How inaccurate is a 555 or 7555 REALLY?

I suggest that you do some measuring...

Oops, I forgot the extra divider gates needed. Perhaps the 74HCT40104 as someone else mentioned might be better... Either way you need a 10.752MHz oscillator and some form of 15 stage divider.

Space-wise I still think a small 8pin microcontroller is a better solution. Do you need 50-50 duty cycle?, if so you'll need an extra D flip-flop on on the output.

Dave :)

Didn't help. There wasn't all that much headroom t play with, and a smaller collector-base bias meant that the Early effect was more signiificant to start with - anything we won on the swings we lost on the roundabouts.

My boss might have been over-optimistic, but he'd been trained at the Royal Radar Establishment, working for Peter Baxandall, and his electronics was very good indeed - I learned a great deal from him.

I suggest you get you head out of your ass. I've been designing IC's since the beginning of time... ratiometric is what it's all about.

...Jim Thompson

On 3 Dec 2006 20:01:11 -0800, "WildIrish" wrote:

If you switch to 3V you can use common 74HC or 4000 family logic and use whatever package size you need to fit into your box.

I've attached an LTSPICE circuit list using what amounts to a 4024

That's an error of about 0.025%

I would've used a 4060 counter, which includes the oscillator but, unfortunately, this type of counter must be reset to zero once the proper number of counts has been reached and, In a 4060, the oscillator is stopped when the chip is reset.

The output of the circuit will be a 50% duty cycle 420.103Hz square wave.

Version 4 SHEET 1 2244 800 WIRE 1280 -1008 992 -1008 WIRE 1552 -1008 1280 -1008 WIRE 1680 -976 1440 -976 WIRE 1280 -912 1280 -1008 WIRE 1552 -912 1552 -1008 WIRE -576 -864 -880 -864 WIRE -96 -864 -496 -864 WIRE 192 -864 -96 -864 WIRE 1056 -864 192 -864 WIRE 1200 -864 1056 -864 WIRE 1408 -864 1360 -864 WIRE 1440 -864 1440 -976 WIRE 1472 -864 1440 -864 WIRE 1728 -864 1632 -864 WIRE -96 -832 -96 -864 WIRE 192 -832 192 -864 WIRE 1056 -832 1056 -864 WIRE 1728 -832 1728 -864 WIRE 1200 -816 1152 -816 WIRE 1408 -816 1408 -864 WIRE 1472 -816 1408 -816 WIRE 1680 -816 1680 -976 WIRE 1680 -816 1648 -816 WIRE 1152 -736 1152 -816 WIRE 1152 -736 -768 -736 WIRE 1728 -720 1728 -752 WIRE -496 -704 -688 -704 WIRE -208 -704 -496 -704 WIRE 80 -704 -208 -704 WIRE 368 -704 80 -704 WIRE 656 -704 368 -704 WIRE 944 -704 656 -704 WIRE 992 -704 992 -1008 WIRE 992 -704 944 -704 WIRE 1232 -704 992 -704 WIRE 1280 -704 1280 -768 WIRE 1280 -704 1232 -704 WIRE 1552 -704 1552 -768 WIRE 1552 -704 1280 -704 WIRE -368 -656 -624 -656 WIRE -80 -656 -336 -656 WIRE 208 -656 -48 -656 WIRE 496 -656 240 -656 WIRE 784 -656 528 -656 WIRE 1072 -656 816 -656 WIRE 1360 -656 1104 -656 WIRE -496 -608 -496 -704 WIRE -208 -608 -208 -704 WIRE 80 -608 80 -704 WIRE 368 -608 368 -704 WIRE 656 -608 656 -704 WIRE 944 -608 944 -704 WIRE 1232 -608 1232 -704 WIRE -624 -560 -624 -656 WIRE -576 -560 -624 -560 WIRE -336 -560 -336 -656 WIRE -288 -560 -336 -560 WIRE -96 -560 -96 -768 WIRE -96 -560 -128 -560 WIRE -48 -560 -48 -656 WIRE 0 -560 -48 -560 WIRE 192 -560 192 -768 WIRE 192 -560 160 -560 WIRE 240 -560 240 -656 WIRE 288 -560 240 -560 WIRE 528 -560 528 -656 WIRE 576 -560 528 -560 WIRE 816 -560 816 -656 WIRE 864 -560 816 -560 WIRE 1056 -560 1056 -768 WIRE 1056 -560 1024 -560 WIRE 1104 -560 1104 -656 WIRE 1152 -560 1104 -560 WIRE -768 -512 -768 -736 WIRE -656 -512 -768 -512 WIRE -576 -512 -592 -512 WIRE -368 -512 -368 -656 WIRE -368 -512 -400 -512 WIRE -288 -512 -368 -512 WIRE -80 -512 -80 -656 WIRE -80 -512 -112 -512 WIRE 0 -512 -80 -512 WIRE 208 -512 208 -656 WIRE 208 -512 176 -512 WIRE 288 -512 208 -512 WIRE 496 -512 496 -656 WIRE 496 -512 464 -512 WIRE 576 -512 496 -512 WIRE 784 -512 784 -656 WIRE 784 -512 752 -512 WIRE 864 -512 784 -512 WIRE 1072 -512 1072 -656 WIRE 1072 -512 1040 -512 WIRE 1152 -512 1072 -512 WIRE 1360 -512 1360 -656 WIRE 1360 -512 1328 -512 WIRE -880 -464 -880 -864 WIRE -768 -464 -768 -512 WIRE -880 -352 -880 -384 WIRE -768 -352 -768 -384 WIRE -768 -352 -880 -352 WIRE -688 -352 -688 -704 WIRE -688 -352 -768 -352 WIRE -496 -352 -496 -464 WIRE -208 -352 -208 -464 WIRE -208 -352 -496 -352 WIRE 80 -352 80 -464 WIRE 80 -352 -208 -352 WIRE 368 -352 368 -464 WIRE 368 -352 80 -352 WIRE 656 -352 656 -464 WIRE 656 -352 368 -352 WIRE 944 -352 944 -464 WIRE 944 -352 656 -352 WIRE 1232 -352 1232 -464 WIRE 1232 -352 944 -352 WIRE 1408 -352 1408 -816 WIRE 1408 -352 1232 -352 WIRE -880 -320 -880 -352 FLAG -880 -320 0 FLAG 1728 -720 0 SYMBOL Digital\\\\dflop -496 -608 R0 SYMATTR InstName A2 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop -208 -608 R0 SYMATTR InstName A3 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop 80 -608 R0 SYMATTR InstName A4 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop 368 -608 R0 SYMATTR InstName A5 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop 656 -608 R0 SYMATTR InstName A6 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop 944 -608 R0 SYMATTR InstName A7 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop 1232 -608 R0 SYMATTR InstName A8 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL voltage -768 -480 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 0 1e-6 1e-6 1.525879e-5 3.051758e-5) SYMATTR InstName V1 SYMBOL Digital\\\\inv -656 -576 R0 SYMATTR InstName A1 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL voltage -880 -480 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 .001 1e-6) SYMATTR InstName V2 SYMBOL diode 1040 -832 R0 SYMATTR InstName D4 SYMATTR Value 1N914 SYMBOL res -480 -880 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL Digital\\\\dflop 1280 -912 R0 SYMATTR InstName A9 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\dflop 1552 -912 R0 SYMATTR InstName A10 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL res 1712 -848 R0 SYMATTR InstName R3 SYMATTR Value 100k SYMBOL diode -112 -832 R0 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 176 -832 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 TEXT -848 -328 Left 0 !.tran .01

"John Fields"

This site has some of the history of the tuning fork watch crystal.

....... Phil

--- Nice, thanks. :-)

I still have a few of their early crystals, sealed in glass and, for that time, pretty far out, being surface mount.

Speaking of early surface mount stuff, have you ever heard of a device called a "Gifft Recorder"?

It was a SONAR transmitter/receiver invented by a man named Tom Gifft which output about 1200 watts into a UQN transducer (if I remember correctly) and used surface mount TI chips on all of its PCBs.

Back when I was a young lad and worked for an outfit named "Marine Acoustical Services" in Miami, Florida, I regularly went to sea as the ship's radio officer and did double duty running the Gifft Recorder.

One of its claims to fame was a stainless steel belt that had three tabs welded to it, 120 degrees apart, which traversed a wet paper belt which would change color when an echo was detected.

Also on the belt was a series of punched-out holes with an optical emitter shining through the holes on one side and a detector on the other working against a crystal time base. An early PLL.

Oh well, just reminiscing...

-- JF

Of course, if you could find an example where I was unreasonably easily provoked, or "accidentally" produced a grievous insult, you'd quote it, thus converting a pointless troll into something worth reading.

If you say so John - since you don't know my wife or her colleagues, you are free to let your imagination run wild. Pity you haven't got an imagination that can usefully exploit this lack of factual restraint, let alone any more modern electronic component than the 555.

..do it in software..

Do tell; that is ASS-u-ME-ing that the ratios are *constant*.

Who do you think you are, Eeyore or some similarly IGNORANT person?

Please explain on me how the ratios are not. (Assuming you have even the vaguest clue about resistor TYPES.)

...Jim Thompson

Sounds like you may need an education in electronics...

Sounds like you need a PLONK ;-)

...Jim Thompson

I wonder how many of your IC's Robert has used and didn't even know it? ;-)

Dave :)

Your search skills aren't exactly impressive, but the intelligent reader will still conclude that there are many fewer than thousands of examples out there, with the likeliest number being zero. Since I seem only to have cranked out 6520 postings over the past ten years, there is an upper limit to the examples that you could find.

They are (mostly) nice people, but probably even better-informed in their subjects than I am in mine - not the sort of company that you seem to keep, let alone know anything about.

You've got me there. I'm just flat hunting. On the other hand the MC68HC908 is the 2002 version of Motorola's 8-bit microcontroller, going back back via the 6805 to the original 6800 from 1975. RISC and DSP seem to have passed you by.

It isn't a "bad" chip, but very rarely an acceptable candidate for any job in serious electronics these days. There was a thread about this here a while back, and the concensus was that most professional electronic engineers don't seem to be using it any more.

But he has me all concerned. Maybe they're not really working ?:-)

...Jim Thompson