IR and pulsin

Community General Discussions
1

After some time of idleness i got to work again on my IR setup. I still have some problem understanding what happens.

This is my setup:

Transmitter: picaxe28x1, IR led (tsal6100)with cathode connected to pwm (%50 duty, 38000Hz), anode to an output pin.

Code:

pwm bla bla (set up of pwm)

pause 500

pulsout 7, 250

Receiver: picaxe28a, IR receiver and demodulator (tsop1238) properly connected.

Code:

debug

main:

pulsin INPUT_PIN, 0, w0

goto main

-----

I get strange result every time i switch the transmitter on.

Sometimes the results i get are more than one and i don't understand why (i switch on the transmitter, and on the debug appear 2 or 3 different values like 249, which is approximately correct, then 169(?) and sometimes also something close to 30).

Some other times i just get incorrect values like 169 instead 0f 240. I don't really know what is going on. If i understood well, having a 0 in the "state" field of the pulsin command tells it to begin counting only when a high to low transition occurs (that is, when the receiver sees IR modulated at 38kHz), so if i switch on my transmitter this transition only occurs once. But then why do i get more than one rresult? And why do i sometimes get incorrect ones?

strange...(for me)

2

looking at

looking at http://pdf.chinaicmart.com/TSO/TSOP1238.pdf i noticed:
1. burst length should be 10 cycle bursts or longer
2. after each burst which is between 10 and 70 cycles a gap time of 14 cycles is necessary
3. for each burst which is longer than 1.8 ms a corresponding gap time is necessary at
some time in the data stream. This gap should be at leas 4 time longer than the burst

seems like a lot of rules to follow - how exactly are you doing the modulation?

i’ve never programmed a picax - so what does “pulsout 7, 250” do? I’m guessin this is how
your doing the modulation? Is it pin 7 - 250 times at some fixed rate? Could you be
breaking one of the aforementioned rules?

3

actually i never thought

actually i never thought about following those rules! (i know…i’m dumb)

the pulsout commands actually sends a high pulse (=V+) to pin 7(standard output pin) of 2.5ms. The pwm command defines the modulation, and it is at 38000Hz and 50% duty cycle. The puslin in the receiver code should measure this pulse of 2.5ms lenght. I don’t think i have problems with modulation, because i already made a simple program which flashes a led whenever the IR receiver detects any kind of IR light at 38kHz, which is when the output pin of the receiver goes low (it is high by default).

I don’t really know if i understood the meaning of burst and cycle though. Or well, i thought i knew them but i can’t really understand what it means written in that way. Could you help? (I thought a burst was delivering a whole sequence of IR light. But i don’t have many ideas about what a cycle is)

4

even more doubts

this is what i just tried

CODE:

pulsin 0,0,w0

high 0

—

Now, this is what happens when i launch the code: output 0 goes high without me doing anything. How come?

This is the what the pulsin command does:

pulsin

Syntax:

PULSIN pin,state,wordvariable

- Pin is a variable/constant (0-7) which specifies the i/o pin to use.

- State is a variable/constant (0 or 1) which specifies which edge must occur

before beginning the measurement in 10us units (4MHz resonator).

- Wordvariable receives the result (1-65535). If timeout occurs (0.65536s) the

result will be 0.

Function:

Measure the length of an input pulse.

Information:

The pulsin command measures the length of a pulse. In no pulse occurs in the

timeout period, the result will be 0. If state = 1 then a low to high transistion

starts the timing, if state = 0 a high to low transistion starts the timing.

Use the count command to count the number of pulses with a specified time

period.

—

Now, i am not making input 0 (pulsin input) go from high to low in any way (i even trying putting 2 or more pulsins in the code but nothing changes). What i noticed though is that the more pulsins i put, the more time i have to wait before seeing the led light up. But still, should the program stop untile input 0 goes from high to low? ahhhh this thing is making me go mad.

So the thing here is: the timeout is on even if the timing of the incoming pulse hasn’t started. But still this won’t add up with the previous code…hmm ( the one in the previous posts i mean)