Help with opamps

[ullisees]

@jim-p On my schematic I have put in Lm393. Still not working correctly so am looking at what I'm doing wrong

[anon27210439]

Post your last version and we take a look.

[ullisees]

comparator circuit LM393.PDF (9.8 KB)
I have got this circuit to turn the LED on and off as I want it to.

How would I get it to work with 2 comparators for 2 inputs

[rsmls]

Uploading your schematic as an image is a lot more convenient than PDF.

@ullisees

How would I get it to work with 2 comparators for 2 inputs

Replicate the same circuit with appropriately chosen resistors.

I'm surprised that you end up needing 10Meg for R10. Sounds kind of high; I'd scale down everything by an order of magnitude or so (except R7).

[ullisees]

@rsmls

I'm surprised that you end up needing 10Meg for R10.

That was the only value that would work. Anything lower and it didn't work

[DaveX]

@ullisees

How would I get it to work with 2 comparators for 2 inputs

The circuit in #9 (and #10) makes an adjustable deadband gap by essentially connecting one end of a pot to your R5(1) node, the other end to ground (or a node partially towards ground), and the wiper of the new pot to the second comparator reference. This makes a reference voltage lower than the one created by R5&R9.

[ullisees]

comparator circuit LM393.PDF (10.7 KB)

Does this look correct. It is working as I want on the simulator

[jim-p]

You are very close to the absolute maximum sinking current rating. I would reduce it to 10mA or less. So change R7 and R8 to 680 ohms
Oherwise, if it does what you want, it must be correct.

[ullisees]

LM393 with relays.PDF (11.8 KB)

I've removed the LED's and added the relays

[jim-p]

Does it worK?

[DaveX]

Shouldn't they be NPN transistors?

[ullisees]

@DaveX

Shouldn't they be NPN transistors?

If I us NPN then the relays are energised when both inputs to the LM393 are equal to each other

[build_1971]

If it is pnp, the load should run from collector to gnd and the emitter should be at vcc...
Are you sure you have it upside down like in your schematic?

[anon27210439]

And for the hysteresis, the feedback resistors should go to the non inverting (positive) input of the comparators.

[herbschwarz]

You can not use PNP transistors in that circuit. With the emitter grounded, you need a negative voltage on the base to turn it on and there is no negative voltage available.

[jim-p]

Does it work?

[ullisees]

@jim-p It does on the simulator. Going to try it properly to see if it works

[jim-p]

Ok.

[johnerrington]

@ullisees

. I am trying to replicate a very old circuit that uses transistors to turn a 6v dc motor CW or CCW depending on what voltage is coming from 2 potential dividers.

Can you show us the circuit?

How to make a schematic you can post.

When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th…

[ullisees]

@johnerrington

Can you show us the circuit?

The circuit is in post 13