Project Objective:Develop an open source AIS Alarm that alerts sailors that a new marine vessel with AIS is within range
The breadboard prototyping and first pass at firmware are sufficient to proceed to hardware design. After exchanges with the developer of dAISy and some early layout I have modified the pins used by the microcontroller and foresee the need to refactor the firmware. At this point though no show stoppers are foreseen. This post will describe the preliminary schematic and what drove some of the decisions.
On the left is a programming header for the MSP430FR2111 and a pin header for connecting to the dAISy module. The MSP430FR2111 will be programmed with pogo pins and the connection with the dAISy module will be by ribbon cable. The support circuity for the microcontroller is the same as in previous posts with the addition of a 5V rail which will be used to drive the alarm buzzer and LED. Status is given by dual LED right angle indicator driven directly from the microcontroller. User input is from two right angle momentary switches. The alarm will have a right angle LED drawing around 25 mA. The PCB will have a footprint for both SMD and through hole parts as a final decision has not been made. Current will be on the order of 25 mA and I will probably alternate beeping the buzzer with blinking the alarm LED to minimize current draw.
I received excellent feedback from element14 member in this thread on how to maximize the sound from a buzzer. Among the suggestions I have incorporated in the design are 1) use of a N channel MOSFET instead of a NPN transistor, 2) maximizing current within the constraints of my supply, and 3) a search for the most efficient piezo buzzer I could find that fit the design.