I'm designing an Open Hardware door-lock-controller for our hackerspace, to these basic requirements:
- Be made exclusively from available and inexpensive parts.
- Read external Wiegand keyboard
- Read external Wiegand RFID reader
- Control various door-locks and other actuators.
- Read 125 kHz EM4100 RFID directly with an onboard reader.
- Passive POE powered, to make cabling easier.
- Run off unregulated 15-30V DC (cheap and easy high-capacity UPS via SLA)
- Provide a regulated 12V DC out @ 300 mA to 1.5A peak for external gear.
- Talk Ethernet to the server.
- Keep a local list of allowable keys, so only power is needed to let us in.
- Control external 230V gear using two relays.
This is the second spin of the PCB with a few changes to fix the problems I've found, the biggest change I've made is to throw away the LDO that regulated the 3.3V rail, in exchange for a simple MC34063 based switcher.
I'm pretty sure it's going to work, but I'd like some comments to check if I've overlooked something.
Compromises I've had to make in the design are:
- The primary (35V) capacitor is stacked on top of the Ethernet transformer to save space.
- The Ethernet transformer is huge, but I have a bunch of them and they were cheap, so I'm going to use them, even if they are huge.
- Is there a cheaper and better way to implement the two power supplies (I need around 200mA@3.3V and 300mA@12V with peaks to 1.5A) ?
- Does the MC34063 switcher circuit/layout look sane?
- I have no idea how inefficient the MC34063 is so I've tried to heat sink it as well as possible using the copper I have available, any hints for improvements?