Figure 1. If you look carefully you'll see the new addition at the bottom left hand corner and if you look very very carefully an attached DS2401!
(and 3 Oscilloscope leads - two for I2C bus observation and the other for 1-Wire bus observation).
As previously mentioned that the COMPACT TOP HAT would support the 1-wire interface.
Well that feature has come to fruition with the delivery of some DS2482S-100+ Single Channel 1-Wire Masters.
This little chip saves the Raspberry Pi from bit bashing or banging one of its GPIO ports.
Figure 2. The extension board
I quickly whipped up a extension PCB, assembled it and it works!
The board attaches to the COMPACT TOP HAT I2C port has a pass through port to enable connection to the other I2C peripherals.
Figure 3. 1-Wire bus signal captured on TEK TBS1052-EDU. (It is of 0x33 - READ ROM Command)
I tested it using a DS2401 addressable switch. This little TO-92 IC can act as either a security key or rudimentary door switch detector.
Only two of the pins are used - a GND and the 1-Wire interface pin. It's power is derived from the 1-Wire interface pin.
When connected in series with a door switch - if you can read the serial number then the door switch is closed otherwise you'd get no acknowledge signal meaning that door switch must be open (or something is busted!).
Figure 4. A(n angled) screen shot of the results of hot swapping DS2401s and showing the RPi reading their Serial Numbers.
At an additional cost I could have used DS2482S-800+ Eight Channel 1-Wire Masters to give me more 1-wire busses.
The DS2483 has only 6 pins and supports multiple voltages and sleep mode for power sensitive applications but is currently unavailable from e14.
It is not mandatory to use a DS2482S-100+ because an I2C based 1-Wire Master could also be effectively accomplished using a PSoC.