Pulses to proportional voltage

Oct 28, 2008 10 Replies
A

I want to add a speedometer to my gokart. I expect to mount a magnet to the wheel or axle. I have an existing 15V meter used as my battery monitor, I want to use this and just switch between speedometer and battery monitor. I want a circuit to convert the wheel pulse to a proportional voltage. The kart would move three feet per revolution. I'll design it as a 45 mph F.S. speedometer.



1 mile = 5280 ft and 3 ft per wheel revolution so 1760 revolutions per mile.
30 mph will produce 880 pulses per minute or 14.67 hz. So, 14.67 hz should produce a 10 volt output to the meter. Well this seems like a pretty low frequency to work with, 10 mph would be a frequency of less than 5 hz. Can it be done, or do I need more pulses? I've never worked with the simple PICs, maybe it's time? Ok there's the info, what do you suggest? Thanks, Mike


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A

Sorry, about the double post, it wouldn't leave my outbox and then when it did, I sent two. Oh, ditto about the top posting. ;-) Mike

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J

Doppler ?:-)

Seriously... a micro can simply measure period and convert to MPH. However the slow update rate of every 200ms at slow speeds might be disconcerting.

Why not use more magnets (or pole pieces)?

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It\'s what you learn, after you know it all, that counts.
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J

'Nother thought: Don't you have sprocket drive? Count the "poinkies" on the sprocket ;-)

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | "The American Republic will endure until the day Congress discovers that it can bribe the public with the public\'s money." - Alexis de Tocqueville
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C

mile.

Bicycle speedometers do this already - using a reed switch that closes

1/rev. Generally these are programmable with the tire diameter, though yours may be smaller than allowed. Cheap, nicely packaged solution if it works

- worth a look... You didn't say whether you needed a visual indicator or wether you were data logging...

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A

I want to display the speed on my 15v anolog meter. Mike

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L

something like this? ;)

formatting link

-Lasse

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A

Thanks, for the URL. $9.99 amazing! Mike

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J

I like the "ergonomic" bicycle saddle...

formatting link

Engineered "fart clearance" ;-)

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | "The American Republic will endure until the day Congress discovers that it can bribe the public with the public\'s money." - Alexis de Tocqueville
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A

I sent an email asking about the minimum tire size that the SW654 would calibrate with. If it won't work with an 11 inch tire, maybe a divide by two between the pickup and the speedometer. Mike

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A

I called the company that makes the speedometer and I got a diffinitive answer. ;-} They don't know, "it's only been tested on bigger bikes", nothing with an

11" tire. I'll get one on order and do testing for them! Mike
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