How Analog and Digital Speedometers work

[Shashilostinproj]

Could any one of you help me know how digital as well as analog speedometers work?

 

[j.p.bill]

Analog speedos have a magnet that spins inside a metal cup. The spins comes from a cable that is driven by a gear inside the transmission. The cup is returned to zero by a hairspring, and is deflected by the rate the magnet spins. May be eddy current coupling.

Digital speedos have an input from a sensor that gives pulses at a rate proportional to speed. The MCU counts the pulses for accurate periods, and translates the count into MPH or KPH.

 

[Shashilostinproj]

Thanks bill. That's quite usefull.

 

[Nigel Goodwin]

Except that any modern 'analogue' speedometer is likely to be done electronically by an MCU as well, but just displayed on an electrical meter.

 

[RODALCO]

You can do an easy self check if your analogue speedo has an electronic MCU with a pulse train from a tachogenerator in the gearbox or mechanical with a bowdencable.

When you drive in reverse gear the speedo will record a positive reading on the speedo meter dial and also on the odometer.
If on a bowdencable the speedo needle will remain at zero.
The odo may go backwards or advance as in some types of Smiths and Jaeger meters, with the ratchet drive.

Of course do it somewhere on a quite road or long driveway.

 

[Shashilostinproj]

Thanks!

I did check. It is mechanical with a bowdencable.
Thanks Again