# Suggestion for a lack of light warning unit when in motion

I would like to build a small device that warns me, with sound and or a 'dash' lamp, that my headlight is off if the motorbike is moving. My challenge is it is under warranty, so I cannot in any way modify or attach to existing wiring. The unit must strictly only connect to the bike by something like silicone glue or Velcro.

I first though of an accelerometer in combination with an Arduino or something, but now I've wondering if a simply unit could be made with some kind of pendant switch, as I only need to detect some acceleration, not the magnitude of it.

The unit would be smallish, with a light sensor on one end, and a bright LED array on the front, to provide an iota of emergency visibility if the rider doesn't hear or see the warning for some reason.

The main gist of my question is, once the light detector and alarm is built, how do I enable it only when in motion?

BTW, the main use of this is for when a motorcyclist forgets to switch on his headlight during the day. It's quite easy to notice that it's off at night.

• "Bike" as in motorcycle? – Wossname Jan 29 '16 at 11:42

Use a dynamo to power your circuit. This is how old bike lights used to work before batteries became more popular. This way motion detection is passive and all you need to do is have a buzzer sound when a light sensor reports darkness.

You can still buy small clip-on bike dynamos cheaply and you can just modify one of those into a single device that has the buzzer and light sensor built in.

These devices simply have a shaft with a friction wheel on one end that presses against the tyre and spins powering a small generator. Simple and effective.

• Did the OP mean motorbike or pushbike? – Roger Rowland Jan 29 '16 at 10:53
• @RogerRowland, It's hard to know isn't it? You'd have to ask the OP. Sounded like a bicycle question to me. Motorcyclists are less likely to forget their lights in my experience. – Wossname Jan 29 '16 at 11:37
• Agreed, but he's talking about "existing wiring", "dash lamp", and "headlight" rather than "front lamp", which makes me wonder. – Roger Rowland Jan 29 '16 at 11:39
• Hehe, I have a "headlight" on my bicycle helmet. The OP used dash light in quotes suggesting it's an odd term to use which makes sense in bicycle terms. English is a funny language sometimes. – Wossname Jan 29 '16 at 11:44
• @RogerRowland A motorbike. – ProfK Jan 29 '16 at 12:17
• Use a bike speedometer magnet and reed switch to detect motion.
• Feed the signal into some logic to detect pulses and light LED if headlamp photosensor is not detecting light. You need to shade the photosensor from daylight (if you want lights on during the day).

The whole idea seems a bit complicated. I have pondered similar questions as I can't easily see the tail light on my bike. One idea I had was to run a fibre-optic strand from each light to a 'console' on the handlebars so I could tell if each lamp is on.

• Not a bad idea, even simpler if I neglect to expand on just the headlight, but I would have to use the output of the fibre to trigger an LED; it wouldn't be visible in the day, i.e. the important time where motorcyclists forget to put their lights on. – ProfK Jan 29 '16 at 15:57

simulate this circuit – Schematic created using CircuitLab

Figure 1. Spoke motion detector with LDR sensor for headlight.

The main problem will be building a thru-beam light sensor. I suspect you'll need some lenses or purchase a ready-made unit, but here goes.

• R1 and D1 are the light source and positioned on one side of the wheel.
• Q1 and R2 are the light detector and positioned on the other side of the wheel.
• A few CMOS inverters (use all six on a chip if the others are spare) drive the charge pump C1, D2, D3 and C2.
• When the left side of C1 is driven low, the right side will follow. D2 prevents it going negative. When the left side is driven high the right side will follow and charge will be transferred via D3 to C2.
• When voltage builds up on C2 Q2 will turn on lighting the LED.
• If the headlamp is switched on the LDR will shunt the base voltage for Q2 and the LED will be turned off.

This is an 'out-of-my-head' circuit. You would need to play around with the LDR / R4 combination to get the right response in daylight.

Frequency calculations

These may be useful to somebody.

I don't know much about motorbikes but lets say we have a 600 mm diameter wheel and five cast spokes. $Circ = \pi \cdot d = \pi \cdot 0.6 = 1.8 m$ approx. per revolution. 108 kph = 30 m/s and would rotate our wheel $\frac {30}{1.8} = 16.6 revs/s$. With 5 spokes that would be 83 Hz signal if we detected each spoke.

• Thanks, great circuit, but I may adapt the right side. My electronics expertise (I once could use transistor parameters to find the correct one) is now down to early school basics. It's with projects like these I hope to reawaken it. – ProfK Jan 30 '16 at 3:03

An interesting option is what is used for bike velocity meters : a small magnet attached to the bike while (on a wheel wire usually) and a hall effect sensor attached to the fork. Then each time the wheel completes a turn, the magnet passes in front of the sensor and is registered as a pulse from the sensor.

Use a motion sensing trembler switch and a light dependant resistor (or more elaborate sensor) drive a buzzer, power from a PP3 9V transistor battery for a long time if you drive with the light ON and the buzzer only sounds occasionally when you get on the bike.

Take the LDR and stick it to the front of the headlamp facing in with clear silicone or hotmelt glue and use self adhesive hook and loop fastener to mount the rest of the birs nearby in a waterproof box.

The LDR will goes to high resistance when the lights are on and if the vehicle is moved it will buzz only if the LDR is dark. It will also works as a ULTRA cheap anti theft alarm.

simulate this circuit – Schematic created using CircuitLab