How to Convert Car Speed Pulse Signal to Digital Display for DIY Heads Up Display?

Hello,
For my first venture into electronics, I messed around with some LEDs and had a blast. Now I want to do something even cooler. I want to build my own heads up display for my car. Basically, I would have a display shine the speed onto the inside of my windshield.

After some research, I have found that there is a speed readout wire in my car that I can tap into. It pulses twice for every MPH. So, 120 hz would be 60 mph... assuming that I am understanding everything correctly.

So, I can tap off of that for the speed and then get 12vdc from the ignition and ground.

How do I convert the pulse signal into something that can work with the display? I assume that I will need a d/a converter and then half the result somehow, and then send it to the display, or something like that?

I'm not great with the terms or concepts so any help would be appreciated. Thanks!!!

The conversion from pulses to speed is pretty easy -- all you need to do is count the number of pulses per second. This function is called a frequency counter, and only a few ICs will do the job just fine. You can even just divide your pulse input by 2 with a flip-flop (so that 120Hz/2=60Hz) for direct speed reading. No analog conversions required. A quick search should turn up a lot of simple circuits for this, with LED display output.

Getting the display visible on your windshield is a little more tricky. LEDs have to be very bright to overcome sunlight on a bright day, so high-intensity displays are needed. Luckily, dimming those LEDs is easy (reduce the drive current), so they won't blind you at night. A piece of half-silvered mirror (there are probably coated plastics that will do this job) will reflect the display at you while allowing the road to be visible through it. Getting the angle right will take some experimentation.

Sounds like a fun project. There are a few high-end cars out there with this feature. A visit to a showroom or two might provide some ideas.

Awesome! I will do some research and experiments based on your input and report back. Thanks again!!!

As the previous comment said you need to count pulses. However, since you will have a microprocessor to drive the display you should just use a spare input. Almost all microprocessors have counters built in. If you are using a dedicated heads up display and don't have access to the processor code, I'd still use a small micro. It would be about the same price and much easier to configure and adhjust if you had an in-circuit-programmable (ISP) device.

You would need a micro, a ceramic resonator for a clock ( it would be more accurate than you need) and an input interface. I'd use an optoisolator. An. AC input optoisolator would be proof against negative transients on the input (stuff in cars is usually pretty noisy).

A little micro would be one way to do this, but is unnecessary, since all the parts needed can probably still be found at Radio Shack. (You certainly don't need a micro to drive a couple of 7-segment LEDs.) There would be a lot _more _parts, but I figured that the person asking the question was ready for that. At least he wouldn't have to learn how to program, buy a development kit and programmer _as well as _design the HUD hardware.

I'm confused - I thought the question concerned designing a heads up display, not a 7-segment display. Further, I'd still go with a small micro - they're a buck or two and you don't need separate, counters and seven segment drivers. It's also bunches easier to configure. I've designed hardware solutions. Even with wire-wrap, which you can't hardly get anymore, changes are a real bother. Of course, if all your designs are perfect out the gate, that's not a problem. Converting pulses to rpms takes some hardware and changing hardware if it's not scaled perfectly the first time is a bother. It's also difficult to add smoothing and such. If the rpm is just between 1999 and 2000 you may not want the display to flicker between 19 and 20. That takes bunches more hardware.

I am looking into this method too. I would love to use fewer, better elements in teh design if possible. So, I like the micro idea. Going to be a bigger learning curve I think though! Thank you Mark and Stephen!

Think of projection Tv and you have your answer
Whats the other method you could use but more difficult but would work really well

Inside the 02

Lazors, Maybe, Scanning Maybe ,same as a TV 625 lines per frame interlaced 60 frames per second Think 02 Arena think display inside there..... Think amatuer radio slow scan TV Better still Think VHS format Think Video head switching Think helical scan Now its getting interesting Think black and white picture pixels and how you would switch on and off led One led to scan one line now think 625 lines each alternate line on one scan helical imagine it slow motion first to get the idea

What else lets see the propeller clock another good example only think one half revolution instead
http://www.luberth.com/analog.htm but think in terms of horizontal scanning instead (POV = persistance of vision )

http://www.google.co.uk/imgres?imgurl=http://...LdUbGSIumO7AbwlIDYDg&ved=0CGIQ9QEwAw&dur=4688

Armin Van buren in concert seen his stage for his DJ equipment Its a must see Its a somthing I want to do and see (thats what I dream about ) biulding the electronics behind that stage nevermind the car display


http://bwongtech.blogspot.co.uk/2013/02/how-to-build-hud-for-your-car.html
http://hackaday.com/2013/04/05/snowboard-gogg...-critical-data-while-falling-down-a-mountain/

The crom dom story Make dam site more money out of it than you will an HUD put it that way

http://www.google.co.uk/imgres?imgurl=http://...bdUcuwC62X7Qac4oDQBg&ved=0CFcQ9QEwDA&dur=4760

small towers in the center not a very good image but look behind it and you will see through it

Then if you interested see this
http://www.sun-tec.ch/assets/s2dmain.html?htt...02307958f1322504/502307958f1345514/index.html

This then becomes even more interesting because now we can incorporate OLED into glass making Yes ....... Shop windows display advertising inside the double glazed or sandwiched btw the glass panels

Although Ive been told Very silly idea I suppose it is people break and smash windows dont they ! Nevermind I guess we have to shut all the shops down then not much choice cant afford to stay in bussiness with this type carry on "Great shame really such a good idea too "


http://www.architects-paper.com/en/technische-tapeten/led-tapete/

Make your own Oled on glass

http://hackaday.com/2010/03/17/make-your-own-oleds/

Hi Tim, as you have indicated that you are new to electronics, I am suggesting a very simple method to start off with.
(You can make everything more complicated as you progress.)

After the divide-by-two circuit, feed your output into a digital tachometer with LED readout, which will sit inside your windscreen. A small mirror then reflects the image up to the glass. (Mirror is required to re-invert image.)

For example: LED digital tachometer on Ebay:
http://www.ebay.co.uk/itm/Digital-Motor-Tacho..._Measurement_Equipment_ET&hash=item3a7f1ae193

(This type of unit will only work up to 9999 mph, but that's enough until you fit your car with warp drive.)
(Not recommended for engines below 18GW.)

As Mark mentioned, this may be a little dim for use in daylight, but it will provide a starting point for further experiments.
_ _ _ _ _ _ _ _ _ _ _ _

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