Super MPGuino?

[bobski]

Uh... If it's already 0-5V, why bother with resistors? I mean... I guess a low value would be wise in case the voltage ever spikes above Vz, but that should depend on how much current your zener is spec'd to handle.

I find it a bit odd that the voltages are going down as the resistor value decreases... Where exactly are you measuring the voltage?

[gtkid2002]

I measured the voltages right at analog pin 3 on the 'duino. I can try and remeasure the voltages tomorrow though and not use a resistor.

[nickdigger]

My vss is also 4.7-4.8 ... not quite 5.0v. Good point from bobski about skipping the resistors and just taking the raw 0/5v for your vss input. One thing about that though, is you never know for sure what the speedo is going to give you. I have 2 civics, one gives me 5v (like the service manual dictates), and the other gives me 12v on the vss. Hopefully the 5.1v zener diode will prevent >5v from hitting your duino, but that's something i'd rather risk with a $20 arduino than a $50 mega.

The other thing about skipping resistors: when i was trying different values, the real low one (1k) made my speedo act funny. It was good at low speeds, but got real jumpy over 25mph. My interpretation is the mpguino was sucking too much current from the vss circuit. My present value is 3.3k, and my speedo has been just fine with that, with one exception -- one morning my odo quit turning. 18 hours & 200 miles later, it was working again, and has been ever since. My point being, you want your mpguino be invisible to the rest of the car. If it can screw with the speedo or odo, maybe it will affect (or even fry) your cruise control or ECU.

[bobski]

How about duplicating the backlight switching transistor setup? The current drawn by the base of a transistor like that is measured in microamps. I guess that would constitute amplifying the signal as suggested above.

So, the "digital pin 9" connection would go to your VSS signal, the "LED Power" (collector) connection would go to the 'duino input pin, and keep the 5V connection (emitter).
I suppose a pull-down resistor would be wise... 10K or so, T'd into the wire between the transistor and 'duino, the other lead of the resistor going to ground.

[gtkid2002]

All right, I hooked up the VSS straight to the mpguino, and nothing. Tested it with the volt meter and got 4.6something volts. It was hard enough to get the damn thing off the contrast menu, which makes me think it might be voltage dependent or something. I T'd off all three buttons with 10k resistors and soldered them, with no effect; although I left it unplugged overnight, and I think I got three separate button presses out of the thing, but that was it. Then the buttons stopped working.

It's not even reading the Vss, and the buttons act like they're being pressed when I drag my finger across the large amount of extra pins, which makes me wonder if the architecture is that different or not.

When it's in the car, it's getting 12v. I might make a 9v reg and use that to lower the voltage a bit.

Does NKCelectronics.com: BEST PRICED Arduino boards, Freeduino, IC PCB adapters, Connectors, Pin Headers. FAST GLOBAL SHIPPING sell bad stuff or something? I'm wondering if I might have just gotten a bad device, although I know I can't return it because I soldered it.

I don't think it'll do anything to my ecu, but I also don't think that it needs to be amplified if it's getting so close to 5v at the 'duino.

I'll hook up the Hz meter and see if that could work as my speedometer or something. Who knows, maybe it'll work just fine.

Then again, maybe I'll be making a trip to sears to buy a new meter soon.

UPDATE: Yeah, the car did NOT like not having a resistor in place. My transmission light was freaking out and it kept throwing a check engine code. On another note, my multimeter's Hz setting is only off 10mph when I'm on the freeway. So I get to use that for my speedometer. Still no buttons. I'm gonna ask the people who make the seeeduino if they could post a schematic in .pdf of the seeed mega, and I'll go from there.

[nickdigger]

i got my two seeeduinos 168 from NKC last year, and they seem fine so far. My biggest complaint was they began offering the 328 like a week after i bought the 168's, like they were just waiting for one last sucker to clear out the old models.

I would take your mega offline and benchtest the vss & button inputs. For the vss, stick a jumper wire in the header for Analog0, and touch it alternately to 5v & Gnd somewhere on your mega (in a way you wont accidentally short 5v+Gnd together). Maybe also place the board on some static-free material to minimize that kind of interference.

One of the code mods i did was on the custom screen, to display the raw count of vss & injectors, so i can see whether the inputs are working.

something like this:

void doDisplayCustom()
{displayTripCombo('G','H',instantgph(),'S',instant mph(),
'I','N',tank.injPulses,'V',tank.vssPulses);}

something like that. no guarantees for typos, etc

[gtkid2002]

Nickdigger - Think you could post the code? I'm trying to fight with mine and either I just don't get it or it hates me. I tried just editing the last entry on the first line so it would be

void doDisplayCustom(){displayTripCombo('S',instantmph( ),'S',instantmph(),'I','N',instantgph(),'V',instan t.vssPulses());}

And I keep getting the wonderful error message as
In function 'void doDisplayCustom()':
error: 'instant.Trip::vssPulses' cannot be used as a function

Same thing if I use tank.vssPulses

Is this because I don't have the tank.vssPulses defined?

Yeah, I really know nothing about code.

[bobski]

Originally Posted by gtkid2002

Yeah, I really know nothing about code.

The other reason I'm working from scratch: The MPGuino code-monolith. I would rather build my own than try to wrap my brain around all that foreign code.

[nickdigger]

The code i'm using wont help you, since mine is a massive rewrite.

You want to use "tank.vssPulses", not "tank.vssPulses()". The "()" indicate that it's a function, which it is not; vssPulses is merely a number (unsigned long). You also don't want instant.vssPulses either, as it will reset to 0 every 1/2 second.

In your quote, you also are displaying instantmph() twice. Not a killer, but not useful edit: probably a typo in your post. if it was actually in your code, it would have produced another error, which you didn't mention.

[gtkid2002]

Eheh, weee. I get to learn how to write custom code then. No complaints there at least.

Sounds like custom code is the way to go anyways. And thanks Nickdigger for pointing that out, I didn't know it made it appear as a function P:

Any clues on why the buttons won't work? It's also not picking anything up on the VSS with the code modification. Think I just got a defective 'duino?


I'm just gonna try and strip down everything to just the speedometer and build up from there. See how that goes I guess. For the time being, I get to use a cheap multimeter as a speedometer. Awesome, huh?