I’m working on creating my first circuit board for a hobby personal device. This is my first pass at what will be an expanding board.
My goal is to build a board that has the following functionality in order of importance in the smallest package possible. This will eventually go in a weatherproof box. Smaller board = less PCB and box cost.
- Solid State Relay Controller
- Current sinking pulse output reading (not yet in schematic)
- Logic level AC current meter (yes or no current is flowing, not yet in schematic)
I’d like anyone’s input on what design flaws I might have up to this point. I’m in the process of really breaking down the voltage and current everywhere in the circuit, but I’m inexperienced and the internet if full of great people that can see flaws in an instant. The system works on the general principles: 12V input is converted to 5V, 5V Drives the Boron, 3.3V from the boron drives the GPS chip and the MOSFET controlling the 12V relay circuit. The power supply is pretty standard since I followed the recommended circuit out of the LM2675 DC voltage converter documentation.
VCC_2 = 12V
VCC = 5V
VCC3.3 = 3.3V
My main questions/concerns.
- Relay indicator LED. When the MOSFET is off, the LED will be on with 5mA flowing from the 12V to 5V through the relay. When the MOSFET is activated, the LED will go off and 15mA will flow through the relay (sufficient for activation). Is this an acceptable configuration? The Relay didn’t specify a minimum activation current unfortunately.
- GPS – I’m planning on installing the Adafruit Ultimate GPS on the GPS headers. In my test, it works just fine connecting the TX,RX,GND, 3.3V pins; however do I need any other circuitry for power or interference control? The asset tracker has tons of circuitry, so I’m not sure how much of that I need.
- Bridge rectifier needed? I saw a few circuits that had one but it mostly seems to be for production environments when users may install things correctly. Since this is personal and I know how to hook it up, is it still a good idea to keep it in?
- Does anyone have a good circuit for current sinking pulse output pulse reading? In my field test, my researched circuit didn’t work. What did work (super sketchy) was putting the ground to Boron Ground and the + straight into a Boron Pin and measured correctly with an interrupt. It may have worked, but that’s just luck. I’d like to use an optocoupler or something to keep it as an optically isolated system.