16F877 elapsed time control

Hello everyone,

I am pretty new with Pic Programming . I have to measure the time elapsed between V0-V voltages. I am planning to use a POT as an input and display the time on 2x16 display. I am planning to use 16 F877 .


Any ideas?


Thanks

Berkay

What are the minimum and maximum times you will be needing to measure?

Will you be needing anything else going on at the same time?

Maybe something like

Code:

---

for X = 1 to 255
pause 10
t = t + 1
do whatever, pot
if whatever =  thisorthat then tCalc
next x
tCalc:
display t

---

I know, not real code But an idea for you to try.

So if "t" equals 100 , that would mean about a second has passed.

This is for my master thesis project.

My time range is between 300 - 700 microseconds . Depending on the elapsed time value i will control the valves.

Thanks for your help

how can i start the timer for example when the analog input from the pot is 3 V and stop the timer when it is 5 V ?

thanks

Code:

---

loop:
If pot value => 3V then time
goto loop

time:
for X = 1 to 255
pauseus 10
t = t + 1
do whatever, pot
if pot value =  5V then tCalc
next x
tCalc:
display t
goto time

---

You may want to consider using ADCIN in place of POT.
Notice I changed the example to PAUSEUS.
And someplace around here there is a discussion about code execution time, or just test it to adjust the PAUSEUS.

Thanks for your idea,

One more question. How am i gonna define the voltage. I have added a loop like but it didnt work. What can be the problem ?

ADC_READ:

ADCIN 0, ADCINFO
D=ADCINFO*100/51

timeloop:
if D>3 then
T1CON.0=1
if D>=4 then
T1CON.0=0
endif
ELSE
goto timeloop
endif

First off the ADC needs setup, here is an example.
http://www.microengineeringlabs.com/...pbp/adcin8.bas

Voltage...
Lets say you are using an 8 bit ADC. Voltage reference is VDD and the PIC is running at 5 volts.
There are 256 steps, 0 to 255.
The ADC value of 255 will represent full scale and be 5 volts.
The ADC value of 127 will represent 2.5 volts.
Looking for 3 volts? The ADC vale would be 153.
Want more accuracy? The 10 bit ADC has 1024 steps.

Your loop. After the set up.

Code:

---

loop:       
ADCIN 0, adval                                ' Read channel 0 to adval
IF adval <= 153 then gosub Xlabel    '3 volt and less trigger
IF adval = 255 then gosub Zlabel    '5 volt trigger           
Pause 100                                      ' Wait .1 second
Goto loop                                      ' Do it forever

Xlabel:
'Do something
Return

Zlabel:
'Do someting
Return
End

---

That is the basics.

thanks alot
another newbie question
can i use tmrcon istead of for loop
such as;

Quote:

---

CalcTime var word
Define LCD_DREG PORTC
Define LCD_DBIT 4
Define LCD_RSREG PORTB
Define LCD_RSBIT 0
Define LCD_EREG PORTB
Define LCD_EBIT 2
DEFINE LCD_BITS 4
DEFINE LCD_LINES 2

DEFINE ADC_BITS 10
DEFINE ADC_CLOCK 3
DEFINE ADC_SAMPLEUS 50

TRISA = %11111111 ' Set PORTA to all input
ADCON1 = %00000000 ' Set PORTA analog

ADCINFO VAR BYTE


'================================================= =======================

T1CON.0=0
TMR1H = 0
TMR1L = 0
ADCON1 = 0


ADC_READ:
PAUSE 500

timeloop:
ADCIN 0, ADCINFO
IF ADCINFO => 511 THEN GOSUB STARTTIMER
IF ADCINFO == 980 THEN GOSUB STOPTIMER
PAUSE 100
GOTO timeloop

STARTTIMER:
T1CON.0=1
RETURN

STOPTIMER:
T1CON.0=0
RETURN

GOTO ADC_READ

CLEARWDT
CalcTime.Highbyte=TMR1H
CalcTime.Lowbyte=TMR1L

Loope:
LCDOUT $FE, 1
LCDOUT "t:", CalcTime
Pause 500
Goto loope

GOTO ADC_READ
END

---

euh yeah, but the above will never do something else than reading the ADCs?

What do you want to do exactly?

Quote:

---

Originally Posted by mister_e

euh yeah, but the above will never do something else than reading the ADCs?

What do you want to do exactly?

---

hmm i want it to read the adc s and there will be a voltage change from 2.5 v to 4.8 V my aim is to measure the time elapsed between 4.8 and 2.5 volts and write it to lcd

thanks alot for helping

Any idea of the time range between both voltage?

Looks like a kind of ESR measurement to me :D

Quote:

---

Originally Posted by mister_e

Looks like a kind of ESR measurement to me :D

---

Electron Spin Resonance ?
http://hyperphysics.phy-astr.gsu.edu...ecule/esr.html

;) nope, ESR meter... you know this kind of handy meter to find faulty capacitor?

Quote:

---

Originally Posted by mister_e

;) nope, ESR meter... you know this kind of handy meter to find faulty capacitor?

---

Thought so...
Just being a smart _ _ _ :D

pretty difficult for a rookie guy aha :)

My time range is between 300 - 700 microseconds .

Ok so in theory, you shouldn't have any problem with a 16Bits timer. BUT you'll need to compensate for the ADC sampling time.

What you could also do is to use a comparator interrupt...

Hi mackrackit

i tried this

Quote:

---

Originally Posted by mackrackit

Code:

---

loop:
If pot value => 3V then time
goto loop

time:
for X = 1 to 255
pauseus 10
t = t + 1
do whatever, pot
if pot value =  5V then tCalc
next x
tCalc:
display t
goto time

---

You may want to consider using ADCIN in place of POT.
Notice I changed the example to PAUSEUS.
And someplace around here there is a discussion about code execution time, or just test it to adjust the PAUSEUS.

---

but it doesnt stop counting for a defined voltage once it is triggered it does not stop for the final voltage.

Quote:

---

loop:

adcin 0, adval

If adval => 500 then time
goto loop

time:
for X = 1 to 1023
pauseus 10
t = t + 1
If adval = 1000 then tcalc
next x


tCalc:
LCDOUT $fe, 2,"Time" ,":",DEC t
goto time

---

Once i stop it i ll adjust the pauseus value
Anything missing? any suggestions?

You may want to explore the WHILE-WEND command.