Megasquirt Want to use 1 sensor for logging and a gauge
06-28-16, 01:14 PM
#1
Want to use 1 sensor for logging and a gauge
First, Sorry in advance if this has ben asked, but I couldn't find it.
I have a MS3/X I'm installing in my FC and I am creating a new custom harness.
I've got aftermarket oil presure, oil temp, fuel pressure, and coolant temp gauges. I custom mounted them in the stock location in the gaugue cluster for easy viewing. I want to log these inputs as well, but I would like to avoid redundant sensors.
I assume that wiring both the gauge and the MS to the sender would throw off the readings. Is there any other option out there?
Thanks!
I have a MS3/X I'm installing in my FC and I am creating a new custom harness.
I've got aftermarket oil presure, oil temp, fuel pressure, and coolant temp gauges. I custom mounted them in the stock location in the gaugue cluster for easy viewing. I want to log these inputs as well, but I would like to avoid redundant sensors.
I assume that wiring both the gauge and the MS to the sender would throw off the readings. Is there any other option out there?
Thanks!
Last edited by Sideways7; 06-28-16 at 01:16 PM.
07-01-16, 09:59 AM
#2
Engine, Not Motor
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It sort of depends on both the sensor and gauge.
Don't try to share the coolant temp circuit. The internal circuit in the MS3 (and most ECUs) use the sensor as part of a voltage divider. It puts a resistor in series with the sensor, on side of the resistor on 5V and the other side of the sensor to ground. Then measures the voltage at the junction of the resistor and sensor. Unless you can change the bias resistor value in your gauge, or know the bias resistor value and thus eliminate this resistor from the 'Squirt and use a custom sensor calibration, it doesn't work very well.
Sensors may or may not operate in the same way. Usually they do. If they are 1 wire sensors, you should be able to just connect an analog input to that one wire and see a voltage reading. In this case there is a bias resistor in the gauge, and the sensor grounds to the engine block, with the junction being at the wire from the gauge. You can calibrate the input with aid from the gauge itself.
Except, some one wire sensors are current based and the gauge measures the current draw to ground. In that case, you need to introduce a low value resistor between the gauge and the sensor (like 1 ohm) and connect your analog input to the junction of the resistor and sensor. This will throw the reading off slightly...usually 1 ohm isn't very much.
2 or thee wire sensors are easy. One wire will be ground, the 3rd may be 5V, and the other output. Connect your analog input to the output. If that throws the reading off, use a higher value resistor (10K) in series with the analog input.
Personally I prefer redundant sensors. Provides a handy second reference.
That said in my Cosmo I'm just going to use one of the PWM outputs to drive the stock ammeter as a boost gauge and probably do the same with the stock oil pressure gauge as I'm logging oil pressure anyway. Oops, out of analog inputs now. Guess I'll need that CAN GPIO board.
Don't try to share the coolant temp circuit. The internal circuit in the MS3 (and most ECUs) use the sensor as part of a voltage divider. It puts a resistor in series with the sensor, on side of the resistor on 5V and the other side of the sensor to ground. Then measures the voltage at the junction of the resistor and sensor. Unless you can change the bias resistor value in your gauge, or know the bias resistor value and thus eliminate this resistor from the 'Squirt and use a custom sensor calibration, it doesn't work very well.
Sensors may or may not operate in the same way. Usually they do. If they are 1 wire sensors, you should be able to just connect an analog input to that one wire and see a voltage reading. In this case there is a bias resistor in the gauge, and the sensor grounds to the engine block, with the junction being at the wire from the gauge. You can calibrate the input with aid from the gauge itself.
Except, some one wire sensors are current based and the gauge measures the current draw to ground. In that case, you need to introduce a low value resistor between the gauge and the sensor (like 1 ohm) and connect your analog input to the junction of the resistor and sensor. This will throw the reading off slightly...usually 1 ohm isn't very much.
2 or thee wire sensors are easy. One wire will be ground, the 3rd may be 5V, and the other output. Connect your analog input to the output. If that throws the reading off, use a higher value resistor (10K) in series with the analog input.
Personally I prefer redundant sensors. Provides a handy second reference.
That said in my Cosmo I'm just going to use one of the PWM outputs to drive the stock ammeter as a boost gauge and probably do the same with the stock oil pressure gauge as I'm logging oil pressure anyway. Oops, out of analog inputs now. Guess I'll need that CAN GPIO board.
Last edited by Aaron Cake; 07-01-16 at 10:02 AM.
07-01-16, 11:40 AM
#3
I added 0-5V 10 bar transducers for oil pressure (& fuel pressure) and am using that input and a spare injector output to PWM the stock coolant gauge. It works well. I messed around with the settings so that if my coolant is over 200F, it pegs the stock cluster needle to make me look at the external gauge. Kinda gives you a heart attack, but better safe than sorry.
07-01-16, 08:04 PM
#4
My stock gauges are gone (found some 45mm gauges and completely replaced them) don't have to worry about running them. I also already have a second coolant temp sensor for the gauge, I forgot to mention that.
They are all 2 wire, so I'll play around with the bias resistors. Do you put them in line with wire in the harness, or in the case? Sorry, I have a lot of circuit board experience, just new to the MS.
They are all 2 wire, so I'll play around with the bias resistors. Do you put them in line with wire in the harness, or in the case? Sorry, I have a lot of circuit board experience, just new to the MS.
07-02-16, 09:49 AM
#5
Engine, Not Motor
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If they are two wire sensors and already being run by a gauge, then the bias resistor is already in the gauge. You don't need the bias resistor. Connect the analog input of the 'Squirt to the gauge "signal" wire and see what happens. As long as the gauge reading isn't altered and you see a number at the analog input, you are good to go.
You only need the bias resistor if the 'Squirt is powering the sensor. For example if you are adding a second temperature sensor for an air to water intercooler tank.
Once connected, you can go to Generic Sensor Inputs under Advanced Engine and set the Transformation as "Linear". Then calibrate the 0V and 5V signals until the gauge in Tuner Studio lines up with the physical gauge.
You only need the bias resistor if the 'Squirt is powering the sensor. For example if you are adding a second temperature sensor for an air to water intercooler tank.
Once connected, you can go to Generic Sensor Inputs under Advanced Engine and set the Transformation as "Linear". Then calibrate the 0V and 5V signals until the gauge in Tuner Studio lines up with the physical gauge.
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