Misterbenn
Active Member
Hey there!
I want to add a bit of extra security to my bicycle, so i'm going to build a bike alarm.
Now its easy enough to get a wire and a piezo siren (110db) wired up so that if your lock gets cut the alarm goes off. But thats not INTERESTING! I want my alarm to go off as soon as the bike or lock is moved.
Clearly i need to detect movement and the best way is to use an accelerometer. This will be a 3 axis accellerometer consisting of 3 piezoelectric sounders, clamped at one end and with a weight at the other (this need carful consideration of the resonant frequency). The individual Piezo outputs will be fed into a charge amplifier with adjustable gain and the output stage conected to a darlington array.
Any one of the three accelerometers will triger a 10s siren, while a cutting of the lock cable or tampering with the device will result in a constant siren.
The alarms locking cable wont provide a strong physical lock so i'll always have my usual bike lock as well. The cable is of the three core armored type, its also transparent so it acctualy looks like a normal locking cable rather than a peice of electrical wire.
A tamper sensor will be in the form of a light dependant diode in the casing. The deivce will be turned on with a pushbutton, and turned off with a key switch.
Power consumption will be a real issue as i dont want to recharge this every other week!
Anyway thats the project, i'm sure i'll need some advice soon so i'll keep you all posted.
I want to add a bit of extra security to my bicycle, so i'm going to build a bike alarm.
Now its easy enough to get a wire and a piezo siren (110db) wired up so that if your lock gets cut the alarm goes off. But thats not INTERESTING! I want my alarm to go off as soon as the bike or lock is moved.
Clearly i need to detect movement and the best way is to use an accelerometer. This will be a 3 axis accellerometer consisting of 3 piezoelectric sounders, clamped at one end and with a weight at the other (this need carful consideration of the resonant frequency). The individual Piezo outputs will be fed into a charge amplifier with adjustable gain and the output stage conected to a darlington array.
Any one of the three accelerometers will triger a 10s siren, while a cutting of the lock cable or tampering with the device will result in a constant siren.
The alarms locking cable wont provide a strong physical lock so i'll always have my usual bike lock as well. The cable is of the three core armored type, its also transparent so it acctualy looks like a normal locking cable rather than a peice of electrical wire.
A tamper sensor will be in the form of a light dependant diode in the casing. The deivce will be turned on with a pushbutton, and turned off with a key switch.
Power consumption will be a real issue as i dont want to recharge this every other week!
Anyway thats the project, i'm sure i'll need some advice soon so i'll keep you all posted.