Be forewarned about known hazards while you’re driving

How often have you found yourself surprised by the presence of a speed camera while driving, your attention distracted while you doublecheck your speed? Or come across a sharp bend in the road and had to break sharply? Too often in the author's case, many times at the same spot. Wouldn't it be great if you could have a simple device that would gently warn you of these oncoming “black spots”?

Although speed cameras are controversial they are (in the main) located where speed control is important, so having a device that can remind you to take extra care has its merits. The purpose of this project is to produce a device that can advise you of places that require attention to speed, not to help you avoid prosecution for speeding!

This design monitors its own precise location using an embedded GPS (Global Positioning System) receiver, and alerts you to oncoming pre-recorded blackspots. As you drive past a speed camera or blackspot to which you want to be alerted on a future occasion, you press a Record switch on the unit. This stores the current location into the device's memory, a nonvolatile EEPROM (electrically erasable read only memory).

The EEPROM can store up to 1000 locations, and once every second the PIC16F873 microcontroller scans all of the stored locations, comparing them to the current position. When it has found the closest blackspot it displays your distance from it on an l.e.d. bargraph. When you get very close, a low level beep is emitted. A second button is used to cancel the beep, and it also functions as a delete key to remove unwanted locations from the EEPROM.

This all sounds like a nice and straight forward design but it conceals some complex maths, an interesting limitation of computers in general and some devious mathematical simplifications. Normal fare for an embedded micro project!