Analog issue

[jmgelba]

DT - Thanks, that fixed the issue.
Now, an unexpected one has appeared. First I'll explain the product.
We are looking for a 1 to 2ms pulse appearing on either porta.0 or porta.1. Upon receipt of the pulse I have to send out a 1, 2, 4 or 8ms pulse to turn on 2 FETs located at portb.0 and portb.1 The time of the pulse depends upon dipswitch settings.
So if set to 4ms, the program should scan the capacitors for the correct voltage, wait for a pulse input, fire FET's for 4ms when received, go back and wait for the next pulse in.

The problem is the FETS fire anywhere from 1 time to 6 times per one 1 ms pulse input.
I need an ultra fast reaction time so after a pulse is recieved I cant go and do other stuff before turning on the FET's.

I thought about adding a 10ms delay at the end of the flash subroutine and I've thought about adding a count. If count = 1 and there is a pulse received, I could tell it to ignore the input. The count would have to get to reset to zero in the loop somewhere.

Heres the code as it stands right now.

OSCCON = $70 'set internal resonator to 8mhz
Define  ADC_BITS        10     	' Set number of bits in result
Define  ADC_CLOCK       5     	' Set clock source (3=rc)
Define  ADC_SAMPLEUS    20    	' Set sampling time in uS
DEFINE OSC 8
BNK1 VAR WORD
BNK2 VAR WORD
DUR VAR WORD


ADCON0 = %00000001
ADCON1 = %01111100
ADCON2 = %10111110

TRISA = %11111111
TRISB = %11110000

PORTB.0 = 1
PORTB.1 = 1
PORTB.2 = 1
PORTB.3 = 0

BNK1 = 0
BNK2 = 0
DUR = 0

MAIN:
DUR = 0
PORTB.3 = 0
BNK1 = 0
BNK2 = 0
ADCIN 0, BNK1
ADCIN 1, BNK2

IF PORTB.4 = 1 then
DUR = 8
endif
IF PORTB.5 = 1 THEN 
DUR = 4
endif
IF PORTB.6 = 1 THEN 
DUR = 2
endif
IF PORTB.7 = 1 THEN 
DUR = 1
endif
IF (BNK1 => 466) OR (BNK2 => 466) THEN FLASH
goto MAIN




FLASH:
IF PORTA.4 = 1 OR PORTA.5 = 0 THEN 
PORTB.0 = 0 : PORTB.1 = 0 : PORTB.3 = 1
endif


IF DUR = 1 THEN 
PAUSE 1
endif
IF DUR = 2 THEN 
PAUSE 2
endif
IF DUR = 4 THEN 
PAUSE 4
endif
IF DUR = 8 THEN 
PAUSE 8
endif
PORTB.0 = 1 : PORTB.1 = 1 : PORTB.3 = 0

GOTO MAIN

[Acetronics2]

Hi, JM

That looks to be dealing with high voltage ... and very high instant currents.

May be also a switching up converter to think to ...


soooo ...

are you REALLY sure there's no spike on either an ADC input or 5v supply rails ???

could we have a piece of scheme showing the Fet's drive and the ADC inputs ???

Alain

[jmgelba]

There could be spikes - I have yet to measure for that. And yes, we are switching 2 channels, both at 760W each. 24v at 31.6 Amps.

I'd have to ask the whole forum to sign an NDA to show you the schematic, but the 5v line has a lot of capacitance but the inputs do not as I cant wait for the line to charge. From input pulse to output on needs to be less than 35uS. My customer wanted 5uS or less originally!!

[Archangel]

My customer wanted 5uS or less originally!!

Make it so . . http://www.realmagicwands.com/

[jmgelba]

Just measured for spikes - there are some small ones on the 5v line lasting in the uS range. Largest I've seen was 0.341V. ADC line is dirty. I'm sampling for 20uS. I'll put a .1uF and a 1nF on there and see what happens.

I put a 10ms delay at the end of the flash subroutine and so far that looks to be working.

[Acetronics2]

Hi,

One thing you easily can do is lock your inputs as soon as Fets fired ... you have the time the capacitors charge for gliches " hiding" ...

I'll search on my HDD ... there's an old Elektor project of a ... discharge capacitor welding machine for NiCads ...

Your application HardW should not be so far from that !!!

Alain

[jmgelba]

Hmm have a problem else where. Just to verify my 10ms delay was working, I increased it to 1000ms. Now the flash (FET's)does not respond to the input. I can send a pulse and nothing happens, then I get lucky some times. Turns out that the program is running and pausing for 1000ms as though there has been a pulse sent.

So the problem I have is it is running through the whole program and not returning to MAIN and waiting for a pulse.

IF (BNK1 => 466) OR (BNK2 => 466) THEN FLASH
goto MAIN

This should make the program jump back to the start of MAIN unless the ADC is 466 or higher, right?

FLASH:
IF PORTA.4 = 1 OR PORTA.5 = 0 THEN 
PORTB.0 = 0 : PORTB.1 = 0 : PORTB.3 = 1
endif


IF DUR = 1 THEN 
PAUSE 1
endif
IF DUR = 2 THEN 
PAUSE 2
endif
IF DUR = 4 THEN 
PAUSE 4
endif
IF DUR = 8 THEN 
PAUSE 8
endif
PORTB.0 = 1 : PORTB.1 = 1 : PORTB.3 = 0
PAUSE 1000
GOTO MAIN

the program is running the FLASH routine without actually sending a pulse out to the FETs unless one of the inputs is triggered. I know this because I can measure the time delay between applying an input signal and waiting for an output.

So my question is, why is there up to a 1 second delay between applying a signal and getting an output?