Single IC linear adj. pulse generator

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I need a single IC pulse generator with a range of 1-20 Hz that has a
_linear_ frequency adjustment via a potentiometer. Duty cycle
adjustment via trimpot would be an added advantage.

Can anyone advise where I can find a schematic for this?

As far as I am aware making an LM 7555 linear adjust entails
additional active components. For design reasons, I would prefer not
to do this, or use a dedicated function generator IC, ie. XR 2206,
etc.

Thanks for your response

Peter Nielsen

 

[Jim Thompson]

I need a single IC pulse generator with a range of 1-20 Hz that has a
_linear_ frequency adjustment via a potentiometer. Duty cycle
adjustment via trimpot would be an added advantage.

Can anyone advise where I can find a schematic for this?

As far as I am aware making an LM 7555 linear adjust entails
additional active components. For design reasons, I would prefer not
to do this, or use a dedicated function generator IC, ie. XR 2206,
etc.

Thanks for your response

Peter Nielsen

And *why* is that? Homework problem ?

...Jim Thompson

 

[Ban]

Peter Nielsen wrote...

Peter, I can show you a simple circuit meeting your needs, using
a linear pot and a cmos 555 chip, but it does involve additional
active circuitry (transistor and dual opamp), besides the timer
chip, what's wrong with that? Additional parts can allow for an
independant duty cycle adjustment.

Figure 4.75 of our book, AoE, shows a simple voltage-controlled
oscillator (i.e. frequency linearily from a pot) using a dual
opamp and a transistor. If you replace a resistor with another
pot, you can adjust the duty-cycle along with the frequency.

Thanks,
- Win

Here is a nice and very linear variable duty cycle square wave oscillator,
which will work from less than 0.01Hz to 20Hz, but with proper scaling of
charging current and -capacitor and high speed comparator you can easily
reach 20MHz.
If you want a very linear adjustment, you will have to use a voltage
controlled current source at the frequency input and a buffer at the duty
cycle input.

If you buffer the capacitor voltage you have a *very* linear triangle wave,
suitable for reference use in a delta A/D.

ciao Ban

 

[Ban]

see schematic below, forgot to paste it

Here is a nice and very linear variable duty cycle square wave
oscillator, which will work from less than 0.01Hz to 20Hz, but with
proper scaling of charging current and -capacitor and high speed
comparator you can easily reach 20MHz.
If you want a very linear adjustment, you will have to use a voltage
controlled current source at the frequency input and a buffer at the
duty cycle input.

If you buffer the capacitor voltage you have a *very* linear triangle
wave, suitable for reference use in a delta A/D.

ciao Ban

+-----------------+-------+----------------------o
| .-. .-. 10V
| 1k0| | 1k0| |
| | | | |
| '-' '-'
| | |
| >| |<
| |-+-|
| /| | |\
| +---+ |
| | | rail to rail comparator/opamp
| | +---)-----------------+
| frequency | | | |\ |
.-. | | +-+ +------|-\ |
10k | |<-------+ | | V V | | >--+--#
| | .-. | +-+ | | +-|+/ | out
'-' | | | | +----+ | |/ |
| 100k| | | V V 10u| + | ___ |
+---+ '-' | +-+ ### +-|___|-+
| | | | 1N4148| --- | 10k
| |/ +---+ | | | |
+-| | | | | GND | ___
|> \| | |/ |/ | +-|___|-VCC
| |-+---------| | | 3k3
GND <| |> |> | .-. duty cycle
| | | +->| |
.-. .-. .-. | |100k
1k0| | 1k0| | 1k0| | '-'
| | | | | | | ___
'-' '-' '-' +-|___|-GND
| | | 3k3
GND GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

 

[Fred Bloggs]

I need a single IC pulse generator with a range of 1-20 Hz that has a
_linear_ frequency adjustment via a potentiometer. Duty cycle
adjustment via trimpot would be an added advantage.

A very simple way is shown here- you can use a single supply 15V and
derive the 5V by zener or some other regulation, or you can use a single
5V and use a 2nd 555 and diode voltage tripler to derive ~15V:

View in a fixed-width font such as Courier.




freq adj
15V
| 10k 10k 10k
+--------------/\/\---/\/\---/\/\-----+
| /|\ |
c | ---
\| | gnd
npn|--------------------+
/|
e
| duty adj
\
1.5k 10k 10k 10k
\ +--/\/\---/\/\---/\/\-----+
5V / | /|\ |
o e | | ---
| |/ | | Vth gnd
+-----|pnp | |
| |\ | | 1M
| c | +---/\/\------+
| | | | |
+-------|-----------+----------|---------+ |
| | | | | comparator
| | +--vcc---+ | | |
| I | | +------(+)\ |
| | | 555 | | >--+----> Pulse
| V | | +------(-)/
| | | | |
+----+-----+-thresh | | | 3xI
| | +-trig | | | Frequency= ------
| === +-dis | | | CtxVcc
| CT | | | |
| 47u +-- gnd -+ | |
| | | | | Vth
| +------------+-------------------+ Duty= --- - 1
| | | 1.6
+---------------------------+ ---
| gnd
|
| / / / -3.4-
| / | / | / |
| | / | / | / |
+-> -+------+------+------+-----Vth-
| / | / | / | /
-1.6-

- - - - -5-
| | | | | | | |
| | | | | | | | Pulse
| | | | | | | |
-+ +----+ +----+ +----+ +----0-