Ideas?

Archiver

Hello,

I'm working with a sensor whose output swings from 9 vdc to 2 vdc when
activated.

I would like to detect this transistion with a stamp pin. (1.4 vdc threshold)

I can not load this signal down. My best thought at the moment would be to
use an Inverting schmidt trigger, like a mc40106. this should convert my
signal into a 0 to 9vdc signal, then i could use a resistor divider to chop
it in half.

any ideas? suggestions?

thanks

Steve

Archiver

>Hello,
>
>I'm working with a sensor whose output swings from 9 vdc to 2 vdc when
>activated.
>
>I would like to detect this transistion with a stamp pin. (1.4 vdc threshold)
>
>I can not load this signal down. My best thought at the moment would be to
>use an Inverting schmidt trigger, like a mc40106. this should convert my
>signal into a 0 to 9vdc signal, then i could use a resistor divider to chop
>it in half.


The CD4049 and CD4050 are also level changer chips.

Would 10 or 20 megaohms be too much loading? If not, it's easy.

Happy holdays,
-- Tracy

Archiver

Thanks Tracy,

Seasons greetings,

I will keep those parts in mind.

Larry G suggested I use an op-amp as a unity gain follower to provide the
buffering, then I attached a 10 k pot to the output and used it to fine
tune the division, centered around the 1.4 vdc threshold of the stamp pin.
It works great, and I happened to have an lm741 amp laying around.

Now i have another concern. I'm using my stamp to detect a transistion of
this signal from high to low, and when this happens I'm using another stamp
pin to drive a 2n2222 which then drives a DPDT throw relay(with a
supression diode). The relay is switching the polarity of a electronic ball
valve, which opens and closes the valve. The ball valve is fused for three
amps and draws close to this during transistion.

I'm powering the stamp and valve from a 12 vdc gel-cell (18 amp/hr).

When i observe the 12 vdc input to the stamp with a scope, there is a large
voltage spike when the valve is energized, for a few microseconds. This
does not reset the stamp, though
this can't be good?

Adding semi-large capacitors(1,000mf) close to the stamp seem to help only
slightly.

I've also tried running the stamp and valve from different supplies with
the ground tied together, and this doesn't seem to help either?

It sounds like this may be a good time for me to learn how to isolate the
two systems with seperate power supplies and use an optocoupler for
activation?

tia,

Steve