Speed sensor

[Deano11]

Hi, I'm a bit new to all this,

I have a AXE110P data logger with the LCD and clock options.

I am looking for a way to measure speed on a bicycle wheel. I looked at the count command but this ties up the PIC while it counts. I need it to be doing other things.

Is there an easy (?) way to sense speed externaly and present that as an analoge voltage so it can be sampled and scaled every second?

Cheers

Deano

 

[eclectic]

Deano.

As background, I suggest you make a start ,
by using Advanced search, using the terms

bike speed*

There's been a lot of ideas on the forum.

e

 

[Andrew Cowan]

Hall effect sensor (or reed switch) on the wheel?

This could count the rpms.

 

[Dippy]

Andrew, it's all been done and some excellent detail is available if you do as Eclectic says... search.

There's no point re-inventing the wheel haha

 

[Mycroft2152]

Andrew, it's all been done and some excellent detail is available if you do as Eclectic says... search.

There's no point re-inventing the wheel haha

Dippy,

You stole my line!

I thought plagarism was frowned upon.

But if you are going to steal, then steal from a reliable source.

:0

Myc

 

[Dippy]

So sorry Myc.

It was a wheel shame you didn't post first.
So I guess I spoke on your behalf.
I get quite tired of puns.
It's a riminder not to pinch other peoples lines.
Jokes of this caliper should be voided, so I'd better brake off now.

 

[eclectic]

Puncturing the jollity,

A possible scenario.

1. Use a fork-mounted reed sensor from a cheap bike-speedo. (Save the display)
2. Use four or eight equally spaced magnets on the spokes.
3. "Read" the input using a separate 08M
4. The 08M "sends" an analogue voltage using PWMout. (With smoothing).

5. The Master Picaxe can read the voltage say once a second.

 

[hippy]

COUNT ties up the PICAXE but may be okay when moving at speed as you only need a short sampling period to count the revolutions. When moving more slowly you can use PULSIN which determines how long it takes the wheel 'trigger' to pass the sensor which is quite a long time when slow, very short when fast. You can switch between the two ways of measuring speed depending upon how fast you are going from the last reading to choose the most appropriate one.

These tricks and much more related to bike speed are discussed in previous forum posts so a Search is the best place to start.

 

[Mycroft2152]

Deano11,

If you add a second sensor on the wheel, at some propoprtion of the circumference, you can then calculate the rpm and not tie up the PICAXE.
Myc

 

[Deano11]

3. "Read" the input using a separate 08M
4. The 08M "sends" an analogue voltage using PWMout. (With smoothing).

5. The Master Picaxe can read the voltage say once a second.

That's the idea I was looking for! I don't want to tie up the data logger counting. I guess I could also run a cable from the 08M to a 5 volt analogue volt meter to get an easy visual readout? This would have the double bonus that it would still give an indication of speed even if the data logger was not logging.
Thanks folks.
Deano

 

[eclectic]

"analogue meter" Deano.

Shame on you!

Use a 20M with a line of LED's.
Or go flash and use a 14M and see how many you can multiplex.
e.

 

[inglewoodpete]

An analogue meter has its advantages when used with a PICAXE PWM. Although its suitability on a bicycle will depend on how often you plan to crash or ride on rough roads. Also, you need to be able to be able to keep moisture out (unless you live in Adelaide, where it doesn't rain any more )

I have used a couple of different 'scrounged' analogue meters with PICAXEs, taken from old tape players, but not a bike. Note that analogue meters measure current, not voltage, so you need to uses a series resistor to reduce the current to suit the meter. Meters with an FSD of 50 to 500uA are ideal.