Hello everyone,
I want to communicate with my robot via IR, but im having trouble with the
recieving hardware. My first idea was to simply use a phototransistor to
output a voltage relative to the light level, and capacitatively couple
this to an op-amp wired as a comparator. This turned out to be too
insensitive, (maximum range was less than a foot). I do not want to use
the 40KHz modulated sharp modules, as they are too expensive. preferably
the hardware would involve an op-amp, a phototransistor and a few passive
compnents. anyone have any ideas? thanks.
------------------------------------------------------------------------------
A member of the PI-100 Club:
3.1415926535897932384626433832795028841971693993751
058209749445923078164062862089986280348253421170679
Try using an phototransitor hooked up to an active band-pass filter
running into a comparitor. Did the trick for a simple project of my own.
Obviously, using a single chip with several op amps will take very little
real estate.
> Hello everyone,
> I want to communicate with my robot via IR, but im having trouble with the
> recieving hardware. My first idea was to simply use a phototransistor to
> output a voltage relative to the light level, and capacitatively couple
> this to an op-amp wired as a comparator. This turned out to be too
> insensitive, (maximum range was less than a foot). I do not want to use
> the 40KHz modulated sharp modules, as they are too expensive. preferably
> the hardware would involve an op-amp, a phototransistor and a few passive
> compnents. anyone have any ideas? thanks.
>
> ------------------------------------------------------------------------------
> A member of the PI-100 Club:
> 3.1415926535897932384626433832795028841971693993751
> 058209749445923078164062862089986280348253421170679
>
Those Sharp IR detection modules are $3.59 at Radio Shack, and $2.88 from
Digi-Key. Thats got to be less than the components your using to try to get
useful signal from a PIN. They are very nice to use as well. The
automatically compensate for lighting conditions and optimize the reception of
40KHz flashing IR signal. The 40KHz flashing can easily be generated by
another PIC using the TIMR2 PWM program (AN564), my code looks like:
I have used this code on 16C6x and 16C7x chips that have a timer 2. It
generates a constant 40KHz pulse stream. I suspect that you could modulate
this signal by modifying the TRISC,1 bit (input no signal, output 40KHz). May
need and external resistor for this, I have not tried it yet.
I think i know what an active band-pass filter is, it filters out all
signals execpt thoes that are in a range of frequencies. my question is,
does anyone have a schematic for such a circuit? Also, what freqencies did
you allow it to pass? I'd rather not use any modulation (whiuch is what
this sounds like) but if absolutely nessasary, i will.
------------------------------------------------------------------------------
A member of the PI-100 Club:
3.1415926535897932384626433832795028841971693993751
058209749445923078164062862089986280348253421170679
> Try using an phototransitor hooked up to an active band-pass filter
> running into a comparitor. Did the trick for a simple project of my own.
> Obviously, using a single chip with several op amps will take very little
> real estate.
>
> Good luck,
> Vince
>
> On Mon, 1 Feb 1999, Lynx {Glenn Jones} wrote:
>
> > Hello everyone,
> > I want to communicate with my robot via IR, but im having trouble with the
> > recieving hardware. My first idea was to simply use a phototransistor to
> > output a voltage relative to the light level, and capacitatively couple
> > this to an op-amp wired as a comparator. This turned out to be too
> > insensitive, (maximum range was less than a foot). I do not want to use
> > the 40KHz modulated sharp modules, as they are too expensive. preferably
> > the hardware would involve an op-amp, a phototransistor and a few passive
> > compnents. anyone have any ideas? thanks.
> >
> > ----------------------------------------------------------------------------
--
> > A member of the PI-100 Club:
> > 3.1415926535897932384626433832795028841971693993751
> > 058209749445923078164062862089986280348253421170679
> >
>
Well, actually, the components i have are LM324 quad op amps which cost
about $.50 a piece, and IR phototransistors at about $.30 a piece, which
is only $.80, so adding a few resistors, and capacitors, this is much
cheaper... but if all else fails, i may have to resort to the modules.
------------------------------------------------------------------------------
A member of the PI-100 Club:
3.1415926535897932384626433832795028841971693993751
058209749445923078164062862089986280348253421170679
> Those Sharp IR detection modules are $3.59 at Radio Shack, and $2.88 from
> Digi-Key. Thats got to be less than the components your using to try to get
> useful signal from a PIN. They are very nice to use as well. The
> automatically compensate for lighting conditions and optimize the reception of
> 40KHz flashing IR signal. The 40KHz flashing can easily be generated by
> another PIC using the TIMR2 PWM program (AN564), my code looks like:
>
> #define bank0 bcf STATUS,5
> #define bank1 bsf STATUS,5
>
>
> movlw 0x04 ;[00000100] enable timer
> movwf T2CON ;using timer 2
> movlw 0x0C ;[00001100] use PWM mode
> movwf CCP2CON
> movlw .125
> bank1
> movwf PR2 ;period register
> bank0
> movlw .62
> movwf CCPR2L ;pulse width
>
> I have used this code on 16C6x and 16C7x chips that have a timer 2. It
> generates a constant 40KHz pulse stream. I suspect that you could modulate
> this signal by modifying the TRISC,1 bit (input no signal, output 40KHz). May
> need and external resistor for this, I have not tried it yet.
>
> Hope this helps
> Pherd
>
I have to agree with Pherd, below: spend the extra $2 and use the modules.
I've found them to be very reliable and, as he also states, it's pretty
simple to use a PIC in the transmitter to generate the 40KHz modulation.
>Hello!
>
>I want to learn me about the communication between
>IR transmitter and receiver together with a PIC.
>
>Anybody who knows of any good side about that
>on the web?
>
>Regards
>ÅkeN
>____________________________________________
Hi AkeN
I presume you are talking about irDA, Microchip have this chip that will do
the protocol for you the MCP215X. The application notes are very good and if
you are into Visual C++ it tells you how to write applications.
In the process of reading the application notes you will find links to the
irDA standard and other useful info.
Hope it helps
Regards
Luis
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