sawtooth circuit modeling?

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

This is one of the simplest generator

can't help with the matlab stuff

martin

Google this: matlab spice interface

Many good links will magically appear. Good luck!

-- Joe

kthxbye

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

Good Luck! Rich

Integrate a constant current.

-- Many thanks,

Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss:

Please visit my GURU's LAIR web site at

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:

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

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

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.

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

-- Joe

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

Ugh. 555.

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

Here's another possibility:

-- Joe

Parts Count from Above Link

Parts Count for 555 sawtooth gen

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?

-- Joe

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

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