# Help! Is there a way to implement this?

#### lawofsine

Joined Sep 24, 2023
6
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!

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#### KeithWalker

Joined Jul 10, 2017
2,930
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.

#### BobTPH

Joined Jun 5, 2013
8,120
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:

#### lawofsine

Joined Sep 24, 2023
6
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.

#### crutschow

Joined Mar 14, 2008
33,365
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.

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#### lawofsine

Joined Sep 24, 2023
6
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.

#### lawofsine

Joined Sep 24, 2023
6
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.

#### crutschow

Joined Mar 14, 2008
33,365
This is the circuit i came up with using your solutions.
So is it doing what you want?

#### lawofsine

Joined Sep 24, 2023
6
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?

#### crutschow

Joined Mar 14, 2008
33,365
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.

#### lawofsine

Joined Sep 24, 2023
6
If the 3.3V supply is sufficiently stable, that can be used.
Thanks!

#### BobTPH

Joined Jun 5, 2013
8,120
Assuming you micros have ADC’s, you don’t need the comparators, just read with the ADC then determine the state.