I have to get started, here's with what

[arrie]

So now that all my assignments have been handed in, I can relax my head a bit.
What better way than starting something that you've always wanted to do.

I would like to create an air core meter that is driven by using a PIC.
There will actually be two air cores, one for speed, and one for revs.
The revs will be from a pickup from the gearbox, speed will probably be via GPS.
The final product will also have a LCD display for odometer, a digital clock (may be separate smaller lcd) and I'm thinking cabin temperature.

This end product is something that I want to use in my Merc 1729 horse.
I want to use a PIC 16Fxxx, but am worried that it will not keep up.

Has anyone ever experimented with driving air core meters?

 

[arrie]

Oh crap.

Seems to me I'm swimming uncharted waters again.

Does no one know about air core meters or how you would drive them!

 

[dknguyen]

What's an air-core meter?

 

[arrie]

Let's put it that way, if you drive a recent vehicle, there is a chance that your speedo and/or rev counter needles are controlled by an air core.
Real nifty device, rather simple, very few mechanical parts, low failure rate.

 

[Mikebits]

I had to look up what an air core meter is, since I never hear of one, but in my search I came across this.
**broken link removed**

You may have already found this, but just in case you have not I posted the link. It looks like an air core driver IC.

 

[Boomslang]

Without too much effort you can add a dual axis accelerometer to the package to show you the G force in a turn/brake etc.

Why are you going to use the 16F and not the 18F series? An 18F2620 should be more than good enough.

At the moment I am playing around with a 5Hz update rate, 3.3m accuracy GPS, only thing is it can keep the pic very busy parsing all the serial messages.

just some thoughts...

 

[arrie]

Thanks mikebits, I'm aware of that, it's the Phillips chip solution, hard to get here in SA, but it uses two IC's.
The cherry make do with one IC.
I went back to my original notes and distanced myself from the gps speed and odo idea, will make use of the square wave signal from the gearbox.
As trucks are really customized in their gearing, it's rather impossible to calibrate if the original unit has gone bad.
So my idea was to plug in a device running from gps, then compare the two readings and have a software calibration factor that I store in flash to use throughout the process. That also makes life of my PIC a bit easier as it does not run the 1 sec update from gps continually.
But it's still is not that simple.
Boomslang my knowledge of the 18F's are very limited, I had a look at it and saw a difference being the memory block update vs. register addressing with 16F. Since I have done this really long ago, I would like to stick with what I know.
Used to have a little serial based PIC based programmer, but the arrival of WinXP, sort of shorted that principle to bits as Windows have this so called security thing with communicating with serial non-standard devices.
Sometimes it would work sometimes not, more than a headache than anything else.
So I bought the pickit2, but it has not really done work, just played around.

 

[arrie]

Boomslang, which gps make are you using?
What protocol do you use to communicate with it?
Do you actually use it as low as 1 sec update rate?

cheers

 

[DMW]

Sounds like a fun project, i found a sight which you may like:
https://www.mikesflightdeck.com/

hes got some interesting stuff, the RWR [radar warning receiver] is pretty good read too, you want this page:
**broken link removed**


he has several books on sale you can buy, if you do decide to get one, tell us if its any good, i would be interested but for the price tag i cannot afford right now .

where you going to manufacture your own Air-Core or modify a premade one?


edit book link:
https://www.mikesflightdeck.com/mfdbooks.htm

 

[Boomslang]

Boomslang, which gps make are you using?
What protocol do you use to communicate with it?
Do you actually use it as low as 1 sec update rate?

cheers

I am using this one, connected to the PIC with RS232. I use it at 5Hz update rate, but it is easy to make the update slower on the GPS if needed.

 

[Mikebits]

I am using this one, connected to the PIC with RS232. I use it at 5Hz update rate, but it is easy to make the update slower on the GPS if needed.

That is a slick part. I may have to get one

 

[Boomslang]

Yes, it is very "slick"... With the previous GPS I used, the altitude would drift by up to 40 meters, with this one the most I've seen is 2.5m.

edit to add: Reception is also very good, it usually gets 9 or 10 sats while in my house!

 

[arrie]

Boomslang, that really looks good.
What do you pay for it, and where do you buy it in SA?

5Hz, that's like every 200ms. No wonder your PIC struggles to keep up.
I always thought 1sec interval should be fine.
I'm not so much interested in altitude, but could be fun to show the driver how high above sea level he is
I also want to include cab temperature in my little system, should be fun.

The thing is sampling revs and speed from the gearbox can be tricky, speed can by from 0Hz to about 150Hz, not a real biggie.
The revs is a different ball game, 0Hz to about 900Hz. All square wave.
I doubt that everything will be handled by one PIC.
I'm starting with the air core meter, and I am currently scouting for suitable copper wire and a suitable magnet. I think I might get my required 130 degrees with a 5 volt shunt on both coils, so I might pass the commercial air core drivers, and drive them using the PIC with a bit of electronics.
You barely need any amps.

Thanks for the links.

 

[Mikebits]

It is about $100 bucks according to the link. Could you not make the pic ignore some of the updates?

 

[Boomslang]

Boomslang, that really looks good.
What do you pay for it, and where do you buy it in SA?
I bought it from the site in the link.

5Hz, that's like every 200ms. No wonder your PIC struggles to keep up.
That's why I am using 2 PIC's and a math co-precessor.
I always thought 1sec interval should be fine.
1Hz should be fine for showing the speed in the car, but too slow for what I want to do.
I'm not so much interested in altitude, but could be fun to show the driver how high above sea level he is
Yes, that would make a neet "show" feature.
I also want to include cab temperature in my little system, should be fun.
I've only used thermistors before, they are very accurate if you calibrate them properly.

The thing is sampling revs and speed from the gearbox can be tricky, speed can by from 0Hz to about 150Hz, not a real biggie.
The revs is a different ball game, 0Hz to about 900Hz. All square wave.
I doubt that everything will be handled by one PIC.
Reading the signals by using interrupts should be OK for one PIC to handle

____________________________

 

[arrie]

I was hoping there was a SA distributor, but not.
How much did your shipping work out to?
Why a math-co?

Mikebits, I also think updating the rev counter and speedo every 500ms should be sufficient.
All in all, there is too much work for one PIC though.

 

[Boomslang]

The math co makes working with large divisions, cosine, radian conversions etc so much easier... It also has built in support to parse the GPS messages... did not try that yet though.

 

[arrie]

Are you by any chance building a navigation system?

 

[Boomslang]

I'm building an autopilot for my RC airplanes.

 

[arrie]

Boomslang, I've went through my notes when I started looking at this project, I actually started the design and configuration using an 18F2331.
But then I switched to 16F876A. I don't remember the exact reason either.
I'll have to go through the different spec sheets to see why.

At least I have procured my thin copper wire for the sine and cosine coils and seems the magnet as well, it should not cost me too much either.

Hope I will not be charged extra income tax on that score.