Hi Guys,

noob here.

- I have board A and board B. Both have MCUs.
- I have a reset signal going from board A to board B. The reset signal is normally HIGH (3.3V)
- I have a digital input signal (logic 3.3V) going from board B to board A.
- current implementation is two wires going to board A and B.

My problem is that, is there a way to implement it using only 1 wire?
The condition is that the reset signal should be independent of the state of the input signal because if the reset signal goes low, the whole system resets.
Is there a way to implement this by adding analog/digital circuits to board A or board B?

Thanks!

 

This looks like a homework question. We do not do your homework for you. If you post your best solution, we may be able to help you get it working.

 

Is there a way to implement this by adding analog/digital circuits to board A or board B?

Yes, I suppose you could. But the only reason I would ever do that is if there was no possibility of adding a wire to an existing set of connections.

Here is how you could encode each of the four possible states on one wire as a voltage:

 

Yes, I suppose you could. But the only reason I would ever do that is if there was no possibility of adding a wire to an existing set of connections.

Here is how you could encode each of the four possible states on one wire as a voltage:

View attachment 303535

This looks interesting.. i am thinking this would need at least 4 comparators to decode the four states.

By the way, my solution was to use a sn74lvc1t45 , this is a bidirectional level shifter , will post the schematic later. I am not sure if this would work though.

 

my solution was to use a sn74lvc1t45 , this is a bidirectional level shifter

If I understand, you want to send a signal in both directions at the same time and the sn74lvc1t45 won't do that.

i am thinking this would need at least 4 comparators to decode the four states.

Since you already know the transmitted state at each transmitter near-end, then you can decode the two remaining signal states in the post #3 circuit, with one voltage comparator at each end, to determine the far-end state.
(Note that you have to adjust Out2 comparator threshold based upon the Out2 signal state.)

See the sim below showing the two outputs and the One-wire signals:

At Out1 you can determine the state of Out 2 independent of the Out1 state, if the One_wire signal is above or below 1.5V.

AT Out2 you can determine the state of Out1 if the One-wire signal is above or below 0.5V if Out2 is low, or above or below 2.5V if Out2 is high.

 

thanks for the input guys. your solutions are interesting. i will try to do simulations.

If I understand, you want to send a signal in both directions at the same time and the sn74lvc1t45 won't do that.

ehhh, good thing i have not bought this yet.

 

Here is the simulation. It seemed working theoretically.. thanks @crutschow and @BobTPH
This is the circuit i came up with using your solutions. Inputs are appreciated.

 

This is the circuit i came up with using your solutions.

So is it doing what you want?

 

So is it doing what you want?

Yes , this is what i want.
is there other simpler way to implement the reference voltage of the comparator on the right side?

 

s there other simpler way to implement the reference voltage of the comparator on the right side?

If the 3.3V supply is sufficiently stable, that can be used.

 

If the 3.3V supply is sufficiently stable, that can be used.

Thanks!

 

Assuming you micros have ADC’s, you don’t need the comparators, just read with the ADC then determine the state.