Thanks, my mistake...I forgot that we're measuring duty cycle, not pulse width. This forum doesn't have enough smileys, but on another forum I'd be able to use a little animated hand smacking my little animated forehead. ;)

I love driving with this meter. :D

Found another idea. This is an actual DIY Instant/Trip/Average MPG meter that uses input from the fuel injector wire (just like the HF Dwell meter reading injector duty cycle) combined with the VSS (Vehicle Speed Sensor). I don't think it can display fuel injector duty cycle info directly, though.

It's called MPGuino and is based on a DIY kit that sells for under $20. Total cost should probably be under $40.
https://ecomodder.com/forum/showthrea...pace-2115.html

I'll be building the MPGuino shortly. The arduino is in the mail and I just got the lcd today. I should have most of the other parts laying around. When I found out about the arduino, I thought this would be a great use for it. I'm glad someone did more than just thinking about doing it. This should basically be a scanguage for pre-obd2 vehicles from what I understand. Can't wait.

Okay, I found one of my problems with LEDs: Voltage. What's an easy way to reduce voltage using cheap/free parts? I'd like to put in a radiator fan monitor LED, but I'm going to need to cut ~14v to ~3v.

Or, for the fan monitor, what can I come up with that will count seconds while it's on? I'm thinking a battery powered analog watch, maybe...

An LM317T from radioshack is a decent option. Here's a good bunch of info https://ourworld.compuserve.com/homep...den/page12.htm .

Even easier (and possibly cheaper) would be to find either something like a cell phone charger for a car that outputs 3v or one of those universal car chargers and then adjust it to 3v. They should be able to handle 14v I think. Just make sure the amperage is within the range of your LED.



https://photos-d.ak.facebook.com/phot...11627_9941.jpg

Just a few more things before I wire it up. I should be able to make it look decent, but I haven't put much thought into how just yet.

Well, now THAT is a simple and really great solution! I have an abundance of cell phone chargers for a 5v Motorola that has since died. I saved them to hack up for exactly this sort of purpose! They should drive my LEDs nicely.

Come to think of it, they have built-in LEDs. Now THAT is quick and easy!

mpg meter could it be done another way?
 

Hi all. I'm a new member and find these threads very interesting reading.

Could fuel consumption be measured using the following:

Two DC voltages. One proportional to injector pulse width, The other proportional to road speed. The DC voltage for pulse width being done by a gated integrator circuit, And the DC voltage being done by using an LM2907 Voltage to frequency convertor. The two voltages can then be applied to some form of comparator circuit that sums/subtracts etc. To provide a DC voltage that correlates to the fuel being used for the speed (distance travelled).

Would a third reference voltage be needed (equating to the fuel flow rate)?Again all three voltage would need to be compared and an output a DC voltage required to indicate fuel used.

The DC voltage generated could be applied to a moving coil meter, Or an LED bargraph display (LM3914). Obviously the circuit would have to be calibrated. But once the all the DC input voltages have known relative values, calibration of the display device shouldn't be to difficult.

Any further comment or suggestions anyone?

Cheers

Neil