Need advice for creating nS time delay

[Acetronics2]

Hi, Sayzer

Hmmmm, 10 µm center bandpass ... that's a human motion detector !!!

Did you ask for the application Kit from Perkin-Elmer ???

http://optoelectronics.perkinelmer.c...pyroappkit.pdf


By the way ...

having a closer look to your datasheet ... it appears ( to me ... LOL )

1) you must wait for the sensor's output HIGH level ( PIC as input : Hi Z state ...)

2) When pic ready, generate a LOW 200ns MINIMUM pulse, then a HIGH 200 ns MINIMUM pulse

3) Pic as Input for 1µS MINIMUM ( Hi - Z ! ) then reads level


4) generate 200ns MINI low pulse , then 200 ns MINI high pulse ... etc, etc : we're back to step 2)

that repeated for the 15 bits ...

No "hyper high speed" processor required here as 200ns and 1µs are MINIMA ... ( the data is read at the speed given by the low to high transitions sent by the processor

so, try 24µs instead of 200ns and 24µS instead of 1µs waiting ... ( it's the pauseus minimum @ 4 Mhz ...)
after that you will be able to speed it up a bit using @nop !!!




Alain

[sayzer]

Hi, Sayzer

Hmmmm, 10 µm center bandpass ... that's a human motion detector !!!

Did you ask for the application Kit from Perkin-Elmer ???

http://optoelectronics.perkinelmer.c...pyroappkit.pdf

Alain

When I run the circuit on F877 with 20Mhz, I get very good results.
So I have no problem with the circuit; communication etc.

[Acetronics2]

Haaaaaa,

good news !!! you've got it working ...

now, from the datasheet it appears the sensor outputs a new "ready" signal every 2.84 ms ...

do you use polling or interrupting to initiate your reading sequence ???

Alain

[sayzer]

Alain,

I already got it working weeks ago.

The issue is that I need to make it work at 4Mhz.

For new sampling, I am giving it more then it needs. (it needs 3.7mS, I give it 10mS).

BTW; I added Application note; sampling example to my post above.

[Ioannis]

Hi Sayzer.

As Alain said and after looking at the datasheets, there is no need for hyper speed controller. What the DS states, are the minimum pulse width that you are allowed to apply. So, in case you have an extra-super-duper-high-speed controller capable to output 1ps pulses the sensor won't be able to follow.

You can just apply the pulses as fast as possible for the unique reason, to get your data soon. Otherwise there is no need to hurry.

As I understood the procedure:

1. MCU applies a high pulse for at least 200ns

2. MCU enter Z-state and sensor understands that MCU will read now the data

3. Sensor outputs the data bit

4. MCU reads the data bit

5. MCU outputs new high pulse

etc...

All you have to do is repeat the cycle as fast as possible if you want "real time" surveilance.

Ioannis


Ioannis

[sayzer]

Ok;

Thanks Alain and Ioannis.

Since the circuit worked very well at 20Mhz, I thought I was holding the sensor too long at 4Mhz. I must be having some other simple issue based on what you two have said.

I will work on this direction.

[Acetronics2]

Hi, Ioannis

The problem here is the sensor "1" level lasts only 1µS ....

the only solution I see here is use an asm part to generate the high state and test the pin as soon as end of high state .

If i remember ... it's the trick used to test if a pin is low, high or Hi-Z ... !!!

( thanks for the last picture, Sayzer ...)

Alain

[Ioannis]

Where is this 1µs? Did I missed it?

As I understood, the sensor will respond only when the MC enters Z-state.

Ioannis

P.S. Oh I got it. But Alain, this is settling time, not bit width time.

[Ingvar]

My guess is that this code will work......

@ device  pic12F675, protect_off, mclr_off

define OSC 4
DEFINE OSCCAL_1K 1	            'Set OSCCAL for 1K device

DataPin     VAR GPIO.0              'DOCI on the PIR
PIRdata     VAR WORD                
i           VAR BYTE

ANSEL = 0                           'No AD on 12F675
CMCON = %00010111                   'Digital pins - no comparator
WPU = 0                             'No pullups

WHILE 1                             'Do forever
    HIGH GPIO.1                     'Set a pin to time the reading
    GOSUB ReadPIR                   'Call the Sub
    LOW GPIO.1                      'Reset a pin to time the reading
    PAUSE 10                        'Just something to sync the scope
WEND
   

ReadPIR:
    INPUT DataPin                   'Let PIR control the Datapin
    PIRdata = 0                     'Use this time to let Datapin settle
    WHILE DataPin = 0 : WEND        'Wait for PIR to indicate "new data"
    PAUSEUS 25                      'Wait for PIR to fiddle with the data
    FOR i = 14 to 0 STEP -1         'Loop to get 15bits
        LOW DataPin                 'Force Datapin Low
        HIGH Datapin                'Force Datapin High
        INPUT Datapin               'Let PIR control the Datapin
' You may need a short pause here if you have long wires to the PIR    
        PIRdata.0(i) = Datapin      'Sample the datapin
    NEXT
    LOW DataPin                     'Force Datapin Low
    INPUT Datapin                   'Let PIR control the Datapin
    RETURN
    
END

... it compiles and runs as expected. Only problem is that i don't have a PIR to verify it with, it does however look OK on a scope. If i have interpreted the datasheet correctly you should be flying.

/Ingvar