The other night I was riding my Nordictrack exercise bike and all of a sudden the display quit and the tension on the peddles went slack. The wife has been on me for quite some time to start exercising as I sit behind the computer the major part of the day.

So I decided to take the thing apart and see If I could trouble-shoot what was causing the control and display not to function. I will get into showing you the tear down shots later.

Right off of the bat I thought, cool if the controller is shot I could replace it with a micro-controller solution.

This would be a cool project.

But then reality set in and I realized that this project would take some time and I am currently working on some other micro-controller projects. So back to tearing the thing down and see if I could fix the darn thing.

The display has two sets of connectors coming out of it. I had no clue to what they were connected to. So I decided I had to tear the plastic off the bike and take a look at how the bike was wired.

Grabbed the multimeter and some tools. Stripped the bike down to the frame and started taking a peek how this bike works.

Lets take a look at the key sections of the bike.

Step 1: AC Adapter

We will start at the front of the bike. Notice the ac adapter, 12 volts, 1 amp DC adapter.

Step 2: The Pedal Assembly

A bit further back, The pedal assembly, Notice the Hall Effect sensor and the magnet mounted to the pedal assembly.

The Hall Effect sensor is used to count the number of wheel rotations and calculate things like speed and distance traveled. Along with the hall effect sensor and the weighted wheel potentiometer, calories burned can be calculated.

Step 3: Rear Weighted Wheel

At the rear is the business end of the exercise bike, there is a weighted wheel with a tension adjuster and a motor.

In a minute we will look at how the motor and wheel works.

Step 4: Motor Assembly

Lets take a closer look at the motor assembly.

On the motor we have a lever and a gear wheel no unlike a RC servo motor. So this motor my be controlled like an RC servo motor? maybe, lets troubleshoot some more.

So we flip the motor over and notice how the motor is wired:

The motor has two wires connected, a yellow wire and a blue wire, no this motor is not an RC servo, it is just a DC motor.

Also on the motor control casing there is a label.
On the label it indicates “6V tension motor P/N 241949″

I did some web searching and found that many exercise bike use this same motor.

But I could not find any specifications on the motor. Just a few posts where other people have had some issues and one article on a vague description on how to test the motor by applying some current to the motor to see if the motor gear turned or not.

I flipped the motor to the other side and had a look:

Interesting, There is a 5000 ohm potentiometer on attached to the gear of the motor.

This would mean that when the motor is adjusted to increase the tension of the skid closer to the motor the resistance would increase and likewise when the motor reduced the tension against the wheel the resistance would decrease.

At least that is what I guessed. Lets do some testing.

So I installed the motor back into the exercise bike and put some batteries together for some testing. I applied some voltage to the yellow and blue wires and sure enough the motor started to turn to move the skid closer to the wheel. Just like a servo though there is a stop and you have to be careful not to keep the motor running against the stop.

So then the question is if I reversed the wiring on the motor would the motor reverse direction and turn pull the skip away from the wheel.

I tried it and sure enough the motor changed direction and moved the skid away from the wheel.

I then attached my ohm meter to two of the terminals of the potentiometer and ran the motor forward and backward and the ohm meter read from 0 – 477 K ohms.

The potentiometer readings along with the hall effect sensor are used to calculate calories burned, speed and distance traveled.

I traced the wires back from all connections to the 10 pin wire connector and found out which wires applied power to the display and controller. I also noted where all of the wires from the potentiometer and halls effects sensor came into the wire harness.

Step 5: The Display/Controller

It is time to take a look at the controller/display.

I removed the connectors and display unit from the exercise bike and took it to my work bench.

I opened up the display/control unit and took a peek inside, not a good sign, other than a few capacitors there were no discrete parts, just a bunch of chips.

So I disconnected the keypad and speakers and the iphone dock connectors and applied power to the unit. Instant current overload on the adjustable power supply.

I tried to check a few connections but not much else could be tested. It appears to be a chip issue. There were no burn marks on the pcb traces.

So it looked like the controller was fried.I looked on line and a new controller was over $300.00. No freaking way was I going to pay that much for a replacement controller.

So I did some thinking and came up with a quick and dirty way to get the exercise bike working for around $15.00. Really all I needed was a way to increase and decrease the wheel tension on the exercise bike. I really do not need the fancy data that comes off the bike for the time being.

I could get the bike working and then when I had some time I could come up with a replacement controller using an inexpensive micro-controller solution with a LCD display.

Step 6: The Fix

Did a bit of web searching and drew up a wiring diagram, after a quick trip to radio shack I started to put together a workable solution.

Here is the wiring diagram I came up with:

I picked up a DPDT switch, a DC adapter voltage connector and a momentary push button and a project case that I had laying around on my desk and some wiring.

After wiring up the new controller box I mounted the box to the exercise bike and connected the yellow and blue wires to the new control box:

Notice I connected the output leads to the wire connector using some female jumper connectors. That way when I come up with a micro-controller solution it will be an easy fix to use the existing wire connector.
If you decide to wire up one of you own, you may have to swap the yellow and blue wires in order to have the DPDT switch increase the tension when the switch is pressed in the forward position and pressed rearward to decrease the tension.

There you have it, a working quick and dirty exercise controller. Now I can keep my wife off of my back and get back to my other micro-controller projects.

Enjoy