Fwd: Re: [basicstamps] ne555
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>Reply-To: basicstamps@egroups.com
>Subject: Re: [noparse][[/noparse]basicstamps] ne555
It's been a while since I tried to use a 555 for anything serious (not
since Stamp 1, at least), but as I remember it, you can't get a square wave
from the usual two resistor-one capacitor configuration. The capacitor
charges through two resistors and discharges through only one. I think Don
Lancaster had a trick that used a diode across the pin 6 - pin 7 resistor
that allowed you to make it square, but the frequency tuning would then
require adjusting both resistors. I also recall that I quit using the
standard 555 in favor of the CMOS part (7555 or something like that). And
remember to put a cap on pin 5 for stabilization.
Just my $.02 worth and maybe only worth half of that!
Mike
> >hello,
> >
> >I want to use a 555 timer for a square wave of 38 khz. This wave is to
> drive
> >a ir-led that i use for a ir-sensor, that reacts at 38 khz.
> >
> >What values of r and c should i use?
> >
>
>Geez - three replies and not one answered the question. Try 1.8K for R1, 1k
>for R2 and .01uf for C. Ri connects pin 7 to Vcc, R2 connects pin 7 to 6 & 2.
_________________________________
Mike Walsh
walsh@i...
California Institute of Technology
Biology Electronics Shop
>Subject: Re: [noparse][[/noparse]basicstamps] ne555
It's been a while since I tried to use a 555 for anything serious (not
since Stamp 1, at least), but as I remember it, you can't get a square wave
from the usual two resistor-one capacitor configuration. The capacitor
charges through two resistors and discharges through only one. I think Don
Lancaster had a trick that used a diode across the pin 6 - pin 7 resistor
that allowed you to make it square, but the frequency tuning would then
require adjusting both resistors. I also recall that I quit using the
standard 555 in favor of the CMOS part (7555 or something like that). And
remember to put a cap on pin 5 for stabilization.
Just my $.02 worth and maybe only worth half of that!
Mike
> >hello,
> >
> >I want to use a 555 timer for a square wave of 38 khz. This wave is to
> drive
> >a ir-led that i use for a ir-sensor, that reacts at 38 khz.
> >
> >What values of r and c should i use?
> >
>
>Geez - three replies and not one answered the question. Try 1.8K for R1, 1k
>for R2 and .01uf for C. Ri connects pin 7 to Vcc, R2 connects pin 7 to 6 & 2.
_________________________________
Mike Walsh
walsh@i...
California Institute of Technology
Biology Electronics Shop