From: "Michael A. Terrell"
Subject: Re: circuit wanted-SQUARE PULSE GENERATOR
Date: Wed, 27 Nov 2002 19:09:27 -0500
Organization: Have you seen my bench? No, really! Where is it?
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References: <1038144646.265208@athprx02> <firstname.lastname@example.org> <1038439345.332719@athprx02>
GEORGE BASILIOU wrote:
> I would like to have a closer look to that circuit.
> The problem is that i cannot cleary see the circuit.
> The best way to cleary see the circuit is to be drawn on an other design
> program and sent to me by email email@example.com.
> At this time,that you drawn the circuit into the message,i see a mass of
> numbers and lines,random arranged and appeared in my pc's screen.....
> Anyway,thank you very much for your help.....
> ? "Winfield Hill" ?????? ??? ??????
> > GEORGE BASILIOU wrote...
> > >
> > > Unfortunately i'm not good in designing Circuits. Has anyone to
> > > suggest me any circuit/page to find a square pulse generator,
> > > variable from 1 to 1000 Hz, with 1 Hz step?
> > > I prefer not using 555. I want the circuit to be accurate.
> > The poor 555 gets so much abuse. What a great little chip, two
> > precision comparators, a flip-flop, a large discharge transistor,
> > serious output driving capability, a trimmable voltage divider.
> > These pieces are an excellent starting point for simple accurate
> > oscillators like George wants. If we choose a CMOS 555 version,
> > like Intersil's ICM7555, we can use low charging currents, like
> > 0.33uA, and get accurate operation even down to 1Hz and below
> > with a 0.1uF film capacitor.
> > While Jesper Hansen's design for the AT90S2313 is appealing, see
> > if the simplicity of a few analog parts can't also be appealing.
> > Here's my design that uses a common 10k-ohm 10-turn pot with a
> > turns-counting dial for precision frequencies from 0 to 1000Hz.
> > The IC1 Q1 circuit creates a charging current I = Vr R2 / (R1 R3),
> > used by the 555 to make a frequency f = I / C Vth = I Vr / 2/3 C
> > Note, we can adjust the 2/3 term to eliminate the capacitor's 5%
> > tolerance error, the resistor values, and Q1's beta error. The
> > 7555's DISCHARGE pin current limits at 40mA and then 20 ohms of
> > internal resistance below 1V, so R4 and C2 provide a fixed 25us
> > time for thoroughly discharging C each cycle.
> > After calibration the frequency is proportional to the setting of
> > the 10-turn pot with its counting-dial indicator from 0 to 1 kHz.
> > 10k 10T pot
> > ,--- R2 --+-------, +5 -- 1.65k -,
> > | __ | | |
> > ,---+--|- \ | R1 1k calibrate
> > | | >--' 15.0k pot <------,
> > R3 ,--|+_/ | | |
> > 10.0k | ,----------+ 4.02k |
> > | | | __ | | 2/3 Vr
> > gnd | '-|- \ |/V Q1 +5 gnd +/-5%
> > | | >--| 2n3906 ___|___________ |
> > +--------|+_/ |\ | | |
> > | IC1 | | CONTROL |--' Vth
> > Vr +5 LT1013 | 6 | |
> > +-----------| THRESHOLD |
> > | 2 | OUT |-----
> > 0 to 1kHz precision +-- R4 -+---| TRIGGER |
> > 555-type oscillator |\ | | |
> > | \____ |_7_| DISCHARGE |
> > 3 R2 C _|_ | |_______________|
> > f = --------- ___ C2_|_ |
> > 2 C R1 R3 film | ___ gnd IC2
> > 0.1uF | 0.001 | ICL7555
> > | |
> > gnd gnd
> > IC1 is powered from +15V, and must be a low-offset-voltage opamp
> > because at 1Hz the current-programming voltage is only 5mV.
> > There's lots more to say about this circuit, but it's that time of
> > the year again; I have to go finish burying the fig tree.
You have to view the message with a fixed width font, like Courier.
Michael A. Terrell