TruckinGeek

Hello!

Let me start by saying "Wow" what an amazing site! For the last 21 years I have been operating a semi truck (Lorri for my UK Pals) all over north America. As we all know, anything that moves breaks. As a matter of time, cost or convenience I have learned how to do many things on my own from engine repair to electronic troubleshooting.

As a stress relief I have found myself tinkering with various electronic board projects and have now decided to make a couple of items from my own imagination to make my life easier... but I need help!

I shall list my abilitys as best as I can...

1. I can read schematics.
2. I have the tools and talent to make my own 1 or 2 sided boards.
3. I have to ability to program EEproms and some AVR's
4. I can solder the wings of a Nat (Small insect) together. Ie BGA's and SMD are no problem... (Just need to get my "Good" glass's out).
5. I am computer literate.
6. I am patient.

I cannot (at this moment) do any AVR code assembly.

So...
I am looking for input/advice on a small project.

Currently most semi-trucks in north america ride down the road on an "air ride" suspension. It is common practice to take and cut one of the airlines coming from the suspension and insert a "T" connector so that an air gauge can be installed. When looking at the air gauge it is possible (with a little math) to come up with a very good "guess" on how much weight is on your truck. I would like to make it a lot more accurite.... and quicker.

Current Practise:
When Trailer is empty I have a gauge reading of 28 PSI. Since I have two axles connected to this gauge I divide 28 psi by 2 which equals 14. I multiply 14 by 1,000 and I now know that my "Tare" weight of the trailer is 14,000 LBS.
When I put a load on the trailer the PSI goes up in the suspension therefor it goes up on the gauge. So if I look at the gauge when loaded and it reads 78 PSI I divide it by 2 then multiply by 1,000 to get a rough quess of 39,000 LBS gross weight.
I then Subtract my "Tare" weight from that to come to a "Net" weight of 25,000 LBS.

I would like to take an air line (pressure varies from 0-80 psi as more weight is put on trailer)and connect it to a transducer, converting the physical input to an variable electric signal.

From the transducer I would like to go to a trim pot so that the device can be calibrated, then into a ATmel based Micro. With the output from the Micro going to a Easy to read LCD Screen.

Insert above device into a weatherproof casing. Mount on trailer.

Desired Result...

1. The ability to look at a screen and see immediatly what the "gross" weight of that axle is.
2. Push a button (or look on another line on same screen) and see what the "Net" weight is.

Options:

1. Push button to switch from metric to imperial readings.
2. Wireless transmition to hand held LCD device to see same readings but from "Deck of trailer or Cab" of truck.


Limits and or Standards:

1. 12 volts DC is the maximum power available for truck mounted device.
2. MUST be tough. This device will work in a very demanding enviroment weather wise.

Dream Options:
1. Would like to incorperate an onboard wireless tire air preasure monitoring device.

There are devices along this line of thought on the market already. I for one reason and another do not like the products. Besides... I would like to be able to say "I made it" when some-one asks where I got it. If anbody is interested in making suggestions or feels up to helping me learn how to write code for the Micro I would love some input.

dknguyen

What pressure range is required to measure the pressure in the suspension? I think it's beyond the pressure range of any of the pressure transducers I know of. But since you work there you probably already know of some transducers.

You can use Zigbee modules ($30 each for the lowest range option of 100m, which is way WAY more than what you need). They act as transparent UART cables so it's like they're not there at all. I don't think they could withstand sitting outside though in the suspension of a truck.

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TruckinGeek

I have some Mediamate transducers already that I have been tinkering with. Specs- http://www.intertechnology.com/Honey.../MediaMate.pdf

Are outside links allowed?

The input air pressure is between 0 and 80 psi.

The device itself will be mounted on the frame rail of trailer, out of harms way.

ronsimpson

I have driven ‘farm feeder’ trucks that have transducers under the box. It measures 4 tons to within a pound. I don’t know who makes the device but I will look.

Your idea of measuring air pressure should work. In a microcomputer you can add the results of 4 sensors.

dknguyen

*Gasp* I just noticed you said you can solder BGAs? LIES! No one can solder BGAs!

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TruckinGeek

ROFLMAO....

THAT is what I thought for a awhile as well. Then I picked up a Hotair Station. I find that reballing the little beasts is the hardest... O WAIT, positioning them correctly on the board is a brute as well.


Ron: That is exactly what got me to thinking about this idea.

Nigel Goodwin

A friend of mine does as well, you need a few grands worth of gear (and considerable skill) - he actually replaces them in digital satellite receivers.

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TruckinGeek

Satellite receivers you say?... Humm what would a fella who travels down the road for a living need a rather moible source of tv for? Cough, Cough

Here in Canada, Micheals Craft Stores sell an Emrossing hot air machine that with a bit of practise can be used for BGA's. Cost=approx $35.00


Here is a pic of the board layout I am working on.

Attached Images

Board Layout V1.jpg (30.9 KB, 12 views)

TruckinGeek

Ok here comes some the questions... feel free to jump in anytime.

1: Desired effect: Device can run upto 4 hours AFTER main power supply is shut off.
Therory: Just add enough caps (Size and Voltage to be determined after power need and drain is determined) inline after Vreg.

2: Desired effect: Take one varitable voltage input and have it processed by the Micro to give 4 independent answers.

In regards to the micro, would an AT90S2313 do the job? Or would an Atmega 128/256 be better?

Does a trim pot need to be inserted to calibrate signal from transducer or can this be done via Micro's code?

Can I get the Atmel to process 4 requests?

dknguyen

You can use a pot to calibrate the transducer directly (maybe, depending on the transducer).

You could also just do it from purely from code using hard-programmed adjustment factors or constants, or use a button that lets the microcontroller know the current pressure being measured is X pressure so it can calibrate around that (if you are able to apply a known pressure in the first place), or use the pot as a voltage divider to feed the microcontroller's ADC a variable voltage to calibrate it that way- not a direct calibration, but more of a "you're off by this much" signal to the microcontroller so it can digitally adjust for it.

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TruckinGeek

You have just sent me down an interesting road of thought.....

Realistically I can go to a public scale and weight the trailer one time to get a "Known" tare weight and go from there. BUT! It would be nice to have the micro find its own “Tare” weight when empty of freight. I constantly add and remove equipment (chains, straps, wood and friggin snow) to this trailer. To be able to calculate the “Tare” weight right on the jobsite would be a HUGH plus.

JimB

I have no thoughts on the weight gauge at the moment, but I am very impressed with the project specification.

What a refreshing change from "pls give me circut, most urgent".

JimB

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Nigel Goodwin

Sounds really good for attempting to replace large BGA chips, costing over $100, on multi-layer tightly packed PCB's

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

TruckinGeek

Ahh err..... NO!

Kinda handy for those devices you mentioned your buddy playing with though.

3v0

I would use the micro to make all adjustments and calibrations. Prior to loading the truck push a button to have the computer record your empty weight. That will account for whatever non load weight you have added. It will also take care of drift (if any) in the system.

In regards to what processor to use. Unless I missed somthing there is no great need for speed with this system. The AT90S2313 only has 2K of flash. It could work but I would be more comfortable with more memory. Use a chip with at least as many analog inputs as you need. uC's are inexpensive, spend an extra $5 and buy youself some headroom.

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