Design Challenge

[dbanner]

Micro is probably the best way for doing this task. Why prohibit it's use?
There exists a patent which has a circuit using a differentiator to do this sort of magic. Can't remember the title of it.

[Teleno]

If you could at least post a timed waveform of the input and the desired output it would help.

[Skippy]

A few more specifics may help us.
Does the signal always start off from zero volts before rising? Is the dv/dt critical, ie. if it rises at 10 mV/us or 50 mV/us , you don't want it flagging a Logic Hi ?
Is there any other 'false positive' condition we should know about?

If you generated a signal that FELL at 15 mV/us , and added it to your waveform, you would end up with a flat-ish output, which might be easier to distinguish from the unwanted signals?

[Sean_Goddard]

Therein lies the problem. The slope and thus discrimination is, sadly, VERY coil dependent and it is VERY time consuming to wind and trim coils of different sizes (one is a 10mm diameter coil for ferreting out nuggets in rivers) as the machine is a 6KHz fast PI designed specifically for very small gold. The idea is to work the spoil heaps of a local mine on which I have been given free reign to keep WHATEVER I find, but working the surrounding areas requires a license and the cost is just stupid. The best part is I have access to a rock crusher to turn the rocks into gravel. I don't expect to get rich, but it will be fun and pay for the beers.

The mine is due to reopen, but the old extraction methods were not very efficient thus there are (from what I could see by eyes only) a LOT of VERY small nuggets (pin head sized) and flakes in the spoil heaps and it's all MINE (pardon the pun).

[Qiaozhi]

Have a look at the envelope follower circuit of the "Off-Resonance" probe in ITMD.
The circuit produces a logic one at the output of the comparator while the input signal is rising, and a logic zero shortly after it levels off.
You'll just need to adjust the time constants to suit your particular needs.

[Sean_Goddard]

I am struggling to get a circuit to work despite all the calculations showing it SHOULD, so....Here is your mission;

I have a signal with an dv/dt of 15mV/us for 56us then the signal levels off at 710mV final value.

What I am trying generate a logic "1" for the rise period, but as soon as the signal levels off, I want a logic "0". Now I know a differentiator & schmitt trigger should do the trick, but I simply cannot get the circuit to work.

I have spotted something in the Rx waveform of a PI which gives some VERY consistent results and using some magic circuitry processing, I get this sloping output. By processing the slope in the manner above, I want to gate another signal which will provide REAL discrimination (yup Dave Emery isn't the only one who has cracked this at last). The only thing is that I can't post any schematics of the PREVIOUS part of the circuit which generates the slope, and I do not intend to patent this idea as there will be only TWO units made (one for me and one for a friend).

The theory all works out according to the simulations and calculations and I have but this one stumbling block so any ideas people? NO, why don't you try it a different way is NOT the solution, this is the ONLY way (unless I use a micro which I don't want to do for noise reasons).