General Technical & Electrical General technical and electrical discussion for the Ford Ranger that does not fit in any other sub-forum.

How does a speedometer work?

Thread Tools
 
Search this Thread
 
Old Sep 6, 2020
  #1  
stRANGER_danger2010's Avatar
Thread Starter
|
Member
Joined: Jul 2020
Posts: 2
Likes: 0
From: Kamloops, BC
How does a speedometer work?

I have owned my 2010 ranger, with the 4.0 and an auto trans. for a while now, and the only thing it is missing is cruise control! I have a fair bit of experience programming with microcontrollers, as well as all the rescources necescary to build parts I will need to build my own criuse control, and make it plents safe enough for operation.

I understand you can buy an aftermarked cruise control but I think it would be fun to build a part of my vehcle on my own, the way I want it.

I will nead to build an actualtor system for the throttle linkage itself, as i dont have an E-throttle, as well as i will need to tap into the brake lights so my system shuts off when I hit the brakes, I will probably need to tap into some sort of airbag sensor so my system will shut off in an accident and I would like to tap into my neutral safety switch also, or just add a microswitch to the shift linkage so my system only operates when the truck is in drive. The last thing i need for my system to work is (obviously) knowing the speed of the truck. For this I want to tap into the signal from the (what i'm hoping is electric) speedometer.

Here is where I need your help!!! common microcontrollers run off of 5v, and take an imput signal of between 0 and 5 volts. I am wondering what the output voltage of the speed sensor does, is it a a fequency that changes as you drive faster or slower, a 0-12v speed dependent voltage range, 12v being the highest number the speedometer reads and 0v being not moving, or some sort of combonation of the two, like a PWM signal, or is it just a straight up mechanical cable.

Ideally I would attach an ossciliocope to the output and see what is going on, but it's pretty hard to drive and use a scope at the same time.

Sorry for the really long post, ive never used a forum before and I'm hoping if someone can help me out!!
 
Reply
Old Sep 6, 2020
  #2  
RonD's Avatar
RF Veteran
iTrader: (1)
Joined: Jan 2014
Posts: 30,635
Likes: 2,952
From: Vancouver, BC
In 2004-2011 Ranger a digital signal is used for instrument cluster, so no analog speed signal there

But there is one, used for cruise control, on the computer in engine bay
It may already be there in the wiring harness
The computer has 3 connectors now, a 70 pin and TWO 50 pin connectors
One of the 50 pin connectors will have a VSS(vehicle speed) OUT, its pin 1 and should be a purple/orange stripe wire, next to a Yellow wire in pin 2

The other 50 pin has no wires in pins 1 or 2
But it does have one in 3rd pin, it will have a Yellow/orange stripe wire, this is the OSS(output shaft speed) wire, it can also be used

Ford uses AC Voltage from most rotational sensors(since 1995), like crank sensor, cam sensor, ABS sensors, and OSS or VSS sensors
Called Variable Reluctance(VR) sensors
These generate their own AC Voltage, but the voltage is not what is used, the sine wave is what is used, and only HALF the sine wave, positive half, so these sensors have a ground reference as one of the wires and the other is the + sine wave pulse, and the pulse count goes up as rotation increases

VSS wire will have 8,000ppm(pulse per mile), OSS maybe 30,000ppm
The OSS is used for shifting, of course, but the computer is also programed with rear axle ratio and tire size, so it can correctly convert 30,000ppm to 8,000ppm needed by speedometer and Ford Cruise Controls
But the 8,000ppm signal is sent over the Can Bus Data network to the Cluster, not on its own wire, like 2003 and earlier Rangers
But Cruise still needed the hard wire so it is there, well the pin is there for it is

BUT................if you are building a cruise from scratch you could just use any ABS sensor as the speed source, they are easy to get to, you could tap one at the 4WABS module in engine bay
Ford did that in 1998 to 2000 Rangers, they used the rear axle ABS as the speed signal and converted it to 8,000ppm with GEM module

A cruise control, any cruise control, doesn't have a clue what MPH is......................so not really a "speed" aware device
What it does is get a pulse that changes, the "speed" signal, when you press SET, then it tries to hold that pulse count, MPH doesn't matter, you set it so you know the speed, but it doesn't care
So you don't need 8,000ppm you can build what ever you want as long as it can "see" the pulses from the source you choose

Most actuators are Vacuum Motors, you should be able to adapt one







 
Reply
Old Sep 6, 2020
  #3  
DILLARD000's Avatar
Member
Joined: Mar 2020
Posts: 850
Likes: 224
From: US
"As the wheels on the bus go round & round, the speedometer on the dash bounces up & down"
It's a mysterious mechanical + electrical device beyond explaination by simple mortal beings.
Sorry it's getting late & I couldn't help myself. Good night.
D
 
Reply
Old Sep 7, 2020
  #4  
stRANGER_danger2010's Avatar
Thread Starter
|
Member
Joined: Jul 2020
Posts: 2
Likes: 0
From: Kamloops, BC
Wow that is more help than I ever could've imagined getting! I will be using every bit of that info and make sure to post some photos of the final product!
 
Reply
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Z ack
General Technical & Electrical
14
Sep 4, 2020 09:53 PM
Jbellracing
8-Cylinder Tech
7
Jun 5, 2020 10:23 PM
#1Dude
General Technical & Electrical
15
Apr 21, 2017 09:05 AM
#1Dude
General Technical & Electrical
3
Mar 11, 2017 02:51 PM
TrePaul86
Audio & Video Tech
3
Apr 3, 2009 11:47 PM




All times are GMT -6. The time now is 08:39 AM.