ne555

Archiver

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?

thanks

pieter-jan
________________________________________________________________________________\
_____
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Archiver

It's not too bad, but a little complex to explain
without pictures.

A great tutorial with good info on the 555 appears at:

http://www.uoguelph.ca/~antoon/gadgets/555.htm

Basically, to connect the 555 in Astable Mode, you need
to:

Connect pin 1 to ground
Connect pin 2 to + Voltage
Connect pin 4 to + Voltage (reset pin)
Connect pin 2 & 6 to the positive side of capacitor C,
with the negative side of capacitor C to ground.
Connect the junction of pins 2 & 6 and positive end of
capacitor C to Resistor R2.
Connect the Other End of Resistor R2 to one end of R1
and pin 7
Connect the other end of R1 to plus voltage.

+ >----/////

---

//////

---

|(

---

>>> GND
R1 | R2 | C
| |
Pin 7 Pins 2 & 6


Frequency = 1/(.693 * C * (R1+ 2 * R2))

Have fun! The 555 is one of the most used chips on the
face of the planet! Long before microprocessors were so
easy and available, many cool designs used the 555!

Regards

Jim Kvochick
WB8AZP@a...
> 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?
>
> thanks
>
> pieter-jan
>
________________________________________________________________________________
> _____
> Get more from the Web. FREE MSN Explorer download : http://explorer.msn.com
>
>
>
>

Archiver

Your entire approach can be radically simplified! Take the 555 and
throw it out! You don't need it! Simply use the "freqout" command
to send a the frequency you want through the device you want (in this
case, an IR emmiter). Check out the new stamps-in-class curriculum
for robotics for a complete explanation.

--- In basicstamps@egroups.com, "Pieter-Jan van Diepen"
<diepenpj@h...> wrote:
> 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?
>
> thanks
>
> pieter-jan
>
______________________________________________________________________
_______________
> Get more from the Web. FREE MSN Explorer download :
http://explorer.msn.com

Archiver

I wouldn't use this if the frequency tolerance is tight, because the
RC circuit is very temperature sensitive, but try:

F=1.44/(R1+2R2)C1

t1 provides hi, width of pulse = .693(R1+R2)C1
t2 is low between pulses, width = .693(R2)C1

on the 555,
R1 is from Vcc to pin 7
R2 is from pin 2 to pin 7
C1 is from pin 2 to ground
pin 1 is grounded
pin 6 is connected to pin 2
Vcc also goes to pins 4 & 8
output is at pin 3

Resulting frequency is not voltage dependent, but will vary with
temp changes. Higher quality capacitors will help stabilize some.

Chris Loiacono

---

Original Message

---

From: Pieter-Jan van Diepen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=d6lKsP6_AaitO8qnu37ju9j2icDjpzmH4M0OCUZg_bQmpMbUTMI_dkyV4Iq_DS0EvhAoo7zO8G8RLhMy]diepenpj@h...[/url
Sent: Wednesday, December 06, 2000 1:16 PM
To: basicstamps@egroups.com
Subject: [noparse][[/noparse]basicstamps] ne555


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?

thanks

pieter-jan
_______________________________________________________________
______________________
Get more from the Web. FREE MSN Explorer download :
http://explorer.msn.com

Archiver

>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.