This folder contains definition of the electronic part of the Hat.
Schematic and PCBs habe made starting with template from mikelawrence.
Files can be edited with Kicad PCB , a Cross Platform and Open Source Electronics Design Automation Suite .
Some explanation :
- U2 BTS452T is a Smart Power Switch to power the PI through the Traco regulator TSR 2-2450. C3 is not mandatory but recommended by the Traco application note if input voltage of 24V is used.
- D1 and D5 are to power the 78L33 regulator and then the arduino ATTINY 45 from Vacc or from the U2 power switch.
- In case of usage with a 24V car battery, in charge voltage can grow up to 28 V (normal operation) or even 32 V (overvoltage situation). D2, D3, D4 are there to protect the 78L33 input (maximun rating 30V) in this case.
- R1 are R2 are a divider to provide Vacc voltage information to the ATTINY 45 through analog input AN3.
- R4, R5 are pull-up for communication I2C bus between the ATTINY 45 and the PI
- JP1 : pin 1 and 2 need to be shorten as the SHUTDOWN request is now done through the I2C bus and not through a dedicated digital input
- J3, J4, R3, D6 are not necessary for a generci usage and were dedicated to data saving of GPS chipset
- R11, R12, R13, R14, U6, U7 are there for additionnal isolated input. But I've never sold neither tested them. Forget them.
References of used components can be browsed by opening schematic file (RaspPowerHat.sch) with KiCad PCB.
File package to order PCB manufacturing can be found here
Here is the result with hand soldering. It is possible to use stackable header to add another PI hat on top of it. The Hat is larger than a standard PI Zero one to the 5 leds.
- Front side:
The switched regulator TSR 2-2450 normaly sold on the front side (as on the design) can also be sold on the back side to adjust height of the PCB stack.
- Back side :
You can now find the ATTINY 45 firmware here