Hi, anyone have a favorite brand/flavor of lm358 or equivalent opamp to recommend for a simple, low performance integrator to generate a voltage ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to two seconds duration, no repeating..one shot style. Looking at just Mouser, there seem to be 23 parts in soic-8 to choose from... Thanks, Bill Martin
lm358-like opamps
Started by ●March 15, 2012
Reply by ●March 15, 20122012-03-15
On Thu, 15 Mar 2012 16:41:12 -0700, Bill Martin wrote:> Hi, > anyone have a favorite brand/flavor of lm358 or equivalent opamp to > recommend for a simple, low performance integrator to generate a voltage > ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to > two seconds duration, no repeating..one shot style. Looking at just > Mouser, there seem to be 23 parts in soic-8 to choose from...Surely you mean 23000. The LM358 is still out there, and cheap. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
Reply by ●March 15, 20122012-03-15
On 3/15/2012 4:41 PM, Bill Martin wrote:> Hi, > anyone have a favorite brand/flavor of lm358 or equivalent opamp to > recommend for a simple, low performance integrator to generate a voltage > ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to > two seconds duration, no repeating..one shot style. Looking at just > Mouser, there seem to be 23 parts in soic-8 to choose from... > > Thanks, > Bill MartinSince you have no requirements for linearity...or anything else... I'd just use a cap and a resistor. The only application I can think of for a device that has "no repeating" is some kind of trigger for something that goes boom. Precise requirements/specifications are your friend.
Reply by ●March 15, 20122012-03-15
On 03/15/2012 05:10 PM, mike wrote:> On 3/15/2012 4:41 PM, Bill Martin wrote: >> Hi, >> anyone have a favorite brand/flavor of lm358 or equivalent opamp to >> recommend for a simple, low performance integrator to generate a voltage >> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to >> two seconds duration, no repeating..one shot style. Looking at just >> Mouser, there seem to be 23 parts in soic-8 to choose from... >> >> Thanks, >> Bill Martin > > Since you have no requirements for linearity...or anything else... > I'd just use a cap and a resistor.That was version 1.> > The only application I can think of for a device that has "no repeating" > is some kind of trigger for something that goes boom.Oh, I hope not. It just shuts down due to power being turned off. :-)> > Precise requirements/specifications are your friend.Ok, a sort-of-linear ramp is desired. I may then torture that into something exponential, but opposite of how r-c time constant works. The game is simple: Feed as much power to a small dc brushed motor as possible without making the drive "slip". So, the faster it's turning, the more pwm I can shove at it without increasing average current too much. It's a toy circuit...driving a 1/24 scale electric dragster. Bill
Reply by ●March 15, 20122012-03-15
Tim Wescott wrote:> On Thu, 15 Mar 2012 16:41:12 -0700, Bill Martin wrote: > > >>Hi, >>anyone have a favorite brand/flavor of lm358 or equivalent opamp to >>recommend for a simple, low performance integrator to generate a voltage >>ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to >>two seconds duration, no repeating..one shot style. Looking at just >>Mouser, there seem to be 23 parts in soic-8 to choose from... > > > Surely you mean 23000. > > The LM358 is still out there, and cheap. >Ha, you got that right!,. I have crap loads of them. Jamie
Reply by ●March 15, 20122012-03-15
Bill Martin wrote:> On 03/15/2012 05:10 PM, mike wrote: > >> On 3/15/2012 4:41 PM, Bill Martin wrote: >> >>> Hi, >>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to >>> recommend for a simple, low performance integrator to generate a voltage >>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to >>> two seconds duration, no repeating..one shot style. Looking at just >>> Mouser, there seem to be 23 parts in soic-8 to choose from... >>> >>> Thanks, >>> Bill Martin >> >> >> Since you have no requirements for linearity...or anything else... >> I'd just use a cap and a resistor. > > That was version 1. > >> >> The only application I can think of for a device that has "no repeating" >> is some kind of trigger for something that goes boom. > > Oh, I hope not. It just shuts down due to power being turned off. :-) > >> >> Precise requirements/specifications are your friend. > > > Ok, a sort-of-linear ramp is desired. I may then torture that into > something exponential, but opposite of how r-c time constant works. > The game is simple: Feed as much power to a small dc brushed motor as > possible without making the drive "slip". So, the faster it's turning, > the more pwm I can shove at it without increasing average current too > much. It's a toy circuit...driving a 1/24 scale electric dragster. > > Bill >How do you plan on detecting if it is slipping or not? Going to have a generator reference on the front wheels? Jamie.
Reply by ●March 15, 20122012-03-15
On Mar 16, 12:41=A0am, Bill Martin <w...@wwmartin.net> wrote:> Hi, > anyone have a favorite brand/flavor of lm358 or equivalent opamp to > recommend for a simple, low performance integrator to generate a voltage > ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to > two seconds duration, no repeating..one shot style. Looking at just > Mouser, there seem to be 23 parts in soic-8 to choose from...The Linear Technology LT1013 has rather tighter specifications. The single version - the LT1006 - is a whole lot more tightly specified and quite a bit more expensive again. You might balance the extra cost against the saving on a smaller integrating capacitor. -- Bill Sloman, Nijmegen
Reply by ●March 15, 20122012-03-15
If you want to limit torque then you want a constant current drive. Set it to just below the point of slippage then let it go. One can easily be made with an LM393 triangle generator + PWM comparator and an LM358 half as the current feedback error amplifier. The setpoint can be constant, or controlled from a second error amplifier to control speed or voltage or some other variable. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "Bill Martin" <wwm@wwmartin.net> wrote in message news:jju10m$9ef$1@dont-email.me...> On 03/15/2012 05:10 PM, mike wrote: >> On 3/15/2012 4:41 PM, Bill Martin wrote: >>> Hi, >>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to >>> recommend for a simple, low performance integrator to generate a voltage >>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to >>> two seconds duration, no repeating..one shot style. Looking at just >>> Mouser, there seem to be 23 parts in soic-8 to choose from... >>> >>> Thanks, >>> Bill Martin >> >> Since you have no requirements for linearity...or anything else... >> I'd just use a cap and a resistor. > That was version 1. >> >> The only application I can think of for a device that has "no repeating" >> is some kind of trigger for something that goes boom. > Oh, I hope not. It just shuts down due to power being turned off. :-) >> >> Precise requirements/specifications are your friend. > > Ok, a sort-of-linear ramp is desired. I may then torture that into > something exponential, but opposite of how r-c time constant works. > The game is simple: Feed as much power to a small dc brushed motor as > possible without making the drive "slip". So, the faster it's turning, the > more pwm I can shove at it without increasing average current too much. > It's a toy circuit...driving a 1/24 scale electric dragster. > > Bill >
Reply by ●March 15, 20122012-03-15
On 03/15/2012 06:59 PM, Jamie wrote:> Bill Martin wrote: > >> On 03/15/2012 05:10 PM, mike wrote: >> >>> On 3/15/2012 4:41 PM, Bill Martin wrote: >>> >>>> Hi, >>>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to >>>> recommend for a simple, low performance integrator to generate a >>>> voltage >>>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About >>>> one to >>>> two seconds duration, no repeating..one shot style. Looking at just >>>> Mouser, there seem to be 23 parts in soic-8 to choose from... >>>> >>>> Thanks, >>>> Bill Martin >>> >>> >>> Since you have no requirements for linearity...or anything else... >>> I'd just use a cap and a resistor. >> >> That was version 1. >> >>> >>> The only application I can think of for a device that has "no repeating" >>> is some kind of trigger for something that goes boom. >> >> Oh, I hope not. It just shuts down due to power being turned off. :-) >> >>> >>> Precise requirements/specifications are your friend. >> >> >> Ok, a sort-of-linear ramp is desired. I may then torture that into >> something exponential, but opposite of how r-c time constant works. >> The game is simple: Feed as much power to a small dc brushed motor as >> possible without making the drive "slip". So, the faster it's turning, >> the more pwm I can shove at it without increasing average current too >> much. It's a toy circuit...driving a 1/24 scale electric dragster. >> >> Bill >> > How do you plan on detecting if it is slipping or not? > > Going to have a generator reference on the front wheels? > > Jamie. > >It's not going to be that advanced. I would have to mount the board on the "moving parts" to really do traction control. Just doing "educated guessing", once there is enough run data to tune it up. Bill
Reply by ●March 15, 20122012-03-15
On 03/15/2012 06:33 PM, Tim Williams wrote:> If you want to limit torque then you want a constant current drive. Set > it to just below the point of slippage then let it go.This is very much the idea here. Full traction control would be nice, but not really needed to be better than what's out there now in way of motor control.> One can easily be made with an LM393 triangle generator + PWM comparator > and an LM358 half as the current feedback error amplifier. The setpoint > can be constant, or controlled from a second error amplifier to control > speed or voltage or some other variable. > > Tim >Version 1 does pretty well with just an r-c curve to control the pwm ramping up, but it's really not the right shape for the ramp. Backwards, actually! pwm is done by a nifty little chip from Supertex, meant to be controlling cooling fans in electrical racks. Darn thing comes Soooo close, but doesn't quite do everything needed. Bill
