Rebuilding instrument cluster - Page 1
Forum section: electronics / projects

author: somlioy
author_rank: Regular Contributor
timestamp: December 27, 2014, 12:12:59 pm
content: Got an instrument cluster from an old car. The fuel gauge is originally driven by a 0-180ohm float and I want to make the fuel gauge a temperature gauge driven by a thermistor instead. The gauge it self is a galvanometer.You can see the internals of the gauge in the center:So my question is: how can I drive this instrument from an arduino?--This car is being rebuilt with a new engine, gearbox and a transaxle. The original style speedometer is driven by a rotating wire going to the gearbox. The new gearbox doesnt have this, only a output for a pickup or so. My thoughts were to use the arduino to drive a stepper connected to the speedo instead.What would be the best/most accurate way to drive the stepper after the pulse conversions from the pickup have been done? Lookup table, x steps per km/h etc?--Also what circuit protections should I add into my circuit (on the supply side)?

author: SeanB
author_rank: Super Contributor
timestamp: December 27, 2014, 01:23:57 pm
content: Just go and buy an aftermarket replacement temperature sender of the right cold resistance and use in place of the fuel sender. Will work there with no problems, you just have to measure resistance cold and again with it in boiling water ( inside a small plastic bag to keep it dry) and then mark the gauge accordingly. Hot resistance should be somewhere near full scale, so mark the 100c mark as the max temperature.

author: somlioy
author_rank: Regular Contributor
timestamp: December 28, 2014, 01:11:16 pm
content: Thing is I already have the original markings from the original temp gauge. I cant use the original gauge because it's a capillary tube type which doesn't fit the new engine. I got an extra fuel gauge I'm moving over to the temp gauge position with the temp markings instead.

author: SeanB
author_rank: Super Contributor
timestamp: December 28, 2014, 01:25:28 pm
content: So you just want eg a thermistor sensor, probably a generic one that will fit the engine block or radiator. Nissan ones will probably fit. That will drive the existing fuel gauge system correctly, and if you have calibration in mind you just need to measure the cold and hot resistance of the unit, use a variable resistor to get the gauge to read the right levels then pad out the sender using either some series resistors if it is reading high, or some parallel resistors if it reads low till your single point calibration reads correctly. The only need is for a temperature of 90C or so to be shown as in the normal range.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 28, 2014, 01:33:23 pm
content: It is not clear (at least to me) whether you want to drive the original (vintage) indicators on the vehicle, or if you want to replace them with new indicators?All of those sensing scenarios are well-represented by Arduino solutions: Tachometer (engine RPM, ground-speed), temperature, pressure, resistance, voltage etc.If you arrange some new transducer for ground-speed, then you will need to "calibrate" it. Perhaps as simple as using a mathematical ratio of pulse-count to distance, etc.Calibrating a temperature sensor can be as simple as using an ice-water bath to establish 32F/0C and boiling water to establish 212F/100C. Assuming the sensor is reasonably linear between those points (and beyond boiling, etc.)It is easy enough to drive those vintage galvanometers from a microcontroller (Arduino, et.al.) using pulse-width modulation. You will probably need an external transistor driver to achieve the current necessary for that low-impedance coil.

author: Seekonk
author_rank: Super Contributor
timestamp: December 28, 2014, 03:05:56 pm
content: First off, drive the gauge from the Arduino using known PWM values with a FET and get the values for E, 1/4, 1/2, 3/4 F, temp or whatever the gauge is used for. I would power the sensor maybe just through a 1000 ohm resistor from 5V, that would get you over 100 data points which may be enough. The controller common would have to be referenced just at the block otherwise temp would change when the headlights were turned on. You could use a lower value resistor from 12V. One A/D input would have to measure battery voltage as a reference and the other would have to be protected against 12V should the sensor disconnect. The MAP function makes it easy to calibrate the gauge even if it has to be broken into two or three sections. I love those mini boards that cost less than $2.50 shipped!