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

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rbpowered

Joined Mar 23, 2014
2
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?
 

#12

Joined Nov 30, 2010
18,224
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.
 

inwo

Joined Nov 7, 2013
2,419
A little more info will be helpful.

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?
 

#12

Joined Nov 30, 2010
18,224
Sorry, my sister was on the phone distracting me.:(

TL431 is a suspect in this case, too.
 
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Thread Starter

rbpowered

Joined Mar 23, 2014
2
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.
 

MrChips

Joined Oct 2, 2009
30,714
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:

6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will result in Your thread being closed without question:
• Any kind of over-unity devices and systems
Automotive modifications
• Devices designed to electrocute or shock another person
• LEDs to mains
• Phone jammers
• Rail guns and high-energy projectile devices
• Transformer-less power supplies
This can be found in our Terms of Service (ToS)

Here is a site that may provide you with some assistance: Electro Tech Online

Good luck.
 
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