RA4 input or output?

fuzzy · Joined: 26 Feb 2005 Posts: 64

Hi, i configured pic16f627A PIN RA4 as output to control a NPN transistor to control 2 led raws. I've some problem programming it.

Using Output_high(pin A4) led flashes for a bit and then shut down.
if i put Output_high(pin A4) in infinite cycle, led flashes but only if in firmware i try to control anyother Port A PIN.

I currently PullUp RA4 with a 10K resistor.

Is there any way to solve this problem?

Do you think it's better to use A4 as In put or OUTPUT do I need to change my pin's configuration and use a push pull pin to control a NPN transistor??

Thanks

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

This post talks about your problem in detail:
http://www.ccsinfo.com/forum/viewtopic.php?t=27227

fuzzy · Joined: 26 Feb 2005 Posts: 64

I had already read that tread.
I was also wondering which is the best use for RA4, input or output?
I'm using a transistor to drive led, so pin not directly on led. Is there a way to solve this problem??

I also put a PIC16F88 on my circuit that has got a push-pull RA4. It works better but I hear a whisper when i press key that is in RA1 and RA3.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

But what about the series resistor described in that thread ?

Describe your external circuit completely.

fuzzy · Joined: 26 Feb 2005 Posts: 64

My circuit is:5V 10K pullup to RA4, from it a series 2,2kohm resistor to NPN Base, NPN Emitter to GND and Collector to led katode. 2 or more led columns from 5V. it's simple. Ra4 doesn't reach 0.8VDD, this is the reason I think. But why i've got a whisper if using 16F88?

I also Use Ra0 as direct led Driver. and ra1, ra2,ra3 as input.

could you sugest me a better configuration?? Thanks

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I don't know what you mean by a "whisper". You said it's connected
to some LEDs. Apparently you have some audio device connected to
other pins. It could be a read-modify-write problem. Here's a long
thread on that:
http://www.ccsinfo.com/forum/viewtopic.php?t=21825&highlight=16f88+rmw

If you're having trouble with pin RA4 as an output, and you still the
option of using other pins, then go ahead and use the other pins as
outputs. Use RA4 as an input. It's easier.

fuzzy · Joined: 26 Feb 2005 Posts: 64

whisper as a vibration....... as an audible frequency switching in leds. Their luminosity decreases too in that case.as it is driven by PWM.
not audio device. The same happen with 16F88.

Leds on RA4 have a delay time to power off(about 3 seconds) after key switch. With 16f88 leds decrease luminosity but power off after delay. With 16F627A (and the same program of 16F88) leds power off immediately. i cant keep them on for a little period.

Strange behaviour

I think I'll use it A4 as Input. I hope not to have problems.

Do you think PWM can give some problem to RA port??

PWM out is RB3 for 16f627A

should it be any analog problem??

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Apparently, audible noise in LED arrays is possible if the PWM frequency
is in the normal hearing range. This page suggests using a 30 KHz
PWM frequency to prevent the problem:
http://www.national.com/news/item/0,1735,1085,00.html

The LM3519 data sheet has some additional comments on audible noise
with an LED driver. See the section on PWM dimming:
http://cache.national.com/ds/LM/LM3519.pdf

fuzzy · Joined: 26 Feb 2005 Posts: 64

the problem is that i'm driving leds only on or off. not in PWM. i can't understand why it seems PWM.

Ttelmah · Guest