PICAXE --> HUD Interface

[Fowkc]

Hi Guys,

In this thread: <A href='http://www.rev-ed.co.uk/picaxe/forum/Topic.asp?topic_id=5689&amp;forum_id=29&amp;Topic_Title=Bike%2Bcomputers%2B%2526amp%253B%2BPicaxes%2521&amp;forum_title=No+new+posts+please%21+21' Target=_Blank>External Web Link</a>
Stan used a PICAXE to &quot;fool&quot; a bike speedo to display numbers by feeding it the right pulses.

In the same vein, I should think it's possible to do something similar with these car HUD units:
<A href='http://cgi.ebay.co.uk/LED-Heads-Up-Speed-Display-HUD-MPH_W0QQitemZ170113539290QQihZ007QQcategoryZ36681QQssPageNameZWDVWQQrdZ1QQcmdZViewItem' Target=_Blank>External Web Link</a>

Designed to run off the car's speedo. Trouble is, I don't drive and have little idea what kind of input these would expect. Is the output from a modern car speedo just a square-wave train from the driveshaft (so a few thousand RPM?), or something more complicated?

I can think of many uses for a cool HUD unit, but I'm not spending &#163;50 on one unless it's PICAXEable!

 

[leftyretro]

From the listing:

&quot;It only needs a power and earth connector to fit. It is easily calibrated to suit any vehicle and wheel size and once fitted requires no maintenance or re-calibration.&quot;

Requiring only power circuit it's not clear how this unit senses speed. Perhaps it's much more sophisticated then one might imagine. Anyone know how these work?
Lefty

 

[papaof2]

The only &quot;power and ground&quot; speed sensor I know of is a GPS. Maybe they've built the application around one output from a GPS chip?

That sounds like a good PICAXE project ;-)

John

 

[Fowkc]

Hmm, that's odd, because the other listing (which looks like exactly the same unit):
<A href='http://cgi.ebay.co.uk/HEAD-UP-DISPLAY-UNIT-HUD-DISPLAYS-MPH-ONTO-WINDSCREEN_W0QQitemZ160120709318QQihZ006QQcategoryZ10404QQssPageNameZWDVWQQrdZ1QQcmdZViewItem' Target=_Blank>External Web Link</a>
does specify a speedo connection.

Yeah, from a quick search around the net, I think that first eBay listing is misleading, and these things DO need a speedo connection.

So, what does a speedo output look like, if I want to replicate it?

Edited by - Fowkc on 28/05/2007 11:40:44