Square-waves from a chip other than NE555, please?

[Al (astral highway)]

Wonderfully interesting and helpful contributions , thank you all! One things is the 'chicken and egg' nature of the application - I know the approx required operating frequency to within 150KHz but I won't know exactly until empirically , when I run the big oscillator attached to the PLL!

[dragonser]

Hi,
I think the Vellerman kit uses a 555, but doesn't have a decoupling cap on pin 5 ?
I found that the frequency drifted with the changes in the battery supply voltage which wasn't good for the application I wanted it for.
regards Peter B

[Al (astral highway)]

Originally Posted by dragonser

I found that the frequency drifted with the changes in the battery supply voltage which wasn't good for the application I wanted it for.

Sure it will! The control voltage inside the chip is around 1/3 of the volts on the power supply, so this is an inherent property of the chip. It is fine with a stabilised power supply ...not to go too far OT

[mhennessy]

It depends on how it's wired up. Using the standard astable circuit, it's reasonably good - less than a percent per volt of supply voltage change IIRC. The two thresholds are linked to the supply (1/3 and 2/3), but the charging currents are proportional to the supply. The equations that determine each of the time periods do not have the supply voltage in them.

[mhennessy]

Originally Posted by merlinmaxwell

SMT is nothing to be scared of...

Personally, I agree

And the various adaptor boards which can be found cheaply are really good for those who prefer conventional construction. SOT23 is not too small to deal with, given strong light and perhaps some magnification if needed.

Today, a lot of the interesting new products are SMT-only. Many big manufacturers have stopped making the TO92 package, which is a sign of things to come.

[MrBungle]

The only problem with surface mount is prototyping and low power handling capacity. I still haven't worked out a good solution to the first problem. The second problem occasionally throws a component at my eye on power up. The little 0802 LEDs go off like flame throwers.

Back on topic, take a look at: http://www.americanradiohistory.com/...PW-1974-01.pdf pp853 on astable circuits. Amazing how far you can take a few transistors.

[Maarten]

Why not use the CMOS 4060? It has both an oscillator and a ripple counter thzt cn be used as a divider.

[MrBungle]

That's a really good idea. I've used a couple of them in clocks in the past. 32.768KHz watch crystal gives 2Hz out as well which is really handy.

[qazxsw123]

Use a CD4060, it has a CR cct and divider to allow a range of values and times. Often used as a long delay timer.

[JayBee66]

Do you have an Android tablet or smartphone?

I use an app to provide signals to put through devices.

https://play.google.com/store/apps/d...enerator&hl=en

This one has all the bells and whistles. Dual channel. Phasing. Modulation. Square. Sine. Triangle. Noise. The works.

I needed to cut down on gadgets. I was tempted to get a function generator or build a circuit but now there is no need. Time saved for fixing things.

[Al (astral highway)]

Update : I nearly went for David G4EBT's solution - thank you, David , a handy little CMOS chop you're recommending in this package, definitely one to come back to ,and I appreciate the effort that went into your post . The applet is very useful , too.

In the end , I'm going instead for a dedicated PLL, the CD4046. This has a VCO good to the 1.3Mhz I need, as well as some other features that make it attractive in this application .

I've learned a lot about the various choices on this thread , and I will make time to study some of the device me mentioned and try them out .


JayBee66, yes. There are some nice little apps out there and I have one called Signal Gen. These are indeed useful for for audio frequencies, and I will be modulating the cathode (filament centre tap ) of my big triode-connected pentode via the output of this, through isolation circuitry . The frequency I need for this is very low, so the app is ideal. The original post was more directed at RF-capable ideas. Thank you though.

[Al (astral highway)]

Originally Posted by David G4EBT

...It also goes under the name of 40106 and 40014

Ah, but is not to be confused with the Phillips HEF40106BP? (which is what turned up when I ordered using '40106' from EBay). The HEF40106 device operates at approx 1/2 of the expected design frequency using the applet you kindly resource here..


So with 47pF pin 1 to ground and R 12K, I'm getting a nice clean square wave but approx 750KHz.

[Oldcodger]

Come late to this one, otherwise I'd ask if anyone has a copy of Electronics circuit design Winter 1980 ( Part 1/2 -I don't know to pass on to the OP) ,but it's got a brilliant section on both CMOS Astable and Monostable circuits, most using either 4001/4011, and a few other components. Monostable timings are given, but few details on the frequencies outputed, but that could be derived on breadboard.
Couple of circuits that might interest the OP. Both uses either 4001 or 4011 ,a resistor or two and a capacitor. cAN POST UP THE CIRCITS IF INTERESTED.

[Al (astral highway)]

Originally Posted by Oldcodger

... anyone has a copy of Electronics circuit design Winter 1980 ...
Couple of circuits that might interest the OP...

Hey, what a great memory! Yes, I'm familiar with the 4001 with its four gates and know it's still around.

Just to keep this on track, I'm interested in devices, rather than circuits, thank you, so please don't worry about posting the article from PW.

Also, I'm only those that are RF capable and rock solid at greater than 1MHz.

Atm, I'm most interested in any comment on post number 32...

Thank you

[MrBungle]

Just out of interest, have you considered the VCO block in the 74HC4046?

If you're building a PLL, that's pretty much a canned device. It's same functionally as the 4046 but a hell of a lot more stable and will kick out a few MHz quite easily.

Also the MC145151P, still available from Spectrum Communications is pretty nifty.

And then there's the DDS route. Cheap AD9850 boards will deliver a nice square wave that is frequency locked.

[Al (astral highway)]

Originally Posted by MrBungle

Just out of interest, have you considered the VCO block in the 74HC4046?

If you're building a PLL, that's pretty much a canned device. It's same functionally as the 4046 but a hell of a lot more stable and will kick out a few MHz quite easily.

Hello! Thank you .... Just to clear up any confusion, yes, the 74HC4046 is the chosen candidate for my PLL.

En route, I'm investigating some other chips as RC controlled oscillators, just for my own enlightenment.

The note I made yesterday on the 40106 was because before I work out the PLL's RC values, I'm separately constructing a high powered oscillator with a big RF output to test the exact operating frequency of two very large inductors that are close coupled - so physically large that they will swamp the feeble output of low-powered signal sources. This is just a deviation from the main goal, but a necessary one. Hope that clarifies things!

[MrBungle]

I see! A collection of other square wave sources for consideration off the top of my head:

1. 566 VCO - nearly unobtainable for a reasonable amount of money.

2. Ignoring the topic title a bit, but the 555. The CMOS 7555 version from Intersil isn't too bad. Standard bipolar ones are horrid. To correct the somewhat wonky duty cycle, run it at 2x the desired frequency and then through a 74hc74 as a /2 divider. Good to 2.5-3MHz.

3. 74hc14 - pretty stable due to low bias current. Nice xtal, RC and with some playing around, LC oscillator. 40106 is usable but not as fast and they blow up if you look at them wrong.

4. 74hc4060 and 74hc390 chain - I've got one of them on the bench now dividing an 8MHz crystal down to 500, 50, 5 and 0.5 Hz for a frequency counter timebase with stable duty cycle and good rise times. The HC4060 will run from an RC oscillator absolutely fine.

5. MAX038 - good to 20MHz. Technically a function generator but will kick out a nice square wave.

6. XR2206 - good to about 1-2MHz. Also a function generator.

9. LM311 or equivalent comparator can be configured to kick out a square wave. In the on state, the capacitor charges via the feedback resistor. In the off state, the capacitor discharges via the feedback resistor. A good low bias current one is quite frequency stable.

I'll probably think of more later.

Really though, if you want RF that means frequency stability which means LC or Crystal based circuits. From the above, they can be derived. I'd probably go for a tuned LC colpitts and drive a few big class C stages with it then stick a low pass on the output if you want big RF power. If you can put up with a few tens of Hz drift that's probably easiest.

[Ed_Dinning]

Hi Al, following on from Mr Bungle, look up comparators, a version of the op-amp but normally with an open collector output.
A vast number of devices to choose from, some of which will operate up to 100MHz.

Ed

[MrBungle]

Make sure you have some hysteresis though as the fast ones go nuts otherwise with the tiniest bit of noise:

[img]http://i.**********/0KcXo3P.jpg[/img]

[David G4EBT]

Out of curiosity I've just spragged together a resistor and capacitor to a 74HC14 per the circuit I posted at post #10 above.

As I said then, a square wave generator doesn't get any simpler than an IC a resistor and a cap. I didn't make any attempt to shorten the wiring, just a 50pF cap that happened to be to hand, and a 22k resistor, the frequency coming out at 1.352MHz. Not a perfect square wave, as can be seen from the rise time and mark-space ratio, but clean, and not bad considering it's just tacked together. (about 4V p-p).

I'm a simple soul so simple solutions are what I go for - complicated stuff is beyond my wit and above my pay grade - small things amuse small minds!