IR detector which port? RB0 (int), CCP1 or generic PIC pin? - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 13th March 2007, 05:43 PM

When using a 38KHz IR detector, what type on input pin is your favourite (least software overhead)?

Sceadwian · 14th March 2007, 12:59 AM

An interupt pin set to rising edge, unless you have a problem with noise.

Mike, K8LH · 14th March 2007, 03:14 AM

Good question. And one I've been comtemplating recently.

If you want to decode Sony SIRC 12, 15, and 20 bit codes and you use the CCP "capture" mode timers then how would you know if you're decoding a 12, 15 or 20 bit code? In other words, how would you know when to stop waiting for a new edge interrupt?

It almost seems better to use CCP "compare" interrupts at computed intervals to sample and filter the 2400/550 "start" bit, the 550/550 "0" bit, or the 1100/550 "1" bit and simply clock in 20 bits, though the last several bits may be null for 12 and 15 bit codes.

Is there a better way to come up with a small simple reliable interrupt driven background decoder task?

blueroomelectronics · 14th March 2007, 04:17 AM

I'm using CCP1 (PWM) to run a relay, and tmr1 osc (32KHz) and will lose the CCP2. So I have to use RB0.

Mike, K8LH · 14th March 2007, 09:37 AM

You're using a PWM signal to drive a relay?

blueroomelectronics · 14th March 2007, 01:42 PM

PWM 100% to pull in the relay and 50% or so to keep it engaged.

Mike, K8LH · 14th March 2007, 02:09 PM

That's got to be one of the most exotic uses for PWM I've come across (grin). I've used a resistor in series with a relay to accomplish something similar. When you first key the relay it sees the full voltage and as the current ramps up there's a small voltage drop built up across the resistor. Of course this wastes power on the resistor while your scheme is conserving energy quite nicely.

**Nigel Goodwin** · 14th March 2007, 02:20 PM

Quote:

Originally Posted by Mike, K8LH

That's got to be one of the most exotic uses for PWM I've come across (grin). I've used a resistor in series with a relay to accomplish something similar. When you first key the relay it sees the full voltage and as the current ramps up there's a small voltage drop built up across the resistor. Of course this wastes power on the resistor while your scheme is conserving energy quite nicely.

If you place an electroytic capacitor across the resistor the charging current will provide a full voltage pulse to the relay, then after it's charged the resistor will provide the holding current - fairly standard practice!.

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13th March 2007, 05:43 PM	(permalink)
blueroomelectronics	IR detector which port? RB0 (int), CCP1 or generic PIC pin? When using a 38KHz IR detector, what type on input pin is your favourite (least software overhead)? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

14th March 2007, 12:59 AM	(permalink)
Sceadwian	An interupt pin set to rising edge, unless you have a problem with noise. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

14th March 2007, 03:14 AM	(permalink)
Mike, K8LH	Good question. And one I've been comtemplating recently. If you want to decode Sony SIRC 12, 15, and 20 bit codes and you use the CCP "capture" mode timers then how would you know if you're decoding a 12, 15 or 20 bit code? In other words, how would you know when to stop waiting for a new edge interrupt? It almost seems better to use CCP "compare" interrupts at computed intervals to sample and filter the 2400/550 "start" bit, the 550/550 "0" bit, or the 1100/550 "1" bit and simply clock in 20 bits, though the last several bits may be null for 12 and 15 bit codes. Is there a better way to come up with a small simple reliable interrupt driven background decoder task?

14th March 2007, 04:17 AM	(permalink)
blueroomelectronics	I'm using CCP1 (PWM) to run a relay, and tmr1 osc (32KHz) and will lose the CCP2. So I have to use RB0. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

14th March 2007, 09:37 AM	(permalink)
Mike, K8LH	You're using a PWM signal to drive a relay?

14th March 2007, 01:42 PM	(permalink)
blueroomelectronics	PWM 100% to pull in the relay and 50% or so to keep it engaged. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

14th March 2007, 02:09 PM	(permalink)
Mike, K8LH	That's got to be one of the most exotic uses for PWM I've come across (grin). I've used a resistor in series with a relay to accomplish something similar. When you first key the relay it sees the full voltage and as the current ramps up there's a small voltage drop built up across the resistor. Of course this wastes power on the resistor while your scheme is conserving energy quite nicely. Last edited by Mike, K8LH; 14th March 2007 at 02:14 PM.