micro power square wave oscillator

An MSP430 micro might be able to do that, worth checking. Not 5V though.

Dave.

I'd investigate the oscillator in the 4046. Beautiful symmetry, and it's pretty low-power too. Hope you're not trying to drive much of a load though.

... etc.

Chris

A simple two transistor astable multivibrator should do the job. You'd need low capacitance transistors - the SD214 is one part that might just do the job

The BFR92 5GHz broad-band transistor would walk it, since it is an appreciably lower capacitance part

but you'd need to put some 22R of low inductance (surface mount) resistor in series with each base to stop them oscillating at a GHz or so on the stray inductances and capacitances around your layout. A ferrite chip (non-wound) inductor might do the same job - they weren't widely available back when I was playing with the BFR92 and it's PNP complement.

Note the base of the BFR92 can't take more than 2V of reverse voltage

- on a 5V supply you have to be careful that your circuit doesn't destroy the transistor when it turns it off. You should really build and test the circuit in LTSpice before you risk blowing up real parts (not that they are all that expensive - a dollar or so each).

-- Bill Sloman, Nijmegen

I am thinking about a PUJT as a relaxation oscillator, perhaps coupled to a CD4060, maybe? Have you considered that approach?

Jon

I was thinking of loading too.. Mmmmm....

1/100Khz = 10uS

Let's say a risetime and falltime of 1uS. Say supply = 5V

By I = C dv/dt And assuming a 100% efficient circuit..

10uA = C 5V/1uS

C = 2pF !!

With those assumptions and if I did the math right, it suggests you can't even drive a typical scope probe without going over the supply current spec.

D from BC British Columbia Canada

100kHz crystal oscillator or a 200kHz ceramic resonator oscillator followed by a FF if you need very close to 50% duty cycle.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I suppose you are right. Dispels the PUJT relaxation thingy, I think, as it dumps the charge each cycle and I think the 2n6028 has 100's of pF, roughly. Not good.

Trapezoidal rise/fall, then? ;) Or perhaps draw some charge at first and then just move it back and forth in an LC + xtl tank with high Q, replacing losses?

How do the watch folks do it? There must be some serious remodeling of crystals for simulation work there (vastly more complex understanding of them) in order to design something as efficient as I've seen from them. Anyone know the details here?

Jon

Its hard to beat the LTC1540 for low current. You will need really high resistor values so don't breath on the PCB.

You'd need low capacitance transistors, so the BFR92 and its PNP complement, the BFT92 might be useful

Like the BFR92, the BFT92 will need a 22R (or bigger) base stopper, and can't take more than 2V of reverse bias across the base-emitter junction.

-- Bill Sloman, Nijmegen

--
Can you post a schematic showing something that works, or do you just
want to pretend to, as usual, know what you\'re talking about?

JF

"D from BC"

** Nonsense.

The load charging current only flows during the rise-time of the square ave - which even in your hand-picked example is only some 10% of the time.

The average supply current is therefore ( for your example) only 1 uA.

Similar math applies for faster rise times making the AVERAGE current draw essentially independent of the rise-time for fixed frequency and load C.

..... Phil

You just reminded me of the HA7210, which just needs a crystal and a cap to make a (mostly) square wave oscillator. The data sheet suggests supply currents around 21uA @ 5V to 38uA @ 8V. Not 10uA, though.

I see that the LTC1540 has low requirements when it just sits there doing nothing, but would it do better than the HA7210 once you surround it with four resistors and a cap, or so.

Jon

... for 100kHz.

Jon

a

an

Since I'm posting via a telephone modem - my brother's house in Sydney has every luxury except ADSL - posting a schematic would be time- consuming. An LTSpice text file would work, but who needs it?

The patent I pointed to does include a number of schematics, and if you need a schematic for conventional two-transistor astable multivibrator, you can find one with google.

You don't seem to appreciate precisely how simple a two-transistor astable actually is. I did once see someone build a two-transistor multivibrator that blew up its base-emitter junctions, whence the warning, but it isn't a complicated circuit.

-- Bill Sloman, Nijmegen

Posting binaries in this newsgroup would be not a good idea. But why is it time consuming? Lets assume a 56k modem. A JPEG image of about 200kB needs less than a minute to upload, for which you can use one of the free image hosting services and then posting a link to it.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

Yes, average current is just C*V*f

Posting binaries to ths news-group is not an option - when I'm at home I could post to abse, but I can't here.

I'd have to stick it on my web-site as a new page - which takes quite a lot of fiddling around - if I thought that it was worth the effort. Since astable multivibrators are almost trivially simple, I'd prefer not to further clutter up my web-site for benefit of the terminally dim.

-- Bill Sloman, Nijmegen

--
The OP?

Not that I'm interested in an astable multivibrator schematic, but uploading images is as easy as clicking on the upload button, e.g. with this image service:

A breakout board for a display connector I designed and soldered some weeks ago:

I routed this by hand. It was interesting to see how the Eagle autorouter result looked like, with two sides and multiple vias :-)

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de