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12-08-2017, 10:37 PM | #11 |
Not Yet Wild
Join Date: Nov 2017
Location: Alabama
Posts: 25
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Re: Project: Display of Speedometer/Odometer + Battery Info
This sounds like a very interesting project to follow.
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12-08-2017, 11:24 PM | #12 |
Gone Wild
Join Date: Sep 2014
Location: Orlando, FL
Posts: 1,308
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Re: Project: Display of Speedometer/Odometer + Battery Info
This sounds like a very nice project. I will follow this as well. I am curious as to why you are not using a shunt that you can depend on? One that has a mounting base. See attached pdf. I think you would have a much more reliable system. 2 cents worth, well maybe 3 cents. See attached pdf, lots of choices.
Last edited by PingEye3; 12-08-2017 at 11:26 PM.. Reason: attach file |
12-09-2017, 01:39 AM | #13 | |
Not Yet Wild
Join Date: Jul 2017
Location: Mocksville, NC
Posts: 54
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Re: Project: Display of Speedometer/Odometer + Battery Info
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12-09-2017, 01:54 AM | #14 | |
Not Yet Wild
Join Date: Jul 2017
Location: Mocksville, NC
Posts: 54
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Re: Project: Display of Speedometer/Odometer + Battery Info
Quote:
I've used this same LCD before and still have one here for testing. It's adequate for me to see at the distance to the dash (with my eyesight I just barely passed my vision test for my drivers license). I'm considering mounting it to the steering column to get it closer but so far I don't see any way to do this without it looking a bit unsightly, plus I won't be able to see it when I'm the passenger. You guys know this will take some time, right? I have to take time out to eat, sleep, watch Oak Island, and maybe some other things. I do these personal projects mostly during the winter when I have a lot of spare time and it usually takes me all winter to do one like this. |
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12-09-2017, 11:38 AM | #15 |
Not Yet Wild
Join Date: Jul 2017
Location: Mocksville, NC
Posts: 54
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Re: Project: Display of Speedometer/Odometer + Battery Info
There appears to be some interest in this project so I'll try to keep y'all posted with the process I'll go through to get to the final design.
First up is to see what the timing demands would be on the CPU chip. With the essential info provided by Sergio, the pulses that must be measured from the tach are coming along at a rate easily handled by most any processor chip. At 40mph it would see around 548 pulses/sec. The pulses would be counted over 1 second and the speed computed and displayed every second. 1 second is a very long time if you're a computer chip. Piece of cake. Next is the math. Using my favorite 2-dollar processor chip (MC9S08SH4) I've got to get creative. It has no floating point hardware built in, and not enough memory to swallow a floating point math package (I don't like those anyway, they're notoriously inefficient). So it took most of last night to factor down the math to its bare essentials. (I've done this before.) I know most of you aren't familiar with binary math but this is what it is. Here are my notes to myself: Calibration: 1. Measure pulses in 165 ft (typically 1539, or $0603 in hex). 2. Shift left 16b. = $0603 0000 3. Divide by 3600 ($0E10). $0603 0000 / $0E10 = $6D70 . This is Scale Factor (SF) as a binary fraction. Computing speed (20mph): 1. Count pulses in 1 second. (At 20mph this typically would be 274) 2. Multiply this by 10. 274 * 10 = 2740 ($0AB4). 3. Divide (pulse count * 2^16) by SF. 2740 ($0AB4 0000) / SF ($6D70) = $1909, or 6409. 4. Shift result right 5b and round. Integer result of $00C8 (200) is mph in 10ths, or 20.0mph. 5. Convert binary $00C8 to ascii decimal string and display on LCD “20.0”. Slow speed (2mph): 1. Count pulses in 1 second. (At 2mph this typically would be 27) 2. Multiply this by 10. 27 * 10 = 270 ($010E). 3. Divide (pulse count * 2^16) by SF. 270 ($010E 0000) / SF ($6D70) = $0277, or 631. 4. Shift result right 5b and round. Integer result of $0014 (20) is mph in 10ths, or 2.0mph. 5. Convert binary $0014 to ascii decimal string and display on LCD “02.0”. Need 32bit by 16bit divide with 16bit result Need 16bit multiply by constant of 10 Next to investigate in detail is the analog part, measuring battery current. Later. |
12-09-2017, 11:59 AM | #16 | |
Gone Wild
Join Date: Sep 2014
Location: Orlando, FL
Posts: 1,308
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Re: Project: Display of Speedometer/Odometer + Battery Info
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12-09-2017, 04:14 PM | #17 | |
MOD of all BS!
Join Date: Sep 2011
Location: Florida
Posts: 17,477
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Re: Project: Display of Speedometer/Odometer + Battery Info
Quote:
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12-09-2017, 04:38 PM | #18 |
Gone Wild
Join Date: Jan 2017
Location: Queensland Australia
Posts: 1,332
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Re: Project: Display of Speedometer/Odometer + Battery Info
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12-09-2017, 04:43 PM | #19 |
Cave Dweller
Join Date: Apr 2013
Location: Always On The Move
Posts: 22,117
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Re: Project: Display of Speedometer/Odometer + Battery Info
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12-09-2017, 06:43 PM | #20 |
MOD of all BS!
Join Date: Sep 2011
Location: Florida
Posts: 17,477
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Re: Project: Display of Speedometer/Odometer + Battery Info
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