thanks for supporting.

johnson kennady said:

ADC10CTL1 = INCH_1 + ADC10DIV_6 + CONSEQ_3;  

First, the ADC10 requires a clock frequency of 0.45 to 6.3MHz. With ADC10DIV_x you divide the selected clock (ADC10OSC by default, which is 3.7..6.3MHz). As long as this doesn't move the resulting frequency outside the allowed range, this shouldn't have any influence on the conversion.

Of course, the clock has an influence on the sampling time. A high sampling time results in a low-pass filtered input signal. But not too much. A too-short sampling time may lead to incorrect results, especially if the signal source is high-impedance.
Nevertheless, the sampling time should be selected using the ADC10SHT_x bits.

I'm surprised that you use CONSEQ_3. It means you convert a repeates sequence of channels. So the ADC10 wil convert INCH_1, then INCH_0, then INCH_1 then INCH_0. But you only use one conversion result (maybe the first - if you read if quick enough.

My suggestion: use ADC10DIV_1 or _2, maybe set ADC10SHT_1 or _2 for a higher sampling time. Then use CONSEQ_0 for one single conversion. And change INCH_x to convert exactly the channel you want.

I think you current success is pure coincidence by matching the converison tiem with the code execution time, so you'll get the 'right' result in time. Any change in your code will likely break this again.

Jens-Michael Gross said:

I think you current success is pure coincidence by matching the converison tiem with the code execution time, so you'll get the 'right' result in time. Any change in your code will likely break this again.

Yes, In microcontroller program , i set my timer in millisecond. so that the hyperterminal displays data for every 1millisecond.  my application is to sample both 2 channels at the same time. here my channel 1(first four digit XXXX) and channel 2(Next four digit YYYY) are oscillating.

Sir , Please clarify me that my approaching is right?

01310136
01280133
01280131
01340137
01520151
01780178
01850187
01870193
01840190
01710176
01660171
01610164
01570163
01550159
01560159
01560161
01660168
01970198
02190222
02250228
02270231
02090214
02060212
01900195
01950199
01880193
01890195
01890193
01930196
02010203
02230223
02480249
02520255
02680273
02560259
02540262
02400246
02420247
02320237
02320235
02290234
02320236
02340239
02420243
02640263
02730275
02880288
02810285
02700274
02660270
02660270
02680272
02690273
02710275
02730277
02780282
02800283
02850292

Jens-Michael Gross said:

My suggestion: use ADC10DIV_1 or _2, maybe set ADC10SHT_1 or _2 for a higher sampling time. Then use CONSEQ_0 for one single conversion. And change INCH_x to convert exactly the channel you want.

As your suggest i changed what you mentioned. No difference in the output . just same output as what i got in previous settings(ie:  (ADC10DIV_6 and CONSEQ_3)

Here is my output

08460846
08530854
08340836
08360836
08130816
08150817
07910794
07880790
07670767
07930789
08170814
08230824
08330832
08200823
08260828
08110812
08120813
07930794
07890792
07740775
07590760
07530751
07690766
07850783
07880788
07940792
07810780
07780780
07640765
07520755
07370738
07220724
07020703
06860689
06860683
07170716
07320726
07390738
07440744
07260728
07250727
06980701
06950696
06670669
06670667
06420644
06400640
06530651
06750673
06930692
06900689
06970698
06780681
06800680
06630664
06560659
06360639
06280629
06060606
05900591
05990595
06160614
06370635
06370638
06420641
06250627
06160619
05960600
05800582
05630565
05520554
05350537
05290530
05470544
05710572
05840583
05840582
05860589
05670567
05610566
05420544
05350537
05110515
05090509
04820483
04880485
05080504
05260526
05430541
05340533
05380540
05210522
05210522
05030506
05020501
04790482
04740477
04590458
04710469
04890490
04890488
04950495
04840483
04860486
04660468
04650467
04490451
04380439
04150419
04010402
03940390
04170413
04280425
04320430
04400438
04250423
04220425
03980400
03900390
03610364
03480351
03130316
03080307
03060304
03260325
03460344
03530349
03620360
03440347
03380340
03120313
03100312
02920294
02860289
02630265
02570260
02490246
02650263
02900285
02990299
03160315
03090310
03020304
02800282
02660270
02430245
02270230
02060206
01910193
01900190
02170212
02360236
02480250
02560255
02470250
02380238
02160219
02080209
01890191
01790181
01550158
01470150
01430140
01710167
01910186
02050203
02190219
02140214
02100212
01890190
01910193
01720172
01680170
01450147
01530154
01620161
01880187
02120209
02100208
02200219
02060206
02070205
01870188
01820185
01670171
01520155
01360136
01310129
01440140
01660161