Inaccurate Tachometer?

[infernosg]

Originally Posted by infernosg

I'm halfway there. The tach is now being run by a Haltech but I'm still using the stock speedo cable until I rig something up for a Hall effect sensor or the like. Too bad I didn't jump on those trigger wheels being sold a while back. I'm not sure about a digital display but one day the car will have a custom instrument cluster.

I'm now working on the custom gauge cluster. I'm using analog gauges and the tachometer is still going to get its signal from the Haltech but I need to identify a source for the speedometer. I can theoretically use any signal for the speedometer as long as it produces between 4000 and 200000 pulses per mile. Some options I'm considering:

1. Keep the mechanical speedo cable and isolate the speed output from the stock cluster and use it as a signal source.
2. Hall effect sensor + trigger/magnetic pickup wheel on the driveshaft (there are some pre-made options out there that look like they'll work).
3. Hall effect sensor + trigger/magnetic pickup wheel on a front wheel hub (a la TII ABS sensor)
4. Use FD VSS (will this even work in a N/A transmission?)

Thoughts?

[Whizbang]

you could likely reuse the ABS sensor. It puts out a steady signal. just take it from one of the front hubs (that are equipped)

we used that for some rally computers

[infernosg]

Originally Posted by Whizbang

you could likely reuse the ABS sensor. It puts out a steady signal. just take it from one of the front hubs (that are equipped)

we used that for some rally computers

Only problem is I don't have a TII or a ABS car so I'd have to find all that. Is it possible to get the trigger wheel and/or sensor separately and mount them on a non-ABS hub?

[Whizbang]

probably easier to just replace the hub. GXLs with it are common enough.

[infernosg]

Originally Posted by Whizbang

probably easier to just replace the hub. GXLs with it are common enough.

Yeah, I priced the steering knuckle, ABS sensor, and trigger ring new from Mazda and the total is ~$750 for one side. Car-part.com shows a bunch of ABS hubs for pretty cheap so I'll make some phone calls when the time comes.

I did some research on the ABS sensors and it looks like they're variable reluctance (VR, magnetic pickup, passive, etc.) so it's simpler than a Hall effect setup but not as good. Now if only I can find out how many teeth the ring has.

[C. Ludwig]

I believe there is a shop that makes a Hall effect speedo drive that swaps in the TII trans. Forget the name. Search on the evil forum. It may work in the NA trans.

The FD and Miata trans senders use a VR sensor. If one swaps to the NA trans it would work with an A/D converter.

There is nothing really better about a Hall sensor. VR sensors generally are preferred for something like wheelspeed where there is a high resolution target. Just need an A/D converter for your gauge and ECU that want to see a square-wave input.

[TitaniumTT]

Originally Posted by infernosg

I'm now working on the custom gauge cluster. I'm using analog gauges and the tachometer is still going to get its signal from the Haltech but I need to identify a source for the speedometer. I can theoretically use any signal for the speedometer as long as it produces between 4000 and 200000 pulses per mile. Some options I'm considering:

1. Keep the mechanical speedo cable and isolate the speed output from the stock cluster and use it as a signal source.
2. Hall effect sensor + trigger/magnetic pickup wheel on the driveshaft (there are some pre-made options out there that look like they'll work).
3. Hall effect sensor + trigger/magnetic pickup wheel on a front wheel hub (a la TII ABS sensor)
4. Use FD VSS (will this even work in a N/A transmission?)

Thoughts?

Originally Posted by C. Ludwig

I believe there is a shop that makes a Hall effect speedo drive that swaps in the TII trans. Forget the name. Search on the evil forum. It may work in the NA trans.

The FD and Miata trans senders use a VR sensor. If one swaps to the NA trans it would work with an A/D converter.

There is nothing really better about a Hall sensor. VR sensors generally are preferred for something like wheelspeed where there is a high resolution target. Just need an A/D converter for your gauge and ECU that want to see a square-wave input.

I believe its called Speedometer solutions in MN or WI or somewhere around there. They have a unit (or they did anyway) that will thread into the tranny where the cable did. It outputs a hall effect signal that just about any aftermkt speedometer will read an interpret. Cost when I bought it some 7+ years ago was like $75. Worked really well for me until I went full traction control and needed inputs from all 4 wheels. This option will give you driveshaft speed which will get interpreted as speed.... not useful at all for traction control.

[infernosg]

Originally Posted by C. Ludwig

The FD and Miata trans senders use a VR sensor. If one swaps to the NA trans it would work with an A/D converter.

There is nothing really better about a Hall sensor. VR sensors generally are preferred for something like wheelspeed where there is a high resolution target. Just need an A/D converter for your gauge and ECU that want to see a square-wave input.

I'd love to get my hands on a Miata VSS. The N/A RX-7 transmission is nearly identical to NA and non-Mazdaspeed NB Miata transmissions (I have the Miata guts in my transmission to prove it) so I imagine it would bolt right in.

I forgot all about the A/D converter. The speedometer I have says it can use a signal from either a VR or Hall effect sensor as long as the signal is 3V peak-peak. I'm sure the VR input would be slightly irratic if not wired absolutely perfectly so the A/D converter is probably a good idea nonetheless.

Originally Posted by TitaniumTT

I believe its called Speedometer solutions in MN or WI or somewhere around there. They have a unit (or they did anyway) that will thread into the tranny where the cable did. It outputs a hall effect signal that just about any aftermkt speedometer will read an interpret. Cost when I bought it some 7+ years ago was like $75. Worked really well for me until I went full traction control and needed inputs from all 4 wheels. This option will give you driveshaft speed which will get interpreted as speed.... not useful at all for traction control.

I did a quick search on the other forums and found a few hits. Latest seemed to be from 2010 and the mentioned cost was ~$100. Considering that's less than a new Miata VSS or a used ABS hub and it wouldn't require a A/D converter it's worth a call. Do you have any pictures of the unit you had or any knowledge of the pulses/revolution?

[infernosg]

Originally Posted by infernosg

I did a quick search on the other forums and found a few hits. Latest seemed to be from 2010 and the mentioned cost was ~$100. Considering that's less than a new Miata VSS or a used ABS hub and it wouldn't require a A/D converter it's worth a call. Do you have any pictures of the unit you had or any knowledge of the pulses/revolution?

In case anyone is curious I spoke with Speedometer Solutions yesterday and they still offer the converter. It attaches right to the stock mechanical speedometer driven gear housing and generates a digital square wave signal with 16 pulses per revolution. Three-wire hookup: switched 12V power (red), ground (black), and signal output (white). $98.50: