Odd Software for Odd Jobs

Bike Sonar, part 5

I've been working on a "Mark 2" version of my Bike Sonar project.

I'm trying a MaxBotix ultrasonic sensor:

2016-02-11 17.01.46-1

I've also thought of using a wireless beeper. My original idea was to have it mounted on my helmet, but when I was fiddling around, I added an LED to the receiver circuit. Then I thought, what about mounting it on my handlebars?

After some tinkering, I managed to get the breadboard prototype working. You can see the transmitter (with MaxBotix ultrasonic sensor) on the right (with a yellow wire being used as an antenna):

2016-02-22 08.33.39

It's a pretty simple circuit - the 433MHz receiver will take a max of 5.5V so I'm using a diode to drop the (nominal) 6V from the 4xAA to less than that. This feeds the Vcc on the Rx board. I've got a 1µF electrolytic capacitor across the Vcc and DATA pins on the receiver - without it, the signal was VERY noisy (Instagram video). The DATA pin is connected to the base of an NPN transistor via a 100KΩ resistor. The emitter of the transistor is connect to ground and the collector is connected to the negative pin of a piezo transducer. The positive pin is then connected to the positive side of the battery pack.

Now this is my very-first "own designed" circuit, simple as it may be. I still haven't figured this out yet, but I had to add an LED between the transistor's collector and ground for the piezo buzzer to sound (and the LED lights at the same time).

When I replaced the transducer with a different type, I had to remove the LED. So I'm a bit confused. But this is why I'm doing all this - to learn and figure things out myself.

Anyway, I ended up using a different piezo transducer when I moved to veroboard. This is what I ended up with:

2016-02-25 17.59.34-1

The strange thing (for me) is that the LED/buzzer remain lit/buzzing if the power is on but no signal is being received by the Rx. So I've obviously screwed up somewhere in my simple design. But, it works enough for my purposes!

The next step will be to figure out how to mount this on my handlebars. I need to also implement the MaxBotix sensor on a new prototyping board, with an antenna for the transmitter. Then I'll be able to give my Bike Sonar, Mk. 2 a test run.