#### Glyn Davidson

Joined Jul 25, 2018
2
Hi all,

I have a 0-5v variable signal. I'm looking for a device that can perform some logic operations. Basically, I want to create a circuit that passes the variable signal without modifying it, except when 0v is received I want to output 2.5v instead.

To give you some background info...

In simple terms, I'm using a potentiometer to control a motor via a controller.
2.6-5v turns the motor in one direction.
0-2.4v turns the motor in the opposite direction.
At 2.5v the motor stops.
This is being operated via radio control.

The problem is that when you turn off the radio control, the motor controller receives 0v which makes the motor go full speed in reverse (and has caused a number of "accidents"). Instead, when the remote is switched off, I want the motor to stop too.

In my mind, it's a simple logic gate that says:

If inputA == 0v Then
output 2.5v
Else
output inputA
End

But I don't know how to achieve this with electronic components.

#### olphart

Joined Sep 22, 2012
114
An easy way is a comparator set for near zero driving an SPDT relay that passes either input or 2.5V.
You'll also want to limit the active input to just above the comparator threshold at max reverse.
Else, if you want max reverse, the motor will stop.

#### ebeowulf17

Joined Aug 12, 2014
3,307
Hi all,

I have a 0-5v variable signal. I'm looking for a device that can perform some logic operations. Basically, I want to create a circuit that passes the variable signal without modifying it, except when 0v is received I want to output 2.5v instead.

To give you some background info...

In simple terms, I'm using a potentiometer to control a motor via a controller.
2.6-5v turns the motor in one direction.
0-2.4v turns the motor in the opposite direction.
At 2.5v the motor stops.
This is being operated via radio control.

The problem is that when you turn off the radio control, the motor controller receives 0v which makes the motor go full speed in reverse (and has caused a number of "accidents"). Instead, when the remote is switched off, I want the motor to stop too.

In my mind, it's a simple logic gate that says:

If inputA == 0v Then
output 2.5v
Else
output inputA
End

But I don't know how to achieve this with electronic components.

What are you using as they receiver? I would expect there to be an output, separate from the 0-5V output, which indicates tuning status. You could use it to trigger a relay as described above instead of using a comparator on the input value - that way you wouldn't give up full reverse capability.

#### Dodgydave

Joined Jun 22, 2012
11,234
Hi all,

I have a 0-5v variable signal. I'm looking for a device that can perform some logic operations. Basically, I want to create a circuit that passes the variable signal without modifying it, except when 0v is received I want to output 2.5v instead.

To give you some background info...

In simple terms, I'm using a potentiometer to control a motor via a controller.
2.6-5v turns the motor in one direction.
0-2.4v turns the motor in the opposite direction.
At 2.5v the motor stops.
This is being operated via radio control.

The problem is that when you turn off the radio control, the motor controller receives 0v which makes the motor go full speed in reverse (and has caused a number of "accidents"). Instead, when the remote is switched off, I want the motor to stop too.

In my mind, it's a simple logic gate that says:

If inputA == 0v Then
output 2.5v
Else
output inputA
End

But I don't know how to achieve this with electronic components.

What output does your radio controller give out, just 0V and 5V, or 2.5V as well?

You're going to need a Window Comparator, set at 2.5V centre, and either side trips your directon relay.

#### Glyn Davidson

Joined Jul 25, 2018
2
Thanks all for your advice. Have solved the problem with an Arduino and DAC breakout board.

#### ebeowulf17

Joined Aug 12, 2014
3,307
Thanks all for your advice. Have solved the problem with an Arduino and DAC breakout board.
Excellent, glad you got it working!