alternatives for 555
Archiver
Posts: 46,084
hello all,
I've read here that the 555 is very sensitive for temperature, what
alternatives do i have to create a square wave of 38 khz that is
stable for the temperature, beside the 555. I do not want to use the
bs2 for this purpose.
I've read here that the 555 is very sensitive for temperature, what
alternatives do i have to create a square wave of 38 khz that is
stable for the temperature, beside the 555. I do not want to use the
bs2 for this purpose.
Comments
That's a myth. The data sheet for National's LMC555, ferinstance, gives
typical timing sensitivity to temperature as 75ppm/degree C (over -40 to
+85 degrees C). It's never going to be as stable as a crystal oscillator,
but it's often adequate if you use a stable capacitor (e.g. COG ceramic,
mica, polystyrene).
>I've read here that the 555 is very sensitive for temperature, what
>alternatives do i have to create a square wave of 38 khz that is
>stable for the temperature, beside the 555. I do not want to use the
>bs2 for this purpose.
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!
(From Rodney Radford)
A circuit that I have used before is based on the CD4060 (14stage
binary counter) and a 640Khz ceramic
resonator. The CD4060 is basically an oscillator and a ripple counter
to divide the 640khz down to something
more usable.
Here is the pinout of the CD4060 (frequencies are assuming a 640khz
input signal into pins 10/11/12 - circuit
shown below):
+-\/-+
160hz 1 | | 16 Vcc
80hz 2 | | 15 625hz
40hz 3 | | 14 2.5khz
10khz 4 | | 13 125hz
20khz 5 | | 12 \
5khz 6 | | 11 >---- see sub-circuit below
40khz 7 | | 10 /
GND 8 | | 9 NC
+----+
Sub-circuit for a 640khz ceramic resonator:
12 >
+
740pf | (you may be able to obtain
11 >
+----+---|(----+ a resonator with builtin
| | | capacitors and three leads)
640khz --- \ |
res. O / 1Mohm |
--- \ |
| | |
10 >
+----+---|(----+
740pf |
GND >
+
A nice part about this circuit is that it delivers a STABLE 40khz
signal, as well as delivering several other
frequencies that can be used to modulate the 40khz carrier. For
example, the person that designed this
circuit (Ken Boone, member of Triangle Amateur Robotics) used it to
build several beacons in his yard to serve
as navigation points for a robotic lawnmower. By diode-OR'ing the
results of the 40khz carrier and one of the
lower frequencies (such as the 125Hz) line to drive a ring of IR-LEDs,
he could locate the beacon and tell
which, of several, beacons he had found.
This circuit has proven to be VERY stable, and is fairly inexpensive
(about $1.50 for the CD4060 and 640Khz
ceramic resonator).
Mike Hardwick wrote:
>
> PJ,
>
> That's a myth. The data sheet for National's LMC555, ferinstance, gives
> typical timing sensitivity to temperature as 75ppm/degree C (over -40 to
> +85 degrees C). It's never going to be as stable as a crystal oscillator,
> but it's often adequate if you use a stable capacitor (e.g. COG ceramic,
> mica, polystyrene).
>
> >I've read here that the 555 is very sensitive for temperature, what
> >alternatives do i have to create a square wave of 38 khz that is
> >stable for the temperature, beside the 555. I do not want to use the
> >bs2 for this purpose.
>
> Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
> Manufacturer of the famous BOB-II Serial Video Text Display Module!
>hello all,
>
>I've read here that the 555 is very sensitive for temperature, what
>alternatives do i have to create a square wave of 38 khz that is
>stable for the temperature, beside the 555. I do not want to use the
>bs2 for this purpose.
The 555 is actually quite stable with temperature! You must take care to
use good quality capacitor and resistors. People run into temperature
stability problems with they toss a low grade ceramic cap in the timing
network - high K capacitors such as the Z5U series have horrible
temperature drift. Use a foil cap of some sort: polystyrene or polypropylene.
dwayne
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 16 years of Engineering Innovation (1984 - 2000)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.