Like most of us, I'm still impatiently waiting for my Raspberry Pi. I've ordered mine after the launch sold-out date and I suspect it will come even later. I'm really waiting for two things: my RasPi, and my self-designed expansion PCB blanks, which I call Raspy Juice.
The main features of the Raspy Juice expansion board are:
- 6-20V input to 5V 3A buck regulator
- RS232 level translator, with a 2.5mm stereo connector (self-requirement)
- RTC based on PCF8523
Whilst designing the above, the PCB initially "looked" sparse, so I added some secondary features: an ATmega168A expansion micro-controller connected to the I2C and supposed to control:
- 4-channel RC servo interface (PC0, PC1, PC2, PC3)
- RS485 interface (USART0, must be bit-accurate to 115200,8N1)
- RS232 interface (software-based UART, mainly at 9600,8N1)
(The above last two interfaces are meant for other simple robotics expansion boards, not "industrial-strength" stuff).
My projects wish-list for this RasPi and Raspy-Juice combination are for:
- Replace my aging Gumstix Overo-Tobi home server with RasPi and 2 attached USB HDD. With 3A, I think the Raspy-Juice will have enough power, but I may have to circumvent RasPi's USB port fuses.
- Build a battery-powered, smallish and almost headless demonstration gadget with RC servos attached.
- Help someone else build her moving paper mache "Eye of Sauron" project with a webcam. (The webcam part was my idea 8-).
My micro-controller programming skills aren't bad, but not great either. I know I can get blinking-LED, servo movement and eventually, serial interfaces working through userspace I2C read-writes. But I have my sights on something more like PyMCU (or really, just a small subset will do).
Is there anyone interested in such a expansino board? I can hope to assemble additional prototypes (when the blanks finally arrive and working to some extent, that is) if there is some interest… (If there's too much interest, however, I'll have to put it up on a webshop .
Downsides of my design:
- Probably I can't test the hardware completely, because I've no actual RasPi.
- Probably I can't write I2C code properly, because I've no actual RasPi. (Starting to rant).
- It's also too bad that the PCB is so small, that I had to sacrifice convenient MCU programmability through RasPi's SPI pins (routing constraints). The only way to program the MCU is one would've to own an AVR 6-pin programmer.
- And then there's the danger of bricking the AVR should some incorrect fuse programming is performed. There's no way to recover from this, apart from re-soldering the DFN chip (hard, hard, hard ;-().
- At worst, we're left with just a PSU regulator PCB (and that is, if it even works. No PCB's, unbuilt and untested as yet).