555 Calculator

What about a resistor from output to the cap? You may want to use a CMOS

Saves a resistor in any case.

Thomas

put a 100 ohm resitor in series with the hot side of the pot. othewise with it wound all the way down it'll be trying to discharge the powersupply.

Crap repeatability.

Thanks for knocking yourself out on that :) I used Jason Betts suggestion; subbed R1 with a 100 ohm trimmer and used a 22NF. Works good; apx 46K on the trimmer gives 1ms width and pertneer

What is your Vcc and what is your load? The half-way point coincides with Vcc/2 across the timing capacitor where the THRESH comparator is just entering complete cutoff and the TRIG comparator is on the edge of linear for low Vcc. If Vcc is small enough, this may reduce the pulldown drive ever so slightly to cause a higher Vce,sat on the output.

--- It may work for you, but it's not "poifect" if you're looking for a

-- John Fields Professional Circuit Designer

doesn't 50% duty cycle imply that the output be on the same time frame as it is off ? i don't see where the rail-to-rail comes into this? since the trigger and threshold are at 33% and 66% of Vcc i don't see where the in ability to effect 50% duty is coming from ?

Fsck you are a priceless piece. I used the CIRCUIT once.

If the 1kHz is *critical*, what is the tolerance? If it is within +/-5% I wouldn't even be considering a 555.

Well, a lot of capstan motor servos on Studer pro audio tape decks used 555s for decades. They worked extermely well. I suppose the designer just new how to use them properly

martin

Without knowing the configuration it's a bit diffcult to comment. For all I know there is tachofeedback, in which event the repeatability factor is largely removed.

I=V/R if the output gets closer to the rail one way than it does the other

diifferent charge/discharge currents will result.

What youse guys failed to note in your circuit recommendations is that output freq varies with VCC. Since this application is a 12V marine elect. sys, variation in system voltage causes changes in motor RPM. Perhaps useful for something, but not for me. Modified the circuit with a 8V reg, since a 5V reg drops the output below TTL and the stepper board doesn't like it. BTW: this driver runs a stepper to rotate a radar antenna. Thus the RPM req. Variation in antenna RPM causes the display to lose sync. Back on track now.

JR North wrote:

I must admit I havent look at the typical Studer circuit in long long. But I was always astounded how good this little chip worked in the servo

martin