# How to set automatically unknow trigger levels?

Discussion in 'Electronic Design' started by [email protected], May 10, 2007.

1. ### Guest

Does somebody know how can I solve this problem?
I need to find out electronically the highest and the lowest voltage
in order to set automatically
two trigger levels of a unknown signal with range +10 and -10V,

For instance, once the unknown signal amplitude reaches 8V as the
maximum value and 2V as the minimum, hence
I need to set the trigger levels of a comparator for activating other
devices with relays at the max and min. But the next
time it will reach 7V and 1V respectively.

Because the input signal and the trigger thresholds are not constant,
I do not know how I can solve this in the cheapest way as possible.

Any advice is appreciated.
Nick

2. ### Anthony FremontGuest

What do you mean with "the next time", how much delay between itterations?
How fast does the signal change?
It would seem that two DACs controlled by a micro could the set the input
levels for the comparators depending upon how fast this all has to work.

3. ### Robert LatestGuest

Why use a mainframe computer when an analog integrator will work?

robert

4. ### Rene TschaggelarGuest

Sure, and by what signal ist the integrator
controlled ? Meaning what is the input of
the integrator ? There might be multiple
trigger density maxima between the voltage
boundaries.

Rene

5. ### Anthony FremontGuest

Mainframe? The OP didn't even describe an algorithm explaining how the
levels would be chosen, how do you know that an integrator will suffice?

6. ### MooseFETGuest

Basically what you want looks a little like this:

U1
IN-------!+\ D1 U2
! >----->!----+-----!+\
---!-/ ! ! >---+--OUT
! C1 === --!-/ !
! ! ! !
! GND --------+
! !
-------------------------------

If the input goes above the output, the output of U1 swings positive
and charges up C1 to bring it to a matching voltage. When the input
starts to fall, U1 swings back down, the diode back biases and the
output remains at the positive value.

Now all you need is a voltage divider and comparitor to make the
signal you want.

This design has some serious problems, however. There is no path for
C1 to ever discharge. If the frequency is more than a few KHz, U1's
job is near imposible. D1 has to be a very good diode. U2 has to
have low bias current but be fast.

Each of these can be solved in specific cases so if we know more about
the frequencies etc, we may be able to go further or perhaps just this
little push start will have you see how to solve it.

7. ### D from BCGuest

Perhaps...check out the min-max detector,
Patent 4315220
4 diodes, 1 op amp and a capacitor
See google patents for sheets.
D from BC

9. ### Stanislaw FlattoGuest

Automatic setting of unknown values is best done in programming using
random number generator(s) and praying.
Note: can drive anyone loco, including working hardware.
BTW this is "design" gathering, try to fit.

Have fun

Stanislaw.

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