Hello all,

I have a question for the group...I have built inverting and non-inverting
Schmitt Trigger with symmetrical and asymmetrical trigger points using an
LM741 op-amp with no problems. I would like to make these same circuits
using a single supply op-amp, like the LM324. Is this possible? If so, can I
make it asymmetrical so that the lower trigger point is above 0V?

Thanks in advance.

On Aug 9, 4:07 am, "Zucker" <zuck...@comcast.net> wrote:
> Hello all,
>
> I have a question for the group...I have built inverting and non-inverting
> Schmitt Trigger with symmetrical and asymmetrical trigger points using an
> LM741 op-amp with no problems. I would like to make these same circuits
> using a single supply op-amp, like the LM324. Is this possible? If so, can I
> make it asymmetrical so that the lower trigger point is above 0V?
>
> Thanks in advance.

Hi, Zucker. If you've got a single supply, and you want digital
output anyway, why not just use a comparator?

The LM393 is a dual single supply comparator that will do the job.
Look at the "Inverting Comparator with Hysteresis" application circuit
at the bottom of p. 9 of the data sheet for your answer.

http://cache.national.com/ds/LM/LM193.pdf

The three 1 meg resistors in the circuit allow the switching points at
1/3Vcc and 2/3Vcc. Change the resistors to change the switching
points.

Good luck
Chris

Zucker wrote:
> Hello all,
>
> I have a question for the group...I have built inverting and non-inverting
> Schmitt Trigger with symmetrical and asymmetrical trigger points using an
> LM741 op-amp with no problems. I would like to make these same circuits
> using a single supply op-amp, like the LM324.

Just replace the 741 with the LM324, and the circuits should
work quite similarly, except that the output will swing
closer to the negative supply voltage and this will increase
the hysteresis, slightly (lower the more negative
threshold). There is nothing preventing you from using a
324 in a dual supply circuit.

> Is this possible? If so, can I
> make it asymmetrical so that the lower trigger point is above 0V?

On Thu, 09 Aug 2007 11:55:33 -0400, John Popelish wrote:
> Zucker wrote:
>> Hello all,
>>
>> I have a question for the group...I have built inverting and non-inverting
>> Schmitt Trigger with symmetrical and asymmetrical trigger points using an
>> LM741 op-amp with no problems. I would like to make these same circuits
>> using a single supply op-amp, like the LM324.
>
> Just replace the 741 with the LM324, and the circuits should
> work quite similarly, except that the output will swing
> closer to the negative supply voltage and this will increase
> the hysteresis, slightly (lower the more negative
> threshold). There is nothing preventing you from using a
> 324 in a dual supply circuit.
>

Yes, there is! An LM324 won't fit into an LM741 socket!

(IOW, OP will have to rearrangs a few connections. )

Cheers!
Rich