VWaddict

Cool... -Sounds like a great plan!

Keef

Tom M'Guinn

Well, tonight I confirmed the gauge works perfectly when fed a 0-5 signal through a 4k resistor. It sweeps from left to right perfectly as the voltage goes from 0 to 5. Next up, I need to find a 0-30 psi sensor. Most sensors are MAP, meaning they generate voltage above absolute 0 pressure. I need one that generates voltage once above atmospheric and goes to 5vdc at 30psi. I have an old boost controller sensor like that, but am hoping to find something new.

Bri Bro

Most of the low cost preasure sensors ($30-50) are bridge outputs. To get the desired range, you add a dual op amps and dial in what you want.
Look at the bottom of the sheet in the application section. You could set the output to 0-1v and eliminate the scaling resistors.

A $30 part.
http://www.meas-spec.com/myMeas/down...ltrastable.pdf

A $25 part
http://sensing.honeywell.com/index.c...ment/1/re_id/0

Tom M'Guinn

I was just sitting here sketching out a little circuit for the zeitronix sensor, but I'd still prefer to find a sensor where I can use the full range of the sensor's voltage output.

Chris White

Why bother with a new gauge face? just use the existing one and calibrate it so that the 1 bar is 1 bar of boost instead of 1 bar atmo. I have been playing with this for a while so that I can use the stock gauge with the standalone (electromotive) ECU.
1 bar of boost at the 1 bar factory mark gives you the best resolution on the factory scale.

evil 944t

Chris, Not to go OT and don't take this the wrong way BUT, I can't picture you driving that Mini, lol..

anyways, Good project guys. I will try this with the Link EMS.

Chris White

It confuses a lot of people!

evil 944t

Ha Ha, thats funny, I bet it does. Time to TEC3 and turbocharge that baby!

Chris White

I did put bigger barkes on the front after a weekend at the Glen!

evil 944t

Thats cool, they look like fun cars.

ok, sorry for the OT!!

mikeyoman

Tom... where did you connect the supply ?
I have my dash off at the moment and tried to experiment with what you were trying to do when I first read your post, but nothing happened !
Hope my gauge is still ok as it's been off the car for a year or 2. I used the 2 brass termnials at the rear of the gauge cluster. I did notice that the gauge wiring goes to the Rev counter circuit board before it reaches the boost gauge, then I left well alone.

Tom M'Guinn

I patched in at the red plastic 4 wire connector that connects the engine harness to the dash harness in the passenger footwell, above the DME and KLR. Rather than cutting and splicing wires for testing, I disconnected the connector, bridged the other 3 wires with radioshack spade connectors, leaving the red/white wire disconnected. I then pumped my own signal into the gauge-side harness on the wire that would have been connected to the red/white wire on the engine harness. ...if that makes any sense....

Tom M'Guinn

Well, that's about how I will set it up, since mine will have 15psi where the 1BAR currently is. The markings on the factory gauge are just too vague for my liking. I figured if I marked of 5, 10, 15, 20, 25 an 30, I'd have a much better sense of the boost -- i.e., I could actually tell if I'm at 17 or 19, rather than guessing. The factory gauge is marked like a sun dial.

Tom M'Guinn

Ok, fast-farward 4 and a half years, and I've now got it working. I ended up using an Arduino based controller for flexibility, so I can program it to any scale, etc. Consistent with Brian's findings last time, it appears the factory scale is actually a 0 to 4.5vdc output rather than full 0-5vdc, which explains his .45 volts at 1 bar on the gauge. After reading up on MAP sensors, this is pretty common. Even the zeitronix sensor outputs from 0-4.5vdc, even though it is powered by 5 volts.

At any rate, the video below shows the gauge working compared to a VDO mechanical gauge sharing the same pressure line. The factory gauge is completely de-coupled from the KLR and is just taking the signal from a zeitronix MAP sensor, adjusting it in the Arduino, and sending the calibrated voltages to the factory gauge. Perfect for stand-alone EMS cars, or folks who want to make their factory gauge more useful. For testing, I have it set up to show 15psi at the 1 BAR mark, and 30psi at the 2 BAR mark, but am planning to set it up so that I can select whatever boost level I want at the 1 bar mark (for quick real time confirmation my boost is where I intend for it to be)....

http://www.youtube.com/watch?v=bIoQ9...ature=youtu.be

Tom M'Guinn

Well, one correction to the above. I was able to bench test a spare KLR and found that the KLR boost sensor voltage (pin 5) goes as high as 4.9 volts (rather than the 4.5 I theorized). It seems that 1 bar on the gauge is simply not the exact middle of the sensor readings. It's somewhat academnic because you can fine tune with a trim pot or in the software to have the gauge read wherever you want it at any particular boost level based on whatever sensor you use...