sawtooth circuit modeling?

dantimatter · Jun 7, 2007

hello all,

i'd like to model a circuit that outputs a sawtooth function. there's
really two things that i'm looking for: 1) a schematic of the simplest
circuit that can produce a sawtooth output, and 2) a way to model it
with something like MATLAB or Mathematica. is anyone here familiar
with any schematic capture circuit analysis packages, particularly
ones that can generate the underlying circuit equations? what i
imagine would be ideal is if i could just plunk together a couple of
resistors, capacitors, and op-amps in a SPICE like program, then get
the equations that describe the circuit, and finally carry those
equations over to MATLAB to model how things change as i vary system
parameters. i'm at a total loss here. does anyone have any
suggestions??

many thanks,
dan

D from BC · Jun 7, 2007

hello all,

i'd like to model a circuit that outputs a sawtooth function. there's
really two things that i'm looking for: 1) a schematic of the simplest
circuit that can produce a sawtooth output, and 2) a way to model it
with something like MATLAB or Mathematica. is anyone here familiar
with any schematic capture circuit analysis packages, particularly
ones that can generate the underlying circuit equations? what i
imagine would be ideal is if i could just plunk together a couple of
resistors, capacitors, and op-amps in a SPICE like program, then get
the equations that describe the circuit, and finally carry those
equations over to MATLAB to model how things change as i vary system
parameters. i'm at a total loss here. does anyone have any
suggestions??

many thanks,
dan

SwitchercadIII from Linear Technology is a free spice program..
A triangle generator can be easily defined in the program.
ex:.pick rise and fall times..

Here's some triangle generator cct. ideas
DAC
Square wave and integrator
bidirection I source and capacitor (hysteretic oscillator)
RC circuit
Sound card
XR2206
There's some bigass chip out there that does wave synthesis (forgot
number)

D from BC

martin · Jun 7, 2007

hello all,

i'd like to model a circuit that outputs a sawtooth function. there's
really two things that i'm looking for: 1) a schematic of the simplest
circuit that can produce a sawtooth output, and 2) a way to model it
with something like MATLAB or Mathematica. is anyone here familiar
with any schematic capture circuit analysis packages, particularly
ones that can generate the underlying circuit equations? what i
imagine would be ideal is if i could just plunk together a couple of
resistors, capacitors, and op-amps in a SPICE like program, then get
the equations that describe the circuit, and finally carry those
equations over to MATLAB to model how things change as i vary system
parameters. i'm at a total loss here. does anyone have any
suggestions??

many thanks,
dan

This is one of the simplest generator
http://www.oberlin.edu/physics/catalog/demonstrations/em/neonosc.html

can't help with the matlab stuff

martin

John Fields · Jun 7, 2007

---
Yes, capitalize the first word of a sentence and the personal
pronoun: 'I'.

J.A. Legris · Jun 7, 2007

hello all,

i'd like to model a circuit that outputs a sawtooth function. there's
really two things that i'm looking for: 1) a schematic of the simplest
circuit that can produce a sawtooth output, and 2) a way to model it
with something like MATLAB or Mathematica. is anyone here familiar
with any schematic capture circuit analysis packages, particularly
ones that can generate the underlying circuit equations? what i
imagine would be ideal is if i could just plunk together a couple of
resistors, capacitors, and op-amps in a SPICE like program, then get
the equations that describe the circuit, and finally carry those
equations over to MATLAB to model how things change as i vary system
parameters. i'm at a total loss here. does anyone have any
suggestions??

many thanks,
dan

Google this:
matlab spice interface

Many good links will magically appear. Good luck!

martin · Jun 7, 2007

kthxbye

Rich Grise · Jun 7, 2007

does anyone have any suggestions??

Go take the course again, from the beginning, but pay attention this time.

Good Luck!
Rich

Don Lancaster · Jun 8, 2007

Integrate a constant current.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

MooseFET · Jun 8, 2007

hello all,

i'd like to model a circuit that outputs a sawtooth function. there's
really two things that i'm looking for: 1) a schematic of the simplest
circuit that can produce a sawtooth output, and 2) a way to model it
with something like MATLAB or Mathematica.

Why? LTSpice does everything needed so why bring less well suited
software into the picture?

"simplest" has many meansing. Here's a bit of ASCII art:

+V ----/\/\/---------+------+----- Output
! !
--- DEVICE
--- !
! !
GND GND

DEVICE can be a NE-2 a DIAC, an SCR, ... and etc.

dantimatter · Jun 8, 2007

thanks to all for the quick responses. i'd like to use MATLAB i'm
teaching half-of-a-course on systems biology, and the laboratory
component consists of a bank of computers loaded with MATLAB and
Mathematica. the machines don't have a circuit simulator. there's a
particular biological oscillator problem that i'd like the students to
think about, but it requires some circuit modeling. if this turns out
to be too difficult to implement or not intsructive, i'll just drop
this particular problem from the class.

dan

dantimatter · Jun 8, 2007

and before 'john fields' gets all preachy, there should be a 'because'
between 'MATLAB' and 'i'm' in the second sentence, and instructive
should be spelled 'instructive'.
dan

Don Lancaster · Jun 8, 2007

MooseFET said:
Why? LTSpice does everything needed so why bring less well suited
software into the picture?

"simplest" has many meansing. Here's a bit of ASCII art:

+V ----/\/\/---------+------+----- Output
! !
--- DEVICE
--- !
! !
GND GND

DEVICE can be a NE-2 a DIAC, an SCR, ... and etc.

Your "bit of ASCII art" is only capable of generating a sawtooth
waveform with an infinite input voltage.

It instead generates an exponantial waveform.

The best way to generate a sawtooth is to integrate a constant current.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

J.A. Legris · Jun 8, 2007

thanks to all for the quick responses. i'd like to use MATLAB i'm
teaching half-of-a-course on systems biology, and the laboratory
component consists of a bank of computers loaded with MATLAB and
Mathematica. the machines don't have a circuit simulator. there's a
particular biological oscillator problem that i'd like the students to
think about, but it requires some circuit modeling. if this turns out
to be too difficult to implement or not intsructive, i'll just drop
this particular problem from the class.

dan

I suggest that you post the actual biological problem here - you just
might get lucky.

dantimatter · Jun 9, 2007

I suggest that you post the actual biological problem here - you just
might get lucky.

the data's not published just yet, so i'm reluctant to give out too
many details.

it looks like you using an op-amp integrator might do the trick for
the ramping-up, and if i can rig up a switch across the capacitor that
will quickly discharge it once the voltage has reached a certain
value, then i've got my sawtooth. so now i guess the question is: how
do i implement that switch? it's been so long since i've looked at an
electronics textbook; at least 10 years. is there a way to set up
some kind of comparator, so that when the voltage on the output of the
op-amp reaches a certain threshold, the switch is thrown and the
capacitor rapidly discharges, and then is quickly thrown again so the
ramping-up can begin all over again?

many thanks to all!

dan

D from BC · Jun 9, 2007

the data's not published just yet, so i'm reluctant to give out too
many details.

it looks like you using an op-amp integrator might do the trick for
the ramping-up, and if i can rig up a switch across the capacitor that
will quickly discharge it once the voltage has reached a certain
value, then i've got my sawtooth. so now i guess the question is: how
do i implement that switch? it's been so long since i've looked at an
electronics textbook; at least 10 years. is there a way to set up
some kind of comparator, so that when the voltage on the output of the
op-amp reaches a certain threshold, the switch is thrown and the
capacitor rapidly discharges, and then is quickly thrown again so the
ramping-up can begin all over again?

many thanks to all!

dan

Constant current source + 555 timer set up for astable multivibrator
operation.
D from BC

J.A. Legris · Jun 9, 2007

Constant current source + 555 timer set up for astable multivibrator
operation.
D from BC

Ugh. 555.

Notwithstanding, Win Hill provides a circuit on p.290 of AoE, Fig.
5.35.

Here's another possibility:
http://www.interq.or.jp/japan/se-inoue/e_ckt17.htm

D from BC · Jun 9, 2007

Ugh. 555.

Notwithstanding, Win Hill provides a circuit on p.290 of AoE, Fig.
5.35.

Here's another possibility:
http://www.interq.or.jp/japan/se-inoue/e_ckt17.htm

Parts Count from Above Link
1 dual op amp
4 resistors
1 cap
2 diodes
Split supply??!

Parts Count for 555 sawtooth gen
1 LMC555
1 JFET
1 resistor
1 capacitor
Single supply

I don't have the AoE...is fig 5.35 the 555+ Isource cct?
I make this stuff up but later discover how old my idea is..

D from BC

J.A. Legris · Jun 9, 2007

Parts Count from Above Link
1 dual op amp
4 resistors
1 cap
2 diodes
Split supply??!

Parts Count for 555 sawtooth gen
1 LMC555
1 JFET
1 resistor
1 capacitor
Single supply

I don't have the AoE...is fig 5.35 the 555+ Isource cct?
I make this stuff up but later discover how old my idea is..
D from BC

Yes it is. It has more parts that yours but then again, it probably
works! I like the op-amp design because it is more symmetrical. Can
you use the 555 version to make a nice triangle or reverse sawtooth?

D from BC · Jun 9, 2007

Yes it is. It has more parts that yours but then again, it probably
works! I like the op-amp design because it is more symmetrical. Can
you use the 555 version to make a nice triangle or reverse sawtooth?

It's all up to the quality of the current source in the 555 cct..
I don't know the fine bugs of a JFET I source used in this app..

Yes triangle can be formed too..The 555 would need to control a
sink/source Iregulator.

Reverse sawtooth can be done with inversion to regular sawtooth.
D from BC

Jasen · Jun 9, 2007

hello all,

i'd like to model a circuit that outputs a sawtooth function. there's
really two things that i'm looking for: 1) a schematic of the simplest
circuit that can produce a sawtooth output, and 2) a way to model it
with something like MATLAB or Mathematica. is anyone here familiar
with any schematic capture circuit analysis packages, particularly
ones that can generate the underlying circuit equations? what i
imagine would be ideal is if i could just plunk together a couple of
resistors, capacitors, and op-amps in a SPICE like program, then get
the equations that describe the circuit, and finally carry those
equations over to MATLAB to model how things change as i vary system
parameters. i'm at a total loss here. does anyone have any
suggestions??

a square wave fed to a R-C low-pass filter.

that's basically a logarythmic decay curve in both directions.

and similar to what you'd find on pin 2 of a 555 based astable oscilator.

Bye.
Jasen

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