Fitness bike activated computer

A friend told me about a project where kids can only use the computer when they are pedalling the connected fitness bike.

How to do it: Attach a dynamo to the bike, connect it to Arduino which sends signals to computer. On the computer a program checks if the bike is active and if not, turns off display or locks the computer.

For tablets we could write an app that communicates with the RaspberryPi on the bike. We could use the same wireless design for PC.

Watermelon ripeness detector

Can be made into a smartphone app.

Correlation between sound decay rate or fundamental frequency/amplitude and ripeness.

Melon Meter

https://www.youtube.com/watch?v=LxC67dnyVGU

ppt: http://www.me.udel.edu/meeg447/98/serffiles/fall4-design-reviews/dr-ppt/dr-02.ppt

http://www.researchgate.net/publication/257798409_An_intelligent_procedure_for_watermelon_ripeness_detection_based_on_vibration_signals

Equipment:

1. Microphone
2. FFT and filtering on the Arduino
3. Ripe and unripe watermelons

increase fan rpm with temperature

Add delay to window alarm

Can I do it with analog electronics, e.g. with a capacitor? How do I discharge the capacitor? Does it discharge "slowly" by itself or do I need a resistor/LED? I probably will need a transistor too. Capacitor will be used to control the current flow via the transistor. When capacitor is fully charged, it will let current flow through the transistor which in turn activates the alarm circuit.

If I want a 10 second delay, I can achieve it with a resistance of 100K and capacitor of 100uF [see RC time constant]: tau = 100e3 * 100e-6 = 10 seconds.

https://www.youtube.com/watch?v=GeveeSTyvGs

• Capacitor: 470mF, 100mF
• Resistance: 47K, 22K
• Diode: 1N4001, 
• Transistor: 2N???

https://www.youtube.com/watch?v=LQji9_O9-aI

http://www.the12volt.com/installbay/forum_posts.asp?tid=91691

https://answers.yahoo.com/question/index?qid=20100910203520AAoZUtq

https://en.wikipedia.org/wiki/RC_circuit

Electronics Questions

• How does a capacitor between the terminals of a DC motor act as a filter? How are the transients originating from sparks dissipated/absorbed? See also Why are capacitors capable of suppressing electrical noise in DC motors, RC Circuit, Decoupling capacitor, Bypass Capacitors, Capacitor application examples.
• When a battery is your power source, what is ground?
• Contact bounce in switches/buttons.
• Servo motor buzz/jitter/chatter

Elektronics drawing software

Free tools [reference]:

• Fritzing
• InkScape

Magic Mirror with Raspberry Pi

http://michaelteeuw.nl/post/84026273526/and-there-it-is-the-end-result-of-the-magic