TSOP1738 versus PNA4602?

[ra68gi]

Bruce,
sorry it was my mistake in copying the code here. my original code did have the goto main at the end. For the convenience of those interested in this code i shall rewrite it here.

Please answer my question as to what happens when the pause is reduced below 50ms.

'RB0 -Transistor base driving IR leds
'RB1-LEFT TSOP 3RD PIN
'RB2-CENTER TSOP 3RD PIN
'RB3-RIGHT TSOP 3RD PIN
'RB6-INDICATION LED FOR LEFT OBJECT DETECTED
'RB5-INDICATION LED FOR CENTER OBJECT DETECTED
'RB4-INDICATION LED FOR RIGHT OBJECT DETECTED
'PIN1 OF TSOP-GND, PIN2-Vss

B0 VAR BYTE
LEFT_COUNT VAR BYTE
CENTER_COUNT VAR BYTE
RIGHT_COUNT VAR BYTE
IR_LEFT VAR BYTE
IR_RIGHT VAR BYTE
IR_CENTER VAR BYTE

TRISB=%00001110
PORTB=0

MAIN:
PAUSE 100
GOSUB SEE
IF IR_LEFT=1 THEN
PORTB.6=1
ELSE
PORTB.6=0
ENDIF
IF IR_CENTER=1 THEN
PORTB.5=1
ELSE
PORTB.5=0
ENDIF
IF IR_RIGHT=1 THEN
PORTB.4=1
ELSE
PORTB.4=0
ENDIF
GOTO MAIN

SEE:
LEFT_COUNT=0
CENTER_COUNT=0
RIGHT_COUNT=0
IR_LEFT=0
IR_CENTER=0
IR_RIGHT=0

FOR B0=0 TO 30
PORTB.0=1 'Switch on the transistor connected to IR leds.
PAUSEUS 290 ' burst time as specified by data sheet
IF PORTB.1=0 THEN 'Read TOSP
LEFT_COUNT=LEFT_COUNT+1
ENDIF
IF PORTB.2=0 THEN
CENTER_COUNT=CENTER_COUNT+1
ENDIF
IF PORTB.3=0 THEN
RIGHT_COUNT=RIGHT_COUNT+1
ENDIF
PORTB.0=0 'Swith off transistor connected to IR leds.
PAUSEUS 390 'time gap between bursts as specified by data sheet.
NEXT B0

IF LEFT_COUNT>=15 THEN 'take average to get flicker free or schmitt trigger
IR_LEFT=1 'like clean output at the output pin RB6
ENDIF

IF CENTER_COUNT>=15 THEN
IR_CENTER=1
ENDIF

IF RIGHT_COUNT>=15 THEN
IR_RIGHT=1
ENDIF
RETURN
Raghunathan.

[Bruce]

Please answer my question as to what happens when the pause is reduced below 50ms.

My guess would be you're violating rule #5 you show above.

When you reduce the pause time between jumps to your carrier generation
routine below 50mS, how many bursts are you sending in 1 second period?

[ra68gi]

Bruce,
Let me do the math here.

Carrier frequency on time= 290us pause time+30us(roughly to read the pins)
That equals-320us
Gap time after each burst=390us

Total time period=320+390=710us
This data stream is looped 31 times using for next,so total time=710*31=22010us=22ms

Number of data burst is 31 bursts per 22ms
so for 1sec its (31/22)*1000 = 1409bursts

am i right Bruce?

That means i should use pause time of more than 22ms to make the circuit function properly.
Raghunathan.

[Bruce]

I would factor in the time from Main & back.

Run it through MPLAB sim with the stopwatch. Set a break point on Main. Single
step down to Main, clear the Stopwatch, and hit run. The time it takes from
Main & back is the time it takes to complete one full loop & emit 31 bursts.

If you're within the timing specs shown in the data sheet, and it's not working
as expected, then it's most likely something else like ambient lighting, circuit
noise, other components, etc, etc,.

A lot of things affect results with IR, and the data sheet is just a guide. Specs
shown in most data sheets are derived under optimum laboratory conditions for the
part under test.

You'll normally need to make adjustments based in your own particular operating
environment, parts used, final design, and a host of other factors.

With 3 IR LED's all being fired at once, and 3 IR detectors, it's possible that
you have enough bleed over to influence all 3 detectors at once. Even when an
object isn't in front of an LED/detector pair.

At any rate, I wouldn't try pushing it right up to the limits in a data sheet, and
expect it to work continuously. If my car can go 160mph max I'm not going to drive
everywhere I go at that speed...;o}