555 timer

Is it also not true that it must be pulled high (or allowed to go high) at the end of the reset interval, before the timing cycle will start?

Thanks, Rich

A good solution is :

Fero

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The drive current is a bit higher for the bipolar version, some of the CMOS types won't handle as much supply voltage.

AFAIR, everything else is better on the CMOS- 100kHZ is getting to the limit for the bipolar type, but some of the CMOS ones will do MHz. With CMOS, swing is to the rails, no big spikes of current, no bias current to speak of.

Best regards, Spehro Pefhany

Seconded. I don't use bipolars anymore at all. ...Jim Thompson

Thanks, George H. vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

The bipolar 555/556 gives up the ghost at around 200kHz, years ago I kit built a TV pattern generator with 555 sync generators - the 15.625kHz line timebase 555 proved impossible to calibrate, it was pretty flaky and wouldn't stay set.

The bipolar 555 won't be any good as a stable frequency generator at 100kHz, the CMOS version is claimed to be good upto about 2MHz but has rather limited O/P drive capability.

Back in college the final project in a course was to build something. I made this bike speedometer/odometer (magent on wheel and reed realy.) I used a 555 for timing and the tempco of the carbon comp resistors I used killed the stability. But I only learn by making mistakes..... In this case I don't care if the frequency drifts around a bit.

George H.

Hz,

Years ago I too did a project using a 555 and it would drift a bit depending on what you're doing.. So, I had some ovens laying around that worked perfectly :).

P.S. choice of R's and Caps also makes a difference.. You can also bond a diode on the case of the chip to be used to help counter act thermo issues.

Jamie