I wasn’t sure whether it was worth writing this project up, as there are several descriptions already on the internet of people tapping into the Vespa alarm header in order to make a turn signal beeper. However the ones I’ve seen are all very simple direct connections of a piezo buzzer to the turn signal wires (via diodes). This project is a little more sophisticated in that it uses my old friend, the PICAXE microcontroller (see my “Pimp my Rocket” post for another PICAXE project). It’s still quite a simple circuit, but it has allowed me to program how and when I want the buzzer to sound, and has allowed me to audibly distinguish between the left and right turn signals. I’m not going into great detail here, but I thought a quick write up might give others some ideas for their own projects.
The problem to be solved is a common one for many motorcyclists, namely sometimes forgetting to turn the turn-signals off. This of course sends the wrong signal to other motorists and is potentially dangerous, or at least annoying. It also makes you feel like a chump if you’re the offender. My bike, a Vespa GTS300ie Super, has no audible turn signal warning. It has single dash light for the turn signals – but this is of limited use if you forget because, well, you’ve forgotten and you’re looking at the road ahead, not checking the dash. The last time I forgot to turn off my turn signal I thought, right, I’m going to fix this. I remembered the piezo buzzer that I had removed from the annoying kettle (see my post on de-beeping a Kitchenaid kettle) and thought that it would be suitably ironic to make good use of a device that previously had such a useless function. Unfortunately when I tested it, it wasn’t loud enough to be heard on the road! I had to go out and buy another piezo which was specified as 12V, 15mA (max.), 3.3kHz, 90dB (distance not specified, but loud enough to be easily heard through helmet, engine noise and moderate wind noise).
The circuit drawings below don’t show diodes on the turn signal inputs. They should not be necessary since the left and right turn signal wires are not being connected to each other (which without diodes would result in both signals flashing together). You might notice, however, that my circuit board below has diodes. When I first built it on a breadboard, I had the turn signals connected as a single input and thus needed diodes. When I decided to separate them for greater functionality I figured it wouldn’t hurt to leave the diodes in.
The parts of the circuit shown above are the power supply for the PICAXE chip, which takes inputs from the +12V and ground pins of the alarm plug, the voltage dividers (top right) which take the 12V from the turn signals down to about 4.3V for the PICAXE inputs, and the piezo switching transistor (top left) which allows the 12V piezo to be driven by the PICAXE.
In figure 3 above, the blue and white wires go to the right and left turn signal pins of the header plug. The red and black wires go to the switched +12V and ground pins of the header plug. The two header pins on the circuit board connect to the piezo buzzer. Note that there is no PICAXE serial programming circuitry, which is why the 08M2 PICAXE chip is in an 8-pin I.C. socket – so that it can be removed for re-programming on a breadboard. You might also notice that PICAXE pin 4 is connected to an unused pad. This was for possible future use such as connection to a brake signal.
The smallest box I had easy access to was about twice as big as necessary, but it still fitted in the space available (see below).
The alarm header plug is located behind the left “knee cover”. I have a Stebel air horn mounted in this space, but still found room for my circuit box. In fact it was quite good, because the box is quite snug in there and doesn’t move or vibrate. I didn’t have the male counterpart to the alarm plug, so I had to make do with diode lead off-cuts soldered to the wires. I found that these (which have a diameter of 0.7mm) fitted snugly into the connector. It’s not ideal, but will do until I can find a proper plug.
The way I have programmed it to work (and I won’t include my inelegant code here) was to have a short beep every three seconds while the left turn signal is on, and a short double-beep every three seconds when the right turn signal in on. Thus I can tell not only that the flasher is on, but also that the correct flasher is on. These beeps continue for about 45 seconds (15 x 3 second loops), after which the program switches to a more intrusive “mimic” mode where it continuously looks at the turn signal inputs and switches the buzzer on or off to match (equivalent to a simple direct piezo connection circuit). The short “peeps” every three seconds are enough to remind me, but not so obnoxious that they are annoying. And the 45 seconds is long enough to get through waits at traffic lights. It all works really well, and is already an indispensable addition to the bike.