# dc variable 4-9 volts to dc variable 0-5 volts

Discussion in 'The Projects Forum' started by rbpowered, Mar 23, 2014.

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1. ### rbpowered Thread Starter New Member

Mar 23, 2014
2
0
I need to build an adapter that will take a variable dc signal that ranges from 4-9 volts and cut it down to 0-5 volts proportionally. In other words, I need to knock 4 volts out of a dc signal. If the input is 4.5 volts I need the output to be .5 volts, input 6.5 volts output 2.5 volts, etc..

Any thoughts?

2. ### #12 Expert

Nov 30, 2010
16,671
7,314
Operational amplifier. Set one input at 4 volts and input the 4 to 9 volts in the other input. The chip will not respond to inputs below its offset voltage.

3. ### inwo Well-Known Member

Nov 7, 2013
2,435
315

It could be as simple as a 4V zener if accuracy is not important and current is < a few hundred ma.

Is this a power circuit or instrumentation?

4. ### #12 Expert

Nov 30, 2010
16,671
7,314
Sorry, my sister was on the phone distracting me.

TL431 is a suspect in this case, too.

Last edited: Mar 23, 2014
5. ### rbpowered Thread Starter New Member

Mar 23, 2014
2
0
Accuracy is very important. My first question is only half of the project.

The signal is coming from an automotive air meter. I'm trying to use a piggyback computer that will only recognize 0-5 volt input. The piggyback ecu will intercept the signal from the air meter to the factory ecu. The meter on the vehicle I'm working on is one of the only ones that does.not output 0-5 or 5-0 volts. It outputs 4-9 volts. It outputs around 4.4 volts on idle and climbs to around 8.6 volts at wide open throttle.

I need to be able to drop the airflow meter signal by 4 volts so the piggyback ecu can read it. Small increases or decreases will be made inside the piggyback and will be output by the piggyback in the 0-5 range. I will then need to increase that output by the exact same 4 volts so the factory ecu will be able to read it.

So accuracy is very important. I really appreciate any help you all can give.

6. ### #12 Expert

Nov 30, 2010
16,671
7,314
Oops. This site forbids automotive discussions. Please try electro-tech-online.

7. ### MrChips Moderator

Oct 2, 2009
12,624
3,451
The owners of All About Circuits have elected not to allow discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

This thread is against the AAC forum rules, Chapter 6, as seen here: