Here's the unmodified unit. Note the 5-winged adjustment knob.

There are models that have a remote tension lever that attaches the the handlebar, but, I don’t have one of those. Thus was born the idea of using a motor controlled by an Arduino board to turn the knob by pushing buttons mounted on the handlebars. The real trick though was to hook up a motor to the knob. I wanted to avoid modifying the unit, and that included not wanting to drill mounting holes, or use glue on the knob. I tried using Vex robotic parts at first, this worked well enough to prove that the motor was powerful enough to turn the knob, but it was a wobbly contraption, not suitable for more than a proof-of-concept. I searched around for various things at the hardware store. Among them were hex nuts that matched the thread of the adjustment screw. I thought maybe I could use these to create a knob that could be easier to work with than the knob the came with the Kinetic trainer.

Notches in the PVC fit over the knob nicely. The back of the PVC adaptor has enough flat surface to screw the motor coupling plate in place.

The item that  offered the most promise was a PVC adaptor. The part is intended to match a 1 3/4″ pipe to a 1/2″ pipe. What interested me is that the thought that the large end could be notched to fit over the knob, and that the small end had flat surfaces that might be sufficient to drill holes for the motor mounting plate. A Dremel tool and file were all I needed to notch the PVC adaptor so that it fit snugly over the knob. As I had hoped, there was enough flat surface to mount the motor securely. One thing I had to do, that I hadn’t planned was to drill a hole through the side to allow access to the set screw on the motor shaft collar that is on the inside of the tube. With a couple of pieces of flexible metal strap and twine I got the motor unit and PVC adaptor to press against the knob with sufficient pressure. Yes, I said twine. This is still a prototype after all. Imagine if you will . . .yadda,yadda, yadda.

The motor is driven by an Arduino board. Cat5 cable runs to the handlebars for the control buttons.

The electronics were the easy part. Arduino has sever digital ports that can drive a PWM controlled-motor. The Vex motor units I have are free running servos that can be driven very easily with the Arduino by using the Servo module. By using a value of approximately 90 in the Servo::write() method, the motor will be stationary. A value of 0-89 will cause the motor to turn in one direction. A value between 91 and 128 will cause it to turn in the opposite direction. Wiring is pretty standard. The black wire from the motor goes to ground. The red wire goes to the motor supply voltage. The white wire goes to the signal port, in this case the digital port 9 on my Arduino board. Controlling the motor is done with two button switches attached to digital ports 5 and 7. Each port is tied to ground with a 10K resistor. Each switch then is tied to the Arduino 5V supply. When pressed, the digital port is pulled up to make the digitalRead(portNumber) method return TRUE.

The left button decreases the tension. The right button increases it.

The Arduino code is very simple. The main loop looks for one of 3 conditions–left button pressed, right button pressed, or no buttons pressed. If the left button is pressed, then the motor is turned in a direction to decrease the tension (allow the wheel to spin more freely). If the right button is pressed, the motor, spins the opposite direction, increasing tension (making it harder to pedal). If neither button is pushed, then the motor is held stationary.

There are several things that I would change about the code. First, there is no need to continuing writing the motor direction control during the whole button push. It can be done once, when the button is first pressed. The code runs fine as it is, but it is wasting time with continuous writes that do nothing useful. There should also be some sort of debouncing for each switch. Finally, it would be useful to have have some safety limits built in to prevent excessive tightening and loosening. This would likely require a third switch to put put the unit into a calibration mode. Once the calibration mode is turned off, then the unite would only allow a set number of turns in either direction.

Here is the code.

Here is what the matrix looks like. The anodes of  LEDs were wired in rows and the cathodes in columns. Thus, to turn on an LED, the proper row and column had to be set to high and low voltages. The next task was to hook this up to an Arduino board and create messages by flashing one character at a time. I drew out the characters on paper and then created binary numbers where the digit ’1′ represented an illuminated LED and ’0′ one that was turned off. A full character would look something like this.

‘B00100′

‘B01010′

‘B11111′

‘B10001′

‘B10001′

In this case, this is the letter ‘A.’

My wife and I are interested in making safety clothing for night bicycle riding and thought this might be useful. We ordered a five foot section of 3mm wide cable from here. Once I had the cable in hand, I attached a bright red LED to each end with shrink tubing.

End connections

A quick test shows that two LEDs provides a fairly even glow along the entire length of the tube. Each LED was rated to deliver 18,000 millicandelas of light.

Two LEDs powered up

This looks like it could be used on a bicycle helmet to provide a flashing illumination. More to come as we experiment.

Original bottom view

I had been experimenting with a simple circuit called a Joule Thief.  This circuit boosts a DC voltage to a higher voltage.  It’s is easy to make with easy to obtain parts.  The Web is full of plans for these devices.  The advantage for this project, is that such a circuit can drive a bright white LED from a single 1.5 Volt battery.  I figured that I could easily fit the circuitry and a single AAA battery into the battery compartment of the book light.  This would save batteries and provide a more even light across the page of a book.

Joule Thief

I replaced the incandescent bulb with a bright white LED that I encased in aquarium sealant inside of a short length of clear plastic tubing.  This helped to diffuse the light along the approximately two inches of tubing that the LED was attached to.  Here’s the final assembly and it’s use.

Ready to use

Modified lamp in use

wolfstone.halloweenhost.com

Breadboarding this was fairly easy and took just a few minutes.  I keep a lot of components around with breadboard wire already soldered, so that makes prototyping a lot faster.

Before I attached the motor, I verified that the circuit was performing as needed.  With the oscilloscope set to show 5 ms per division I could measure the minimum pulse width of 1.15 ms and a maximum width of 2.75 ms.

This seemed good enough to try, so I plugged in the motor.  The black wire is ground, the red (or orange) wire is positive, and the white wire is the signal (pin 3 on the 555).    I had nearly the full 100 degree rotation in the motor as I turned to potentiometer shaft back and forth from minimum to maximum.

Just for fun, I substituted a flex sensor for the potentiometer.  Not quite the same amount of rotation, but, I didn’t bother changing any other component values.

Servo Motor with Flex Sensor from Patrick Lewis on Vimeo.

Pennies with hookup wire soldered to them. Foam is packing from a power MOSFET.

The next step was cut some plexiglass sheets and then use some double stick tape to attach a penny to each sheet. Then I bolted the two sheets together, presssing the foam in between. Here’s the assembled unit.

Platform assembled, and hooked up to ohmmeter to test base resistance.

This setup didn’t work out so well as a scale. Heavier objects placed on the scale took a long time to reach a stable value. I figure that the foam continued to compress slightly for two minutes or more. Also, it took a similar amout of time for the scale to return to it’s base value.

This arrangement seems to work best not as a scale, but as a pressure pad, particularly as a pressure-relief pad. For example, it might work well to sense when an object, such as a book, is lifted. Don’t anyone dare try to steal my “Programming Python book!”

Now I know why the power sucking pig of an electomagnet I made from hookup wire and a nail is so hard to drive with a power MOSFET.

Also, shows why sometimes you are better off just buying controller chips that do the job you want than to try to roll the circuitry yourself with discreet components.

I dug out an old robot arm kit that I had built a long time ago. It was originally operated by push buttons for each motor with a slide switch to reverse the polarity of the current and thus the direction of the motor.

With an Arduino module, a couple of H-bridge chips, and a bit of surfing for ideas, I managed to automate it to drop a washer in a small container. The main idea comes from this page page, which describes how to hook up and control one motor. Learning to control two motors is largely inspired by this diagram.

Here it is in action. I had bigger plans for what it would do, but, it is after all, just a cheap kit with plastic parts. The jaws barely have enough grip to hold a small washer. It is a good proof of concept for controlling multiple motors with a single arduino board.

Wiring code for robot arm