Circuit Design Question -- Scale voltage in half
Thread Starter
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
Circuit Design Question -- Scale voltage in half well... my fuel pressure gauge is one of the older autometer full sweep gauges w/the black box...
As such my only reference voltage is 0-12 volts... anyone know how to design a cricuit that would scale the output voltage in 1/2 ?(0-6 volts)
Then I'd also need something so if voltage goes over 5 volts it'd not pass the extra voltage on (Diode?)
As such my only reference voltage is 0-12 volts... anyone know how to design a cricuit that would scale the output voltage in 1/2 ?(0-6 volts)
Then I'd also need something so if voltage goes over 5 volts it'd not pass the extra voltage on (Diode?)
Go to Radio Shack. And buy either an LM117 or an LM317 three terminal 5volt regulator. I'm not sure off the top of my head which one is positive and which is negative, so get the positive one. There will be a pinout diagram on the back of the package. I believe pin 1 is input (hook your 12v line to that), pin 2 is ground (hook your ground to that), and pin 3 is output (hook that to the meter). They are 1 amp shunt regulators, so if the current requirements of the gauge are above 300ma you may want tohook a heat sink to it. There is a hole in the tab to do this. They are about $2-$3 for the regulator.
Dooo, you said reference voltage. The input impedance is a factor but since it is a reference it may be high. So connect 2 4.7k 1/2 watt resistors end to end. On one end connect to the voltage source, the other end connect to ground. The junction of the 2 resistors will be 6 volts +- the tolerance of the resistors. I don't know if there are 5v zener diodes, but there is a 5.1v. Connect the side with the band to the junction of the 2 resistors and the other side to ground. That will shunt any voltage over the zener threshold to ground and clamp the voltage, sort of, at +5.1v.
Dooo, you said reference voltage. The input impedance is a factor but since it is a reference it may be high. So connect 2 4.7k 1/2 watt resistors end to end. On one end connect to the voltage source, the other end connect to ground. The junction of the 2 resistors will be 6 volts +- the tolerance of the resistors. I don't know if there are 5v zener diodes, but there is a 5.1v. Connect the side with the band to the junction of the 2 resistors and the other side to ground. That will shunt any voltage over the zener threshold to ground and clamp the voltage, sort of, at +5.1v.
Last edited by ArKay99; Jan 19, 2005 at 04:28 PM.
Actually the more I think about it, you can likely just use a pair of resistors in a voltage divider without having the buffer of the amp.. Basically just take the two resistors you see in front of the op amp and forget about the chip. You'll want a 1:2 ratio on the resistors -- the one going to ground should be 1/2 the value of the one inline. Use something like 10k and 20k ..
On The Tree
Joined: Feb 2004
Posts: 114
Likes: 0
Originally Posted by Brains
Actually the more I think about it, you can likely just use a pair of resistors in a voltage divider without having the buffer of the amp.. Basically just take the two resistors you see in front of the op amp and forget about the chip. You'll want a 1:2 ratio on the resistors -- the one going to ground should be 1/2 the value of the one inline. Use something like 10k and 20k ..
the voltage devider should be 2 resistors of the same value:
12V
I
\
/ r1=1k - 10k depending on power req.
\
/
I
o--------------o---- 6v
I I
\ I
/ -- r2 = r1
\ /\ 5v crowbar diode circuit in parellel
/ --
I I
Gnd. Gnd.
the resistor values should be 10x or so of the impedance of the guage.
More Than Zero
ps sorry this does not do graphics lol
Last edited by M_T_0; Jan 20, 2005 at 01:36 PM.
Thread Starter
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
Originally Posted by y2khawk
are you trying to modify the sender output from the autometer sender, or make the 5V supply for it?
Modify the sender output so that I can input it safely into my EIO HP Tuners cable...
Trending Topics
umm, the autometer senders are 5V out. I ran a second one for quite awhile to montior fuel pressure via the AC pressure input to the PCM. 5V supply to the sender, 5V out.
Where are you getting the 12V from?? You didn't feed 12V into the sender did you?
Where are you getting the 12V from?? You didn't feed 12V into the sender did you?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo Thread Starter
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
hmmm... I'll have to look at it again... When we were testing a month back or so we couldn't find anything that seemed to be 5 volts ... and I thought I had read somewhere that the older full sweep autometer fuel pressure gauges were 12 volt from the black box to the gauge... I'll have to investigate once it warms up...
Thanks everyone for the input
Thanks everyone for the input