Hello,

Before I get started I must admit that I know very little about circuit design beyond what I have studied through this forum.

I am working on a project for a car that I am restoring and hope you can help me out.

The project:

Use the signal wire from my speedometer sending unit to set off a simple LED sequence that increases in speed with the vehicle speed.

The components:
The signal wire sends a hall effect pulse at a rate of 8000 pulse per mile. The vehicles power system generally runs at 14.5v. There will 9 total LEDs that need to flash in groups of three. When the sequence starts group 1, will flash, followed by group 2 and then group 3.

Ideally, the sequence would take about 1 second to flash a 0 MPH and look solid at roughly 70 MPH.

My soldering skills are acceptable and I have started to learn how to read a circuit diagram. If this is more complex than I think it is I also am willing to offer up a commission, donation, or skill swap. Please PM me.

Thank you in advance for your help!

Oh yeah, and of course I will post pictures and video when complete!

 

A Frequency to voltage converter IC, with the output feeding a bar graph driver would work.

There is another thread here by StealthRT concerning a tach signal for a remote start that is very similar.

 

A Frequency to voltage converter IC, with the output feeding a bar graph driver would work.

There is another thread here by StealthRT concerning a tach signal for a remote start that is very similar.

Thanks! That looks very doable. One quick question. The output on StealthRT's circuit, is it either on (0v) or off (5v), or will it move between those two voltages as the pulse speeds up?

Also, hopw would you suggest I use that signal to drive an LED sequence? <edit> NM... I found both the LM3916 which looks like it will work.

 

The output of the "Engine Running" circuit was designed by SgtWookie to be on or off using the transistor.

The analog output to scale is from the IC, which could drive a voltage dot/bar driver IC for your application, or even cascade a couple of them for a full range moving dot/bar.

Combining the circuit at the top of Page 7 from the Frequency-Voltage Converter 2907 IC to 3 stacked/cascaded LM3916 dot/bar drivers would allow 0-30 LEDs to be lit, or a single LED to move between 0-30 positions.

Scale 1 LED = 4mph, and it would make a quick visual 0-120mph speedometer in dot mode. Of course, nobody drives that fast, so scaling 1LED = 2mph would be more sane, for 0-60 display. Maybe switch from bar mode in daytime to dot mode when it is dark?

Just tossing out ideas, and now I'm thinking about building one for the bike.

 

The output of the "Engine Running" circuit was designed by SgtWookie to be on or off using the transistor.

The analog output to scale is from the IC, which could drive a voltage dot/bar driver IC for your application, or even cascade a couple of them for a full range moving dot/bar.

Combining the circuit at the top of Page 7 from the Frequency-Voltage Converter 2907 IC to 3 stacked/cascaded LM3916 dot/bar drivers would allow 0-30 LEDs to be lit, or a single LED to move between 0-30 positions.

Scale 1 LED = 4mph, and it would make a quick visual 0-120mph speedometer in dot mode. Of course, nobody drives that fast, so scaling 1LED = 2mph would be more sane, for 0-60 display. Maybe switch from bar mode in daytime to dot mode when it is dark?

Just tossing out ideas, and now I'm thinking about building one for the bike.

Perfect... when this is finished it is going to drive a Flux Capacitor mounted in the former Tach Bezel

 

Sorry 'thatoneguy'... another question. I am looking at the data sheet. Since my signal is a hall effect pulse coming from the Speedometer, would the circuit at the bottom of page 5 be a simpler solution and could I still stack 3 LM3916's?

 

Ahhh, the LM3916 is for VU meters (audio). The LM3915 is a log scale.
The LM3914 is for a linear scale, which is what you want.

National Semiconductors' page for the LM3914:
http://www.national.com/mpf/LM/LM3914.html
Datasheet: http://www.national.com/ds/LM/LM3914.pdf

 

Sorry 'thatoneguy'... another question. I am looking at the data sheet. Since my signal is a hall effect pulse coming from the Speedometer, would the circuit at the bottom of page 5 be a simpler solution and could I still stack 3 LM3916's?

Yes, the page 5 figure would work. It is a matter of getting the calibration. You stated it gives 8k pules/mile to the odometer? Do you need a full electronic dashboard, or just the LED display to highlight the needle for looks?

Sarge had a good catch with the dB/Analog LM3914 dot/bar display, using the 3916, an LED would light up each time your speed doubled, so it could be rated for Mach. Assuming you aren't putting this in a Bugatti, the LM3914 is what we'll use.

If it is to highlight an existing, can you post a photo of the speedometer as it exists, with dimensions/diameter? That way the spacing of 30 LEDs could be decided. On the bike, it will require surface mount LEDs, but I believe 3mm/5mm LEDs will work in your application, if you have 1/2" space behind the spedometer cover to work with.

Roughly, output is 11.1 Hz / mph
+/- 10% accuracy would put the unit within visual size of a 3mm LED with spaces around it, assuming a 2" radius "needle".

Working with 8k pulses/mile, here's a rough chart:
Stopped: 0 Hz
1mph= 2.22 Hz
2mph= 3.33 Hz
3mph = 6.66Hz
4mph = 8.88 Hz
5mph= 11.11 Hz
10mph= 22.22 Hz
15mph = 33.33 Hz
20mph = 44.44 Hz
25mph = 55.55Hz
30mph = 66.66Hz
35mph = 77.77Hz
40mph = 88.88 Hz
45mph = 100 Hz
50mph = 111.11 Hz
55mph = 122.22 Hz
60mph = 133.33 Hz
65mph = 144.44 Hz
70mph = 155.55 Hz
80mph = 166.66 Hz
90mph = 200 Hz
....
...

Mach 1 = 1.511 kHz

 

Yes, the page 5 figure would work. It is a matter of getting the calibration. You stated it gives 8k pules/mile to the odometer? Do you need a full electronic dashboard, or just the LED display to highlight the needle for looks?

Sarge had a good catch with the dB/Analog LM3914 dot/bar display, using the 3916, an LED would light up each time your speed doubled, so it could be rated for Mach. Assuming you aren't putting this in a Bugatti, the LM3914 is what we'll use.

If it is to highlight an existing, can you post a photo of the speedometer as it exists, with dimensions/diameter? That way the spacing of 30 LEDs could be decided. On the bike, it will require surface mount LEDs, but I believe 3mm/5mm LEDs will work in your application, if you have 1/2" space behind the spedometer cover to work with.

Yeah, I have roughly 4" behind the display within the old Tach to make this work (I have gutted the old tach to use as a mouting harness.) What I essentially want are a total of 9 or 12 LEDs (or more) arranged into 3 lines pointing toward the center of "Gauge" (like a mercedes symbol.) I am building a "Flux Capacitor" ala Back to the Future to fill this empty space in my dash. Ideally, they would be off at 0 and fill to the center point and flash at 60 - 70 MPH (I would likely soil myself if my 1988 Jeep reached 88 MPH). I think the "Bar Display with Alarm Flash" in the LM3914 Data sheet (http://www.national.com/ds/LM/LM3914.pdf) would work best for this, however I will need to tie 3 together for it to work.

Thoughts?

 

If you plan on having 3 rows "converge" on each other, then one driver is all that is needed, since all three would be displaying the same thing, sort of "lighting up inwards" in a ring.

I'll have to watch the movie again. I watched it in the theater, and have the DVD around here somewhere. I guess we might as well make it authentic.

 

LOL... I have some translucent acrylic tubing and some small end caps to complete the effect and give it a little glow.

 

If you are any good with graphics, or even if not, can you sketch out the design to guess how many "steps" there should be from outside to center?

also if more than one is wanted on at a time, it gets a bit more complicated, or if a fade effect is wanted if moving in "dot mode". Nearly to the price of a microcontroller, which would make the cost a microcontroller, optoisolator, LEDs, and transistors. Would have option of a digital speed display then as well. Cost: Basically the same.

 

If you are any good with graphics, or even if not, can you sketch out the design to guess how many "steps" there should be from outside to center?

also if more than one is wanted on at a time, it gets a bit more complicated, or if a fade effect is wanted if moving in "dot mode". Nearly to the price of a microcontroller, which would make the cost a microcontroller, optoisolator, LEDs, and transistors. Would have option of a digital speed display then as well. Cost: Basically the same.

I will try to get that too you today, however I have to spend my lunch making a hidden buzzer using a 555 Timer IC for April Fools

 

This is a pretty poor graphic (MS Paint in Win7) but you get the idea.


Ideally, the outermost LEDs in all three lines would light up at something like 5 mph, then the next in each at 15, etc. When max speed is reached they would all flash. I agree that a microcontroller is now probably the best idea, since with the proper coding we could do almost anything.

 

Bump bump bump

 

Dargh, missed the bump!

Ok. Do you have a PicKit 2 programmer?

A 16F628A or similar 18 pin could do this, though it would require driver transistors for the LEDs (2 input and 14 outputs with internal oscillator mode).

1 Input would be to count pulses, 6 outputs for driving the LEDs, and leftovers for... whatever. I'm thinking each "speed" would drive 3 LEDs, one in each line, the next speed would drive the first and second in each ring, etc. When at 88mph, all 5 (15 in ring total) would blink. Or are there 6? I can't see the full size image..

Is there a center LED that would be a different color to flash as well? Enough outputs are available..

 

I do not have a PicKit2, but I have no problem purchasing one for this and/or other projects. the PicKit 2 Starter kit I am looking at here: http://www.microchipdirect.com/productsearch.aspx?Keywords=DV164120 comes with the PIC16F690. Would that work?

There will not be a center LED and there will be 5 LEDs in each line (space issues might require us to go to 4.) If we go with 5 in each, each speed unit could be 13 MPH and then it would flash at 65MPH. This is a 21 yr old jeep. I would soil myself if it ever hit 88 MPH.

If you can help me put together a parts list, I can start ordering right away (before the wife gets back from Vacation.)

 

LOL @ Wife. I know that road!

From Microchip:
http://www.microchipdirect.com/productsearch.aspx?Keywords=DV164120 $50 for PicKit 2 Starter Kit.

Then

For actual use in the car, either:
Part Number: DM164120-1 - PICkit 2 Low Pin Count Demo Board
or
Part Number: DM164120-2 - PICkit 2 44-Pin Demo Board

The first one is what comes with the PicKit 2 starter kit, and also has a spare board with no processor or LEDs. I have something close, but with a 16F628 processor.

The second one is pretty small, 2" x 3 1/2", and has 8 LEDs, a button, and a pot on it, I have one of these. Runs at 3.3V.

Both are $23, up to you for size.


From DigiKey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=399-5440- ND - 0.1uF caps, x10 - $1.04
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=497-3436-5-ND $1.50 - 5V Regulator (For starter board)
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=497-3450-5-ND $1.50 3.3V Regulator (44 pin demo board)
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P819-ND22uF cap 10x - $1.03
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=493-1579-ND - 220uF cap $3 for 10
LED's, I was thinking rectangular turquoise or blue, Search under Optoelectronics LEDs - <75mA, Discrete For the style you'd like.
Blue Oval Surface mount square/rectangular would fit together nicely for more LEDs and a "Line Look".

Radio Shack:
Prototype Board to hold LEDs, Hook up wire, heat shrink, resistors, Pack of general purpose NPN Switching Transistors (2n4401 x 10).

Reason for ordering second demo board: Overall, the car setup alone will be around $35, using a Demo board for the brain, that solves a ton of setup/debug issues straight off. The other demo board is because if you like electronics, you will be addicted to PICs! They can be used over and over for different projects. The first project, I'd suggest a demo board for size / easy programming/testing/install. After that, either build on proto boards or etch PC Boards.

 

This is great, I will order the parts tonight...

 

Oh, and an opto-isolator for the speedometer input pulses.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=TLP351F-ND Logic level push-pull output, DC input.