I am working on a project to build a Digital to analog converter to interface a 0-5vdc square wave 30hz fuel level sensor with an antique dc analog fuel gauge.
Its for a restomod, and I want to use the digital fuel gauge so my PCM can see fuel quantity, but the fuel gauge is original and uses a 12vdc input and a +/- 1.5vdc sensor input.
The digital sensor wave outputs 0vdc for empty, 2.5vdc for 1/2, and 5vdc full.
The indicator input is +1.5vdc for empty, +0.31vdc for 1/4, -0.3vdc for 1/2, -0.75vdc for 3/4 and -1.5vdc for full.
I've coded some arduino for CAN bus control and reading, but this is my first time attempting to build a DAC. I'd like to keep the converter as small as I can.
Any help hardware, coding, general thoughts is appreciated.
That can be done with a cap, some resistors and an Op Amp. The Op Amp is for buffering or gain change if needed.
Capacitor (Cap): Used for filtering in a low-pass filter. Capacitors can help smooth out signals or remove unwanted frequencies.
Op Amp (Operational Amplifier): The Op Amp is used for buffering (to prevent loading the source) or for adjusting the signal amplitude (gain) if necessary. It ensures that the signal maintains its integrity when interfaced with the next stage of your circuit.
R4/R5 control the gain. R6 and C2 form a low pass filter or integrated.
There are Arduinos with a D/A already built in as another possibility.
Exactly, with 10vdc across the primary coil, the gauge goes neutral (middle) then the 2 wires from the fuel sensor create a +/-1.5vdc to drive the secondary coil, and the needle. I'll reply with a picture below:
See post 6 for the gauge schematic, its for an old military aircraft (experimental). So there's a left and right circuit. With Pots to calibrate the gauge.
So Far I have sourced a Bi-polar boost power supply, an OP amp (TSH82), and I have an Arduino uno. My plan is to work up a prototype for bench testing, before I miniaturize the circuit. This is a redundant system, because the Fuel level sensor is primarily going to an interface for the avionics, but I want to keep the existing military gauge working for aesthetic reasons.
Perhaps this is overcomplicated.
You have a 30Hz PWM with an average voltage in the range 0 - 5V.
You have a guage that appears to be moving coil, with a field coil (bobines de champ) to provide the magnetic field, driven by a 10V supply.
Why cant you just invert the PWM with a single transistor, then do this:
The inertia of the meter will do the D-A conversion job of filtering the PWM.
I need to see the full circuit with the transistor you talked about to comment, but I’m also aiming to be able to make a comparison of the fuel level and drive a discrete low for activation of a warning light.
Then circuit in post 6 shows A-B providing the fixed mag field supplied by 10V & (presumably) 0V; and c-e, d-e the signal. The diagram doesnt show a connection between B & E
however the picture only shows 4 terminals.
That wouldnt prevent the "GND" terminal being held at 2.5V if the guage was isolated (or the ground pin isolated form the case, then the V+ supply would need to be 12V or thereabouts.
Without taking the indicator apart, the measured resistance is 700k Ohms forD-E and 670k Ohms for C-E. There are coarse and fine potentiometers for calibration, I will need to take the indicator apart if you need more precise measurements.
Try this: R4 R5 C1 hold B at 2.5V
When BC108 is OFF ( PWM at 0V) A is at 5V so +2.5V across the coils
When BC108 is ON ( PWM at 5V) A is at 0V * (approx) so -2.5V across the coils
OK there will be a small positive, so maybe 0.2V - you can use a POT (say 250 ohm) in series with R2 if you wish to make the reading adjustable.
