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[on:]

Hi all,

I'm considering my first proper Arduino project. I've got a fairly cheap exercise bike. The bike is great, but the LCD readout is hopeless, and there's no way to connect it to a PC or anything. I'd like to change that.

The interface between the bike and the display unit is very simple - it looks like a standard 3.5mm audio jack, and I'm *hoping* that the signal is similarly simple. The problem is I'm not really sure if there's a safe way to figure out the signal format without blowing up my board. Can anyone recommend a circuit layout that'd let me figure out the format without causing damage to my board. All I really want to start with is to safely connect the 3.5mm jack to an analogue input and monitor the values. Is that even possible without figuring out the voltage/current with an oscilloscope first?

I'm comfortable enough with the software side, I'm just not sure where to start with the electronics.

Any help much appreciated,
Rob.

[Reply #1 on:]

Do you have access to a volt meter, or even better an oscilloscope ?

It would be a good idea to measure what ever is on that jack before doing anything with it.

Measureing or "scoping" the ignal could also give you an idea about what the signal is (probably a series of pulses).

[Reply #2 on:]

Hi all,

I'm considering my first proper Arduino project. I've got a fairly cheap exercise bike. The bike is great, but the LCD readout is hopeless, and there's no way to connect it to a PC or anything. I'd like to change that.

The interface between the bike and the display unit is very simple - it looks like a standard 3.5mm audio jack, and I'm *hoping* that the signal is similarly simple. The problem is I'm not really sure if there's a safe way to figure out the signal format without blowing up my board. Can anyone recommend a circuit layout that'd let me figure out the format without causing damage to my board. All I really want to start with is to safely connect the 3.5mm jack to an analogue input and monitor the values. Is that even possible without figuring out the voltage/current with an oscilloscope first?

I'm comfortable enough with the software side, I'm just not sure where to start with the electronics.

Any help much appreciated,
Rob.

How many different segments are there on the 3.5mm jack. (most have 2-3 on them)
Odds are theres an encoder on the wheel to tell the RPM of it.

[Reply #3 on:]

Cheers for the responses. The jack only has two segments.

Checking with a voltmeter, it looks like a pulsing signal (pulsing once per revolution) up to a volt or so (the voltage actually seems to vary by velocity - I'm hoping it's something simple like velocity*resistance, but I'll figure that out later).

So (showing my utter incompetence at electronics) does that mean it's low enough to wire the -ve end of the jack to the GND and the +ve into an analogue input, or do I need to worry how much current that's going to shove through. Is there a safer way to go about it?

[Reply #4 on:]

Varying voltage is possibly an artifact of your voltmeter being slow to react. Have you tried putting the wheel in the position where the (presumed) hall sensor is providing a reading and measuring it when it is stopped?

[Reply #5 on:]

it looks like a standard 3.5mm audio jack

If it comes from the rotating part of the bike, it may be just connected to a hall effect sensor. Rotate the wheel slowly and see if you get distinct blips on your meter.