Monday, November 28, 2016

IR receiver + IR transmitter + RTC for Raspberry Pi

I needed an IR receiver for my Raspberry Pi which I use as an internet TV receiver with some custom program.  As expected, I could not find any IR receiver module that fits nicely in my favorite simple & discreet Rasperry Pi case which only exposes all connectors and GPIO.  A USB adapter was an option, but I did not want anything sticking out of the pi.  Solution: make my own.

The board is shaped so it fits nicely in the case.   Since there was plenty of board space left, I also put an IR transmitter and RTC (DS1308U)+battery in addition to the IR receiver.  The IR receiver and transmitter are connected to the standard LIRC GPIOs (GPIO18 for receiver and GPIO17 for transmitter).  The RTC is connected to the I2C bus, and is compatible with the DS1307 driver which is included in the current Raspibian Kernel.   All GPIOs used on this board belong to the upper 12 pins of the GPIO header so a 12-pin female connector can be used instead of a full 40 pin (SMT 40-pin female connectors are really pricey!)



The PCB is available here.

A low-power battery-operated 2-to-1 stereo combiner

I was shopping for a simple compact device which simply combines two stereo inputs into one, but couldn't find such a thing.  There are a bunch of products with fancy mixing and such, but I am not interested in those.  Long-life battery operation was another thing I was looking for.  My solution turned out to be making my own.

This is just a couple of text-book inverting amplifiers with AC coupling on both inputs and output sides to minimize DC current draw from the battery.  This way, DC current draw from the battery consists of just the opamps and the voltage divider for common mode generation.  Total DC current draw should not exceed 21 uA.  Optimistic battery life expectation is 220 mAh (from CR2032)  / 21 uA  = 416 days which of course depends on the actual usage of the device.

The PCB can be ordered at (I do not make any money).