Lowering voltage question

Thread Starter

Bliepbliep

Joined May 16, 2018
12
Hello
I've a question regarding lowering a voltage.
There's a 5v line incomming.
And I should split this up to 3 different wires.
- 3v, 2v and a 1v wire
My understandings of electronics is very basic. But if I'm right I should use a diode?
But how do I select the right diode?
 

BobTPH

Joined Jun 5, 2013
2,109
What are you going to do with these 3 voltages, i.e. how much current must they supply?

Are they referenced to the same ground as the incoming 5V supply?

Bob
 

Thread Starter

Bliepbliep

Joined May 16, 2018
12

mcgyvr

Joined Oct 15, 2009
5,394
Its unlikely that a diode alone is the "proper" solution...
Usually you would want a proper voltage regulator circuit for each voltage and rated for the current needed,etc...
 

WBahn

Joined Mar 31, 2012
24,973
It's a control unit (ECU)
2A is max.
What is the TOTAL draw of all three circuits? If each is 1 A, then the total is 3 A which exceeds your supplies capabilities.

What are these powering? More to the point, how sensitive are they to having the correct voltage and to noise on their power lines?
 

Thread Starter

Bliepbliep

Joined May 16, 2018
12
I hope this makes it clear.
Forgive me if I used wrong symbols.

There is 5V incomming
There are 3 circuits (with a switch)
When the switch is pressed the controls knows which button is pressed depending on the restance range (that's why I placed resistors after each switch). Tested and it works.
But there's also a difference in voltage.

There is 5V incomming
When no switch is pressed it's 4v.
When switch 1 is pressed it's 3v
switch 2 = 2v
switch 3 = 1v

 

DickCappels

Joined Aug 21, 2008
6,005
Thank you for the correction to my understanding of the problem.

I think that if you use SPST switches and the citcuit to which the output connects is high impedance you will need a resistor to ground, otherwise you will always get 5V out.

To what is the output connected?

Once this is clear we can arrive at a solution very quickly.

Similarly, why is it than when no switches are closed the output is 4 volts?
 

Thread Starter

Bliepbliep

Joined May 16, 2018
12
Thanks for your reply.

It works like this:

The control knows which switch is pressed based on the resistance value.
So for example: switch 2 is 7Ohm. Then the control knows switch 2 is pressed based on the resistance range.

But the control also wants to know the voltage.
We tested the unit with the resistors in place, and it does work. But the control thinks there are other buttons pressed because we didn't set the right voltage for each switch.

The output is going back to the control. Control reads the voltage and resistance.

I think there is another thing before the switches that lowers the voltage by 1v.
 

WBahn

Joined Mar 31, 2012
24,973
What is this "control"?

How does it know which resistor is connected?

What is the right node (the "-") in your drawing connected to?

Where does this "control" read the voltage?

Where does the "5V" come from? It's apparently note just a 5 V source if there is something that is lowering the voltage by 1 V.

If your "control" is measuring the voltage anywhere to the left of the resistors, then your resistors are dragging the voltage down by drawing so much current. This is almost certainly a bad idea.

Which switch goes with which resistor? Is that bottom resistor 6 Ω or 0.6 Ω? Regardless, the switches don't seem to be s1 on top and s3 on the bottom.
 

Thread Starter

Bliepbliep

Joined May 16, 2018
12
How does it know which resistor is connected?
It reads the voltage and resistance. And on this information it knows which button is pressed

What is the right node (the "-") in your drawing connected to?
Back to the control (ecu) unit

Where does the "5V" come from? It's apparently note just a 5 V source if there is something that is lowering the voltage by 1 V.
Control unit sends a 5V
But the switching unit (which we are trying to replicate) has the resistors build in. And something to lower the voltage

If your "control" is measuring the voltage anywhere to the left of the resistors, then your resistors are dragging the voltage down by drawing so much current. This is almost certainly a bad idea.
It's a switch unit connected to the control unit.
There are 2 wires to the switch unit
One goes in with 5V, the other one goes back (- in the pic) to the control unit. And this is where it will measure which switch is pressed.

Which switch goes with which resistor? Is that bottom resistor 6 Ω or 0.6 Ω? Regardless, the switches don't seem to be s1 on top and s3 on the bottom.
Sorry these are
3k ohm
7k ohm
and 15k ohm
Doesn't really matter for now which is S1 and S3.



 
Top