USB-to-1-wire adapter with galvanic isolation


Using long wires through workshops or buildings connected to the precious computer’s ground line is not the greatest idea concerning EMI and noise impact as well as operators’ safety. A system with separated grounds, the 1-wire-bus isolated from the USB and the computer, would improve reliability and availability of that measuring system even under influence of electrical noise, lightning or ground voltage disturbances.

The isolated transfer of power uses a transformer and rectifier assembly, here build with a digital bus driver circuit 74HC245 and a 1:1:1 ferrite transformer (3 identical windings). This provides low power, high efficiency and utilisation of readily-available low-cost parts.
The transfer of RS232 information uses high speed optocouplers 6N136. A low-cost hex Schmitt inverter HCMOS IC 74HC14 is used on the isolated side for the processing of the filtered 1-Wire-signals and LED drive to reduce the overall component count.