Morning all

Finally managed to go for a drive in the car this weekend. problem is the speedo stopped working.

Had a look last night and it looks like I hit a pot hole or similar and the prop moved up and the magnetic switch got smacked snapping it in half.

The switch is no longer available in this country as it's american. It looks like a small length of M6 stud with two wires coming out of the end which opens and closes as the magnets go past on the prop.

So firstly what is the proper name for this switch? next any ideas where I may get something similar, i take it it's not paired like a fuel sender to the gauge?

Alernatively I've read here a a sensor that detects bolts etc and doesn't use magnets at all. What is this kind a sensor called and do you think I could use this as an alternative to magnets as i think the gauge just needs pulses of on and off.

If Maplin do a suitable magnetic open close switch if anyone here who is more clued up than me could have a look and provide a part number that would be great as I have one just down the road.

Many thanks for any assistance, slightly gutted that it broke on the first drive out but at least i know what the problem is.

Cheers all
Nigel

I you just went to Halfords etc you can buy for about £10 a simple bike Speedo and use the magnetic reed switch from that. I'd open the smashed one first though as if it consists of a coil of wire then it works by inductance as the magnet passes it and that generates a small pulse of electricity rather than a reed switch turning off and on. Both types are generally available on the web in electric shops.

Hi there, what you have is a reed switch, if it only has 2 wires one will go to 12V and the other end into the speedo. You can use any of the sensors available but some of the ones fitted to tintops produce a signal of 5volts. These have 3 wires, but there are ways of upping the voltage using a resistor.

I found that the one you have gives the best result, but means you have to use magnets and getting them to stick to the prop is a problem. Im not sure where to get a replacement in the uk but one came with my Motogadget miniscope speedo (germany) which might sell replacements. They do speak English via email and are really helpfull.

Hi

thanks for the replies. The only thing that i'd like confirmation on is the wiring. Is it still a reed switch if one wire is connected to the speedo and the other goes to earth.

I take it that the speedo is sendinding a small voltage to the switch and counting the number of times it earths?

If that's correct then great I now know it's called a reed switch, would Maplins sell something suitable?

Many thanks
Nigel

had a look on maplins and they don't appear to have anything similar. Any ideas of any other gauge manufacturers who'd sell them. I'm having a mental block morning and the obvious answers just aren't coming to me.

Thanks
Nigel

from your description the sensor could be reed switch or inductive.

the former, as the name suggest, consistss of a spring contact that is closedd when a magnet is bought close.

now I am sure some will disagre but that is ok for a bike - low speed and low revs but not so clever for a car - high rpm, high speed plus in your case multiple magnets? the contacts have a finite life, several million which is probalby enough but I wouldn't use that.

on the other hand it could be inductive, RS sell these switches.

.... but what concerns me is that the prop has trashed one sensor already hence who is to say it won't happen again?

if you have Ford box, then you can buy adapater (£ 15) from Burton to allow fitting of Ford sensor (£ 30 new) but make sure you have space for it. There may be need of some simple electronics - contact me if you go this route - to ensure the signals are compatible to speedo.

Alternative is to make a hall effect sensor - two of us on here have done so; the hardest part is to make the sensor body - mine is from bits of al tube soldered together with a small bearing race.

anyways, back to your reeed switch- maplins sell them.

can you show liniky to the switch or photo of innards - I am sceptical it is a reed switch.

[Edited on 20/1/09 by 02GF74]

"Not available in this country". A familiar phrase for sure. Good luck with your speedo!!

It is most likely a reed switch if it is simply connected between earth and the speedo.

Inductive sensors have 3 wires, as do hall effect sensors unless the earth through the body, which yours clearly cannot. They need 3 sensors as they have a reference voltage applied to them as well as a ground connection and a signal output too.

Have a look on the farnell and RS websites, theres probably something on there.

Cheers,
David

http://www.etbinstruments.com/Sensor_range_select.htm

I've probably got the wrong end of the stick but are these worth a look maybe?

quote:

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Originally posted by flak monkey
Inductive sensors have 3 wires, as do hall effect sensors unless the earth through the body, which yours clearly cannot.

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Yup. Inductive / variable reluctance sensors can be two wires.....

Try slicing the old one in half with a hacksaw. If it's got a coil of wire its inductive if its got contacts it's a reed relay. As already said reed relays aren't the best option for long term automotive use because of the vibrations and limited contact life....

^^^ not to mention response time - yer propy shaft with multiple magnets is whizzing a lot faster than a road wheel (diff ratio) so I won't mention it.

It sounds like the one I have for my Telemetrix speedo. Try Europa spares