While installing the Empeg in my Miata, I again remembered that the oem radio had the ALC (automatic level control), where the volume would ramp up with speed. The speed is read from a pulsed 12v source (4 pulses per revolution). There are numerous ideas about speed controlled volume around on this board (not all including speed sensors but road noise):

my first thread
a newer one
an older one
and a very old one

I have the wire with the speed pulses right there next to the harness and could try any ideas, solder any provided diagram almost immediately. I see the road noise method as a very valid alternative, but once the speed sensor is input into the empeg, the possibilities just go beyond volume control
So whadaya say? What should I do with my poor lonely speed sensor wire, begging me to use it?

What should I do with my poor lonely speed sensor wire, begging me to use it?

My opinion of what you should do with the wire...

1. Create a "box" with RCA inputs and outputs with an adjustment for the amount of speed attenuation based on the pulse. Don't bother interfacing the speed wire with the empeg, because if all you want is volume control, it's better to do it in an external box. For example, people who run their empeg through an external head unit could benefit from this box, too. And you wouldn't need to modify the software on the empeg to make it work. It would all be analog, in this box. For that matter, an external box could be used by people who own ordinary stereos. Such a box would be so useful, I'm surprised it doesn't already exist as an aftermarket product. If you could make it work, I'd bet you could sell a million of them.

2. Make me a relay interface that will allow me to mute the speaker on my radar detector below 30mph.

Does this pulse wire exist on all cars, and if so, where is it on my 2000 Honda Accord?

Does this pulse wire exist on all cars, and if so, where is it on my 2000 Honda Accord?

Thats a very good question!

.. but i have a miata and dont appear to have this wire! (or if i do then i dont know where it is!)

Do all MX5 / Miata's have this signal wire, and if so how can i find it? What colour is this wire? Where does it come from?

Hope u can help! - If i can find it i'll try and put together some kind of circuit to interface it to the empeg, or maybe a seperate attenuator box (sounds fairly easy to do)...

RichieC

I wish I had the electrical engineering skills to design such a box. I can solder it once someone designs the layout, though

I think all newer cars have a wire like that (most electronic speedo's use it). A complete wiring diagram should display one wire as VSS (vehicle speed sensor), at the least going to/from your ECM (engine control module - computer), if not for varying other uses (speedo, auto trans etc.). The problem in having one box for all cars is that some cars use 8 instead of 4 pulses per revolution. That's why routing it into the empeg would be nice: software control of the pulse reading!

The wire in my Miata is a dedicated wire just for the ALC - and now it's just lying there, bare, unemployed and depressed :P

Besides volume control, one could use the speed info to have the empeg play sounds once you reach certain speed(s), change visuals, calculate distance (if the odometer is broken, or you don't have/want to use your trip odometer) or simply for display.

There is a diagram in one of the threads (or links therein) to convert such a pulse train into a serial format. I'd solder the thing if I knew I had someone to code a program that could use the input (I could use my laptop to check functionality) in the empeg. Any takers?

Edit: Ooops, just noticed Richie's post. Must've come in while I was writing mine. Your Miata only has the wire for the radio, if you had the MPSS or MSSS from the factory (M-Edition cars, C-Package etc.). It's unlikely that you had it on a base model. Nevertheless, dependng on the year, somewhere to/from your ECM you should find the wire with a proper wiring diagram. I found my wire using the Miata MSS FAQ.

What year is your Miata? You can find some wiring diagrams online at http://www.madracki.com/miata/wiring.html.

That'd be awesome if you could design such an interface! Be sure to check out the threads I linked in my post above for some fairly detailed info.

Hmm... interesting...

My Miata (or MX5 as their known here in the UK) is a 1999 (mk2) 1.8iS - not sure what that equates to in the US, i know that there are different models over there, although i think they have similar spec packages...

My car came with a Clarion Head Unit, which was very quickly replaced with a Sony CD player, and later on the beloved Empeg player & Alpine Amp...

The clarion unit diddnt have MSSS or any other kind of volume adjustment, but im just wondering if that speed sensing wire is in the factory audio harness somewhere... i figure it must be to connect to the MSSS Units? or is it a seperate wire? if not then do you know which pin on the connector it is?

Thanks for the info.. i'll check it out and see what i can come up with...

Richie

My Miata (or MX5 as their known here in the UK) is a 1999 (mk2) 1.8iS - not sure what that equates to in the US

That should roughly equate to this diagram. On page 10 (engne performance) I find three wires that I'd check for the right signal. You can also cross-reference that with pin-layouts of your computer (miataforum.com should be able to provide you with that).

but im just wondering if that speed sensing wire is in the factory audio harness somewhere...

it was in mine, but I had MSSS. I don't think your harness has it, if you didn't have ALC.

or is it a seperate wire? if not then do you know which pin on the connector it is?

The link in my last post contains the pin-layout for all MPSS or MSSS model radios in the US miata. That's where I found my wire.

I would assume that it could be done very cheaply. My reasoning is that if GM give you this without any fanfare and put it on all thier radios then it HAS to be cheap and/or easy for them to do it.
I can't imagine GM giving anything away for nothing....

But don't ask me how to build one, I don't have even half a clue