I want to create a simple GPS speedometer for my classic car. The current speedometer is in KPH and it should not be changed. I want to place a GPS powered MPH speedometer where the old style analog (simple red digits) clock goes.
All this thing needs to do is get an MPH from a GPS and send out the three digit signal to one of those simple red digit readouts.
The cheaper the better. No versatility needed, since this is really going to be dedicated to doing only one thing, always.
Obviously, 12v is necessary, and an easy hookup to an equally inexpensive old style red digit readout will be wonderful.
-dc buck (stepdown) converter + filtering components appropriately rated for your car’s electrical system. (is it a 12 or 24v system?)
-gps module + antenna with an appropriate accuracy and update rate
-microcontroller to read the nmea data from the gps module and interpret the speed and covert it for the display. You will have to program this functionally.
This LCD is nice, but probably several generations too sophisticated. I am talking about those rudamentary readouts with the numbers made up of a couple of lines, not pixels.
Think 1980’s alarm clocks.
What would be the appropriate “update rate” for a GPS to give a linear response with minimum delay and interruption? What am I shooting for here?
Arduino with 7 segment display and a GPS module. You don’t need a buck/boost. The Arduino will handle 12.8v input and convert for 5 and 3.3v. The GPS modules generally use 3.3.
jrickard:
Arduino with 7 segment display and a GPS module. You don’t need a buck/boost. The Arduino will handle 12.8v input and convert for 5 and 3.3v. The GPS modules generally use 3.3.
Jack Rickard
Thanks a bunch. However, I will need a bit of your help. I apologize for my electrical incompetence.
I looked through the Arduino boards and all max at 5v. Do all of them have the ability to convert 12v to 5v? Will it be able to handle the ignition cranking and fluctuations in an automotive situation? IF not, how do I isolate?
jrickard:
Arduino with 7 segment display and a GPS module. You don’t need a buck/boost. The Arduino will handle 12.8v input and convert for 5 and 3.3v. The GPS modules generally use 3.3.
Jack Rickard
Thanks a bunch. However, I will need a bit of your help. I apologize for my electrical incompetence.
I looked through the Arduino boards and all max at 5v. Do all of them have the ability to convert 12v to 5v? Will it be able to handle the ignition cranking and fluctuations in an automotive situation? IF not, how do I isolate?
How easy are these to program?
Yes, they can handle the 12.8 and cranking. They convert the input to a regulated 5v and 3.3 v They use C++ to program. I think it’s easy. But you need to know C++.
Shouldnt there be an easier way, since the GPS outputs NMEA in Kilometers. Shouldnt there be an easy way to go from the GPS to the 7 segment with a quick arithmetic conversion?
Kph / 1.609344 = Mph
Maybe there isnt. It just seems like C++ is overkill for this.
Well… the problem is that decoding the data from the GPS is not as simple as using a serial to parallel converter since the NMEA output is not just a plain number… thus you need a microcontroller.
C++ could be an overkill but it’s not that difficult to learn for such a simple application. Plus, there is a huge arduino community… so the code part won’t be a problem.
I really think that an arduino is the best way to go… it’s the simplest MCU to use… you don’t need a programmer (it’s programmed throught USB), it regulates to 5V and gives you a 3.3V supply for the gps…
the only easier way to do this is to buy a system already built!!
another thing… you don’t need the serial display… you could use this one http://www.sparkfun.com/commerce/produc … ts_id=9483… it’s only $1.95… and I think arduinos have only one serial port, which you’ll need for the GPS… but I could be wrong since I use dsPIC’s
on the downside… the cheapest gps is $50 plus the antenna (on SF)
If you go for Arduino you can use this: http://arduiniana.org/libraries/TinyGPS/ (based on http://www.maartenlamers.com/nmea/). Personally I would build my own circuit using an attiny or atmega, but in that case you need a programmer of course. And btw, I have a few cheap but very good GPS modules left, check below…
Buy one of those big ol’ 4 inch tachometers, pull the front face and needle off, make your own front face, put it all back together and mount it IN the dash panel. Then drive the ignition input with 12v pulses which vary in accordance to your speed and controlled with an MCU of some sort.
Check at about 6:12 into the video. I drove this tach using a PIC and a MOSFET pulsing a 12v line to the input of the tach. In this video, I used the tachometer as an MPG indicator. I had additional modes programmed into the unit to make the tach read just about anything I wanted, including speed, voltage, MPG, MPG average, temperatures, and so on.
It’s all in the programming…And yes, I know this thread is a bit old. I just came across it today.
