convert a siganl from negative to logic 1

[wizpic]

I have a circuit set up as differential input with op-amps running of a -/+5V supply, this is so it can measure current flow in either direction it boosts the voltage from 0-60mV to 0-3.73V and the other part converts the signal to a positive voltage regardless current flowing in and out.
This is working very good but I would like to a - sign when current is flowing out the opposite direction on the LCD to so user that it's having current drawn rather than charging.

So the question is how can I add something that will convert the -0 to 3.73V in to give logic high(5v) and remain logic low (0V) when voltage is + 0 to 3.73 volts. I've attached the first part of the circuit to show how it works
I've looked at the compactor op-amp (only in sim), With a current draw of 5amps and -0.757v on the input of the lm393 the output swings high to 5V, I would like to go lower say 1amp with -0.412V (or even half an amp)I would like it to swing high to 5V, Tried changing the resistor values but still it only swings at -0.757V. See pic below
Is there away to achieve this

 

[chuckey]

Your value for R17 is too low. if you want a +/- output I would feed the voltage drop across R4 into a comparator, this voltage swings +- depending on the input polarity.
Frank

 

[KlausST]

Hi,

make it simple:

at pin3 there is the signal input.
* connect pin2 directely to GND
* don´t use R14, R15, R16, R17

****
A 220nF across R3 R4 makes it more symmetric.

Klaus

- - - Updated - - -

Hi again,

Sorry

My answer was too fast....
You need the negative supply for the comparator.
And an additional diode and resistor circuit to limit the output voltage to positive values only.

Klaus

 

[wizpic]

Hi,

make it simple:

at pin3 there is the signal input.
* connect pin2 directely to GND
* don´t use R14, R15, R16, R17

****
A 220nF across R3 R4 makes it more symmetric.

Klaus

- - - Updated - - -

Hi again,

Sorry

My answer was too fast....
You need the negative supply for the comparator.
And an additional diode and resistor circuit to limit the output voltage to positive values only.

Klaus

Thanks for the information I take it I leave R18 in and could you please advise where I would place the diode and resistor ?
I will have ago at and try it

 

[wizpic]

I think this is how it should be done, I've used an op-amp as the LM393 would not work, In the sim it plays up but in the real world it seems to work, When discharging it display's -8.78Amps and when charging it displays 8.78Amps

so just to make sure does it look correct before I commit to this design ?

Thanks
wizpic